Joseph, DB; Chandrashekar, AS; Abler, LL; Chu, LF; Thomson, JA; Mendelsohn, C; Vezina, CM. Proc Natl Acad Sci U S A. vol. 115(33), 8394–8399. August 2018.
The bladder’s remarkable regenerative capacity had been thought to derive exclusively from its own progenitors. While examining consequences of DNA methyltransferase 1 (Dnmt1) inactivation in mouse embryonic bladder epithelium, we made the surprising discovery that Wolffian duct epithelial cells can support bladder regeneration. Conditional Dnmt1 inactivation in mouse urethral and bladder epithelium triggers widespread apoptosis, depletes basal and intermediate bladder cells, and disrupts uroplakin protein expression. These events coincide with Wolffian duct epithelial cell recruitment into Dnmt1 mutant urethra and bladder where they are reprogrammed to express bladder markers, including FOXA1, keratin 5, P63, and uroplakin. This is evidence that Wolffian duct epithelial cells are summoned in vivo to replace damaged bladder epithelium and function as a reservoir of cells for bladder regeneration.
Wegner, KA; Abler, LL; Oakes, SR; Mehta, GS; Ritter, KE; Hill, WG; Zwaans, BMM; Lamb, LE; Wang, Z; Bjorling, DE; Ricke, WA; Macoska, J; Marker, PC; Southard-Smith, EM; Eliceiri, KW; Vezina, CM.. Am J Physiol Renal Physiol. July 2018.
Mouse urinary behavior is quantifiable and used to pinpoint mechanisms of voiding dysfunction and evaluate potential human therapies. Approaches to evaluate mouse urinary function vary widely among laboratories, however, complicating cross-study comparisons. Here, we describe development and multi-institutional validation of a new tool for objective, consistent and rapid analysis of mouse void spot assay (VSA) data. Void Whizzard is a freely available software plugin for FIJI (a distribution of ImageJ) that facilitates VSA image batch processing and data extraction. We describe its features, demonstrate them by evaluating how specific VSA method parameters influence voiding behavior, and establish Void Whizzard as an expedited method for VSA analysis. This study includes control and obese diabetic mice as models of urinary dysfunction to increase rigor and ensure relevance across distinct voiding patterns. In particular, we show that Void Whizzard is an effective tool for quantifying non-concentric overlapping void spots, which commonly confound analyses. We also show that mouse genetics are consistently more influential than assay design parameters when it comes to VSA outcomes. None of the following procedural modifications to reduce overlapping spots masked these genetic-related differences: reduction of VSA testing duration, water access during the assay period, placement of a wire mesh cage bottom on top of or elevated over the filter paper, treatment of mesh with a hydrophobic spray, and size of wire mesh opening. The Void Whizzard software and rigorous validation of VSA methodological parameters described here advance the goal of standardizing mouse urinary phenotyping for comprehensive urinary phenome analyses.
Lindström, NO; McMahon, JA; Guo, J; Tran, T; Guo, Q; Rutledge, E; Parvez, RK; Saribekyan, G; Schuler, RE; Liao, C; Kim, AD; Abdelhalim, A; Ruffins, SW; Thornton, ME; Basking, L; Grubbs, B; Kesselman, C; McMahon, AP. J Am Soc Nephrol. February 2018.
Human kidney function is underpinned by approximately 1,000,000 nephrons, although the number varies substantially, and low nephron number is linked to disease. Human kidney development initiates around 4 weeks of gestation and ends around 34-37 weeks of gestation. Over this period, a reiterative inductive process establishes the nephron complement. Studies have provided insightful anatomic descriptions of human kidney development, but the limited histologic views are not readily accessible to a broad audience. In this first paper in a series providing comprehensive insight into human kidney formation, we examined human kidney development in 135 anonymously donated human kidney specimens. We documented kidney development at a macroscopic and cellular level through histologic analysis, RNA in situ hybridization, immunofluorescence studies, and transcriptional profiling, contrasting human development (4-23 weeks) with mouse development at selected stages (embryonic day 15.5 and postnatal day 2). The high-resolution histologic interactive atlas of human kidney organogenesis generated can be viewed at the GUDMAP database (www.gudmap.org) together with three-dimensional reconstructions of key components of the data herein. At the anatomic level, human and mouse kidney development differ in timing, scale, and global features such as lobe formation and progenitor niche organization. The data also highlight differences in molecular and cellular features, including the expression and cellular distribution of anchor gene markers used to identify key cell types in mouse kidney studies. These data will facilitate and inform in vitro efforts to generate human kidney structures and comparative functional analyses across mammalian species.
Lindström, NO; Guo, J; Kim, AD; Tran, T; Guo, Q; De Sena Brandine, G; Ransick, A; Parvez, RK; Thornton, ME; Basking, L; Grubbs, B; McMahon, JA; Smith, AD; McMahon, AP. J Am Soc Nephrol. February 2018.
Cellular interactions among nephron, interstitial, and collecting duct progenitors drive mammalian kidney development. In mice, Six2+ nephron progenitor cells (NPCs) and Foxd1+ interstitial progenitor cells (IPCs) form largely distinct lineage compartments at the onset of metanephric kidney development. Here, we used the method for analyzing RNA following intracellular sorting (MARIS) approach, single-cell transcriptional profiling, in situ hybridization, and immunolabeling to characterize the presumptive NPC and IPC compartments of the developing human kidney. As in mice, each progenitor population adopts a stereotypical arrangement in the human nephron-forming niche: NPCs capped outgrowing ureteric branch tips, whereas IPCs were sandwiched between the NPCs and the renal capsule. Unlike mouse NPCs, human NPCs displayed a transcriptional profile that overlapped substantially with the IPC transcriptional profile, and key IPC determinants, including FOXD1, were readily detected within SIX2+ NPCs. Comparative gene expression profiling in human and mouse Six2/SIX2+ NPCs showed broad agreement between the species but also identified species-biased expression of some genes. Notably, some human NPC-enriched genes, including DAPL1 and COL9A2, are linked to human renal disease. We further explored the cellular diversity of mesenchymal cell types in the human nephrogenic niche through single-cell transcriptional profiling. Data analysis stratified NPCs into two main subpopulations and identified a third group of differentiating cells. These findings were confirmed by section in situ hybridization with novel human NPC markers predicted through the single-cell studies. This study provides a benchmark for the mesenchymal progenitors in the human nephrogenic niche and highlights species-variability in kidney developmental programs.
Lindström, NO; Tran, T; Guo, J; Rutledge, E; Parvez, RK; Thornton, ME; Grubbs, B; McMahon, JA; McMahon, AP. J Am Soc Nephrol. February 2018.
The nephron is the functional unit of the kidney, but the mechanism of nephron formation during human development is unclear. We conducted a detailed analysis of nephron development in humans and mice by immunolabeling, and we compared human and mouse nephron patterning to describe conserved and divergent features. We created protein localization maps that highlight the emerging patterns along the proximal–distal axis of the developing nephron and benchmark expectations for localization of functionally important transcription factors, which revealed unanticipated cellular diversity. Moreover, we identified a novel nephron subdomain marked by Wnt4 expression that we fate-mapped to the proximal mature nephron. Significant conservation was observed between human and mouse patterning. We also determined the time at which markers for mature nephron cell types first emerge—critical data for the renal organoid field. These findings have conceptual implications for the evolutionary processes driving the diversity of mammalian organ systems. Furthermore, these findings provide practical insights beyond those gained with mouse and rat models that will guide in vitro efforts to harness the developmental programs necessary to build human kidney structures.
Ryan, D; Sutherland, MR; Flores, TJ; Kent, AL; Dahlstrom, JE; Puelles, VG; Bertram, JF; McMahon, AP; Little, MH; Moore, L; Black, MJ. EBioMedicine. vol. 27, 275–283. January 2018.
BACKGROUND: During normal human kidney development, nephrogenesis (the formation of nephrons) is complete by term birth, with the majority of nephrons formed late in gestation. The aim of this study was to morphologically examine nephrogenesis in fetal human kidneys from 20 to 41weeks of gestation. METHODS: Kidney samples were obtained at autopsy from 71 infants that died acutely in utero or within 24h after birth. Using image analysis, nephrogenic zone width, the number of glomerular generations, renal corpuscle cross-sectional area and the cellular composition of glomeruli were examined. Kidneys from female and male infants were analysed separately. FINDINGS: The number of glomerular generations formed within the fetal kidneys was directly proportional to gestational age, body weight and kidney weight, with variability between individuals in the ultimate number of generations (8 to 12) and in the timing of the cessation of nephrogenesis (still ongoing at 37weeks gestation in one infant). There was a slight but significant (r2=0.30, P=0.001) increase in renal corpuscle cross-sectional area from mid gestation to term in females, but this was not evident in males. The proportions of podocytes, endothelial and non-epithelial cells within mature glomeruli were stable throughout gestation. INTERPRETATION: These findings highlight spatial and temporal variability in nephrogenesis in the developing human kidney, whereas the relative cellular composition of glomeruli does not appear to be influenced by gestational age.
Wegner, KA; Cadena, MT; Trevena, R; Turco, AE; Gottschalk, A; Halberg, RB; Guo, J; McMahon, JA; McMahon, AP; Vezina, CM. PLoS ONE. vol. 12(11) November 2017.
Adam, M; Potter, AS; Potter, SS. Development. vol. 144(19), 3625–3632. October 2017.
Single-cell RNA-seq is a powerful technique. Nevertheless, there are important limitations, including the technical challenges of breaking down an organ or tissue into a single-cell suspension. Invariably, this has required enzymatic incubation at 37°C, which can be expected to result in artifactual changes in gene expression patterns. Here, we describe a dissociation method that uses a protease with high activity in the cold, purified from a psychrophilic microorganism. The entire procedure is carried out at 6°C or colder, at which temperature mammalian transcriptional machinery is largely inactive, thereby effectively ‘freezing in’ the in vivo gene expression patterns. To test this method, we carried out RNA-seq on 20,424 single cells from postnatal day 1 mouse kidneys, comparing the results of the psychrophilic protease method with procedures using 37°C incubation. We show that the cold protease method provides a great reduction in gene expression artifacts. In addition, the results produce a single-cell resolution gene expression atlas of the newborn mouse kidney, an interesting time in development when mature nephrons are present yet nephrogenesis remains extremely active.
Wiese, CB; Deal, KK; Ireland, SJ; Cantrell, VA; Southard-Smith, EM. Dev Biol. vol. 429(1), 356–369. September 2017.
Ritter, KE; Southard-Smith, EM. Front Neurosci. vol. 10(592) June 2017.
Phan, TX; Ton, HT; Chen, Y; Basha, ME; Ahern, GP. Am J Physiol Renal Physiol. vol. 311(5), F1063–F1073. November 2016.
Armfield, BA; Seifert, AW; Zheng, Z; Merton, EM; Rock, JR; Lopez, MC; Baker, HV; Cohn, MJ. J Urol. vol. 196(4), 1295–302. October 2016.
Carpenter, AR; Becknell, MB; Ching, CB; Cuaresma, EJ; Chen, X; Hains, DS; McHugh, K. Kidney Int. vol. 89(3), 612–24. March 2016.
O’Brien, LL; Guo, Q; Lee, Y; Tran, T; Benazet, JD; Whitney, PH; Valouev, A; McMahon, AP. Development. vol. 143(4), 595–608. February 2016.
Nephron endowment is determined by the self-renewal and induction of a nephron progenitor pool established at the onset of kidney development. In the mouse, the related transcriptional regulators Six1 and Six2 play non-overlapping roles in nephron progenitors. Transient Six1 activity prefigures, and is essential for, active nephrogenesis. By contrast, Six2 maintains later progenitor self-renewal from the onset of nephrogenesis. We compared the regulatory actions of Six2 in mouse and human nephron progenitors by chromatin immunoprecipitation followed by DNA sequencing (ChIP-seq). Surprisingly, SIX1 was identified as a SIX2 target unique to the human nephron progenitors. Furthermore, RNA-seq and immunostaining revealed overlapping SIX1 and SIX2 activity in 16 week human fetal nephron progenitors. Comparative bioinformatic analysis of human SIX1 and SIX2 ChIP-seq showed each factor targeted a similar set of cis-regulatory modules binding an identical target recognition motif. In contrast to the mouse where Six2 binds its own enhancers but does not interact with DNA around Six1, both human SIX1 and SIX2 bind homologous SIX2 enhancers and putative enhancers positioned around SIX1. Transgenic analysis of a putative human SIX1 enhancer in the mouse revealed a transient, mouse-like, pre-nephrogenic, Six1 regulatory pattern. Together, these data demonstrate a divergence in SIX-factor regulation between mouse and human nephron progenitors. In the human, an auto/cross-regulatory loop drives continued SIX1 and SIX2 expression during active nephrogenesis. By contrast, the mouse establishes only an auto-regulatory Six2 loop. These data suggest differential SIX-factor regulation might have contributed to species differences in nephron progenitor programs such as the duration of nephrogenesis and the final nephron count.
McMahon, AP. Curr Top Dev Biol. vol. 117, 31–64. January 2016.
The basic unit of kidney function is the nephron. In the mouse, around 14,000 nephrons form in a 10-day period extending into early neonatal life, while the human fetus forms the adult complement of nephrons in a 32-week period completed prior to birth. This review discusses our current understanding of mammalian nephrogenesis: the contributing cell types and the regulatory processes at play. A conceptual developmental framework has emerged for the mouse kidney. This framework is now guiding studies of human kidney development enabled in part by in vitro systems of pluripotent stem cell-seeded nephrogenesis. A near future goal will be to translate our developmental knowledge-base to the productive engineering of new kidney structures for regenerative medicine.
Keast, JR; Smith-Anttila, CJ; Osborne, PB. Front Cell Dev Biol. vol. 3, 53. September 2015.
The development of organs occurs in parallel with the formation of their nerve supply. The innervation of pelvic organs (lower urinary tract, hindgut, and sexual organs) is complex and we know remarkably little about the mechanisms that form these neural pathways. The goal of this short review is to use the urinary bladder as an example to stimulate interest in this question. The bladder requires a healthy mature nervous system to store urine and release it at behaviorally appropriate times. Understanding the mechanisms underlying the construction of these neural circuits is not only relevant to defining the basis of developmental problems but may also suggest strategies to restore connectivity and function following injury or disease in adults. The bladder nerve supply comprises multiple classes of sensory, and parasympathetic or sympathetic autonomic effector (motor) neurons. First, we define the developmental endpoint by describing this circuitry in adult rodents. Next we discuss the innervation of the developing bladder, identifying challenges posed by this area of research. Last we provide examples of genetically modified mice with bladder dysfunction and suggest potential neural contributors to this state.
Ton, HT; Smart, AE; Aguilar, BL; Olson, TT; Kellar, KJ; Ahern, GP. Mol Pharmacol. vol. 88(2), 256–64. August 2015.
The α3β4 nicotinic acetylcholine receptor (nAChR) subtype is widely expressed in the peripheral and central nervous systems, including in airway sensory nerves. The nAChR subtype transduces the irritant effects of nicotine in tobacco smoke and, in certain brain areas, may be involved in nicotine addiction and/or withdrawal. Menthol, a widely used additive in cigarettes, is a potential analgesic and/or counterirritant at sensory nerves and may also influence nicotine’s actions in the brain. We examined menthol’s effects on recombinant human α3β4 nAChRs and native nAChRs in mouse sensory neurons. Menthol markedly decreased nAChR activity as assessed by Ca(2+) imaging, (86)Rb(+) efflux, and voltage-clamp measurements. Coapplication of menthol with acetylcholine or nicotine increased desensitization, demonstrated by an increase in the rate and magnitude of the current decay and a reduction of the current integral. These effects increased with agonist concentration. Pretreatment with menthol followed by its washout did not affect agonist-induced desensitization, suggesting that menthol must be present during the application of agonist to augment desensitization. Notably, menthol acted in a voltage-independent manner and reduced the mean open time of single channels without affecting their conductance, arguing against a simple channel-blocking effect. Further, menthol slowed or prevented the recovery of nAChRs from desensitization, indicating that it probably stabilizes a desensitized state. Moreover, menthol at concentrations up to 1 mM did not compete for the orthosteric nAChR binding site labeled by [(3)H]epibatidine. Taken together, these data indicate that menthol promotes desensitization of α3β4 nAChRs by an allosteric action.
Georgas, KM; Armstrong, J; Keast, JR; Larkins, CE; McHugh, KM; Southard-Smith, EM; Cohn, MJ; Batourina, E; Dan, H; Schneider, K; Buehler, DP; Wiese, CB; Brennan, J; Davies, JA; Harding, SD; Baldock, RA; Little, MH; Vezina, CM; Mendelsohn, C. Development. vol. 142(10), 1893–908. May 2015.
Malformation of the urogenital tract represents a considerable paediatric burden, with many defects affecting the lower urinary tract (LUT), genital tubercle and associated structures. Understanding the molecular basis of such defects frequently draws on murine models. However, human anatomical terms do not always superimpose on the mouse, and the lack of accurate and standardised nomenclature is hampering the utility of such animal models. We previously developed an anatomical ontology for the murine urogenital system. Here, we present a comprehensive update of this ontology pertaining to mouse LUT, genital tubercle and associated reproductive structures (E10.5 to adult). Ontology changes were based on recently published insights into the cellular and gross anatomy of these structures, and on new analyses of epithelial cell types present in the pelvic urethra and regions of the bladder. Ontology changes include new structures, tissue layers and cell types within the LUT, external genitalia and lower reproductive structures. Representative illustrations, detailed text descriptions and molecular markers that selectively label muscle, nerves/ganglia and epithelia of the lower urogenital system are also presented. The revised ontology will be an important tool for researchers studying urogenital development/malformation in mouse models and will improve our capacity to appropriately interpret these with respect to the human situation.
O’Brien, LL; McMahon, AP. Semin Cell Dev Biol. vol. 36, 31–8. December 2014.
The functional unit of the mammalian metanephric kidney is the nephron: a complex tubular structure dedicated to blood filtration and maintenance of several important physiological functions. Nephrons are assembled from a nephron-restricted pool of mesenchymal progenitors over an extensive developmental period that is completed prior to (human), or shortly after (mouse), birth. An appropriate balance in the expansion and commitment of nephron progenitors to nephron formation is essential for normal kidney function. Too few nephrons increase risk of kidney disease later in life while the failure of normal progenitor differentiation in Wilm’s tumor patients leads to massive growth of a nephroblast population often necessitating surgical removal of the kidney. An inductive process within the metanephric mesenchyme leads to the formation of a pretubular aggregate which transitions into an epithelial renal vesicle: the precursor for nephron assembly. Growth, morphogenesis and patterning transform this simple cyst-like structure into a highly elongated mature nephron with distinct cell types positioned along a proximal (glomerular) to distal (connecting segment) axis of functional organization. This review discusses our current understanding of the specification, maintenance and commitment of nephron progenitors, and the regulatory processes that transform the renal vesicle into a nephron.
Herrera, AM; Cohn, MJ. Sci Rep. vol. 4, 6896. November 2014.
Genital malformations occur at a high frequency in humans, affecting ~1:250 live births. The molecular mechanisms of external genital development are beginning to be identified; however, the origin of cells that give rise to external genitalia is unknown. Here we use cell lineage analysis to show that the genital tubercle, the precursor of the penis and clitoris, arises from two populations of progenitor cells that originate at the lateral edges of the embryo, at the level of the posterior hindlimb buds and anterior tail. During body wall closure, the left and right external genital progenitor pools are brought together at the ventral midline, where they form the paired genital swellings that give rise to the genital tubercle. Unexpectedly, the left and right external genital progenitor pools form two lineage-restricted compartments in the phallus. Together with previous lineage studies of limb buds, our results indicate that, at the pelvic level, the early lateral mesoderm is regionalized from medial to lateral into dorsal limb, ventral limb, and external genital progenitor fields. These findings have implications for the evolutionary diversification of external genitalia and for the association between external genital defects and disruption of body wall closure, as seen in the epispadias-extrophy complex.
Kumar, S; Liu, J; McMahon, AP. Semin Nephrol. vol. 34(4), 404–17. July 2014.
The mammalian kidney has an intrinsic ability to repair after significant injury. However, this process is inefficient: patients are at high risk for the loss of kidney function in later life. No therapy exists to treat established acute kidney injury (AKI) per se: strategies to promote endogenous repair processes and retard associated fibrosis are a high priority. Whole-organ gene expression profiling has been used to identify repair responses initiated with AKI, and factors that may promote the transition from AKI to chronic kidney disease. Transcriptional profiling has shown molecular markers and potential regulatory pathways of renal repair. Activation of a few key developmental pathways has been reported during repair. Whether these are comparable networks with similar target genes with those in earlier nephrogenesis remains unclear. Altered microRNA profiles, persistent tubular injury responses, and distinct late inflammatory responses highlight continuing kidney pathology. Additional insights into injury and repair processes will be gained by study of the repair transcriptome and cell-specific translatome using high-resolution technologies such as RNA sequencing and translational profiling tailored to specific cellular compartments within the kidney. An enhanced understanding holds promise for both the identification of novel therapeutic targets and biomarker-based evaluation of the damage-repair process.
Yamany, T; Van Batavia, J; Mendelsohn, C. Curr Opin Organ Transplant. vol. 19(3), 323–30. June 2014.
PURPOSE OF REVIEW: This review addresses significant changes in our understanding of urothelial development and regeneration. Understanding urothelial differentiation will be important in the push to find new methods of bladder reconstruction and augmentation, as well as identification of bladder cancer stem cells. RECENT FINDINGS: This review will cover recent findings including the identification of novel progenitor cells in the embryo and adult urothelium, function of the urothelium, and regeneration of the urothelium. Using Cre-lox recombination with cell-type-specific Cre lines, lineage studies from our laboratory have revealed novel urothelial cell types and progenitors that are critical for formation and regeneration of the urothelium. Interestingly, our studies indicate that Keratin-5-expressing basal cells, which have previously been proposed to be urothelial stem cells, are a self-renewing unipotent population, whereas P-cells, a novel urothelial cell type, are progenitors in the embryo, and intermediate cells serve as a progenitor pool in the adult. SUMMARY: These findings could have important implications for our understanding of cancer tumorigenesis and could move the fields of regeneration and reconstruction forward.
Little, MH; Brown, D.; Humphreys, BD; McMahon, AP; Miner, JH; Sands, JM; Weisz, OA; Mullins, C; Hoshizaki, D; Kidney Research National Dialogue, (KRND). Clin J Am Soc Nephrol. vol. 9(4), 809–11. April 2014.
The Kidney Research National Dialogue represents a novel effort by the National Institute of Diabetes and Digestive and Kidney Diseases to solicit and prioritize research objectives from the renal research and clinical communities. The present commentary highlights selected scientific opportunities specific to the study of renal development, physiology, and cell biology. Describing such fundamental kidney biology serves as a necessary foundation for translational and clinical studies that will advance disease care and prevention. It is intended that these objectives foster and focus scientific efforts in these areas in the coming decade and beyond.
Keil, KP; Altmann, HM; Mehta, V; Abler, LL; Elton, EA; Vezina, CM. Gene Expr Patterns. vol. 13(8), 413–24. December 2013.
The mouse prostate develops from a component of the lower urinary tract (LUT) known as the urogenital sinus (UGS). This process requires androgens and signaling between mesenchyme and epithelium. Little is known about DNA methylation during prostate development, including which factors are expressed, whether their expression changes over time, and if DNA methylation contributes to androgen signaling or influences signaling between mesenchyme and epithelium. We used in situ hybridization to evaluate the spatial and temporal expression pattern of mRNAs which encode proteins responsible for establishing, maintaining or remodeling DNA methylation. These include DNA methyltransferases, DNA deaminases, DNA glycosylases, base excision repair and mismatch repair pathway members. The mRNA expression patterns were compared between male and female LUT prior to prostatic bud formation (14.5 days post coitus (dpc)), during prostatic bud formation (17.5 dpc) and during prostatic branching morphogenesis (postnatal day (P) 5). We found dramatic changes in the patterns of these mRNAs over the course of prostate development and identified examples of sexually dimorphic mRNA expression. Future investigation into how DNA methylation patterns are established, maintained and remodeled during the course of embryonic prostatic bud formation may provide insight into prostate morphogenesis and disease.
Gandhi, D; Molotkov, A; Batourina, E; Schneider, K; Dan, H; Reiley, M; Laufer, E; Metzger, D; Liang, F; Liao, Y; Sun, TT; Aronow, B; Rosen, R; Mauney, J; Adam, R; Rosselot, C; Van Batavia, J; McMahon, AP; McMahon, J; Guo, JJ; Mendelsohn, C. Dev Cell. vol. 26(5), 469–482. September 2013.
The urothelium is a multilayered epithelium that serves as a barrier between the urinary tract and blood, preventing the exchange of water and toxic substances. It consists of superficial cells specialized for synthesis and transport of uroplakins that assemble into a tough apical plaque, one or more layers of intermediate cells, and keratin 5-expressing basal cells (K5-BCs), which are considered to be progenitors in the urothelium and other specialized epithelia. Fate mapping, however, reveals that intermediate cells rather than K5-BCs are progenitors in the adult regenerating urothelium, that P cells, a transient population, are progenitors in the embryo, and that retinoids are critical in P cells and intermediate cells, respectively, for their specification during development and regeneration. These observations have important implications for tissue engineering and repair and, ultimately, may lead to treatments that prevent loss of the urothelial barrier, a major cause of voiding dysfunction and bladder pain syndrome.
Keil, KP; Mehta, V; Branam, AM; Abler, LL; Bresh-Stiemke, RA; Joshi, PS; Schmitz, CT; Marker, PC; Vezina, CM. Endocrinology. vol. 153(12), 6091–103. December 2012.
Fetal prostate development from urogenital sinus (UGS) epithelium requires androgen receptor (AR) activation in UGS mesenchyme (UGM). Despite growing awareness of sexually dimorphic gene expression in the UGS, we are still limited in our knowledge of androgen-responsive genes in UGM that initiate prostate ductal development. We found that WNT inhibitory factor 1 (Wif1) mRNA is more abundant in male vs. female mouse UGM in which its expression temporally and spatially overlaps androgen-responsive steroid 5α-reductase 2 (Srd5a2). Wif1 mRNA is also present in prostatic buds during their elongation and branching morphogenesis. Androgens are necessary and sufficient for Wif1 expression in mouse UGS explant mesenchyme, and testicular androgens remain necessary for normal Wif1 expression in adult mouse prostate stroma. WIF1 contributes functionally to prostatic bud formation. In the presence of androgens, exogenous WIF1 protein increases prostatic bud number and UGS basal epithelial cell proliferation without noticeably altering the pattern of WNT/β-catenin-responsive Axin2 or lymphoid enhancer binding factor 1 (Lef1) mRNA. Wif1 mutant male UGSs exhibit increased (Sfrp)2 and (Sfrp)3 expression and form the same number of prostatic buds as the wild-type control males. Collectively our results reveal Wif1 as one of the few known androgen-responsive genes in the fetal mouse UGM and support the hypothesis that androgen-dependent Wif1 expression is linked to the mechanism of androgen-induced prostatic bud formation.
Keil, KP; Mehta, V; Abler, LL; Joshi, PS; Schmitz, CT; Vezina, CM. Differentiation. vol. 84(3), 232–9. October 2012.
The purpose of this study was to validate a combined in situ hybridization (ISH)/immunohistochemistry (IHC) staining method for visualizing and quantifying mouse prostatic buds. To refine animal usage in prostate development studies, we also determined whether a comparable number of prostatic buds were formed in male and female mouse urogenital sinus (UGS) explants grown in vitro in the presence of androgen. We used IHC to label UGS epithelium and ISH to label prostatic buds with one of three different prostatic bud marking riboprobes: a previously identified prostatic bud marker, NK-3 transcription factor, locus 1 (Nkx3-1), and two newly identified prostatic bud markers, wingless-related MMTV integration site 10b (Wnt10b) and ectodysplasin-A receptor (Edar). We calculated total buds formed per UGS and the proportion marked by each mRNA after male UGS development in vivo and male and female UGS development in vitro. Nkx3-1 was first to mark the prostate field during UGS development in vivo but all three mRNAs marked prostatic buds during later developmental stages. The mRNAs localized to different domains: Nkx3-1 was present along about half the prostatic bud length while Edar and Wnt10b were restricted to distal bud tips. None of the mRNAs marked all buds formed in vitro and the proportion marked was developmental stage- and gender-dependent. Nkx3-1 marked the highest proportion of prostatic buds during in vitro UGS development. Together, our results reveal that ISH staining of mouse UGS can be used to quantify prostatic bud number, Nkx3-1 is currently the best suited riboprobe for this method, and female UGSs cannot be used interchangeably with male UGSs when conducting prostate development studies in vitro. We also found that Nkx3-1, Edar, and Wnt10b mark different prostatic bud regions and are likely to be useful in future studies of regional differences in prostatic bud gene expression.
Wiese, CB; Ireland, S; Fleming, NL; Yu, J; Valerius, MT; Georgas, K; Chiu, HS; Brennan, J; Armstrong, J; Little, MH; McMahon, AP; Southard-Smith, EM. Front Neurosci. vol. 6, 130. September 2012.
Relative positions of neurons within mature murine pelvic ganglia based on expression of neurotransmitters have been described. However the spatial organization of developing innervation in the murine urogenital tract (UGT) and the gene networks that regulate specification and maturation of neurons within the pelvic ganglia of the lower urinary tract (LUT) are unknown. We used whole-mount immunohistochemistry and histochemical stains to localize neural elements in 15.5 days post coitus (dpc) fetal mice. To identify potential regulatory factors expressed in pelvic ganglia, we surveyed expression patterns for known or probable transcription factors (TF) annotated in the mouse genome by screening a whole-mount in situ hybridization library of fetal UGTs. Of the 155 genes detected in pelvic ganglia, 88 encode TFs based on the presence of predicted DNA-binding domains. Neural crest (NC)-derived progenitors within the LUT were labeled by Sox10, a well-known regulator of NC development. Genes identified were categorized based on patterns of restricted expression in pelvic ganglia, pelvic ganglia and urethral epithelium, or pelvic ganglia and urethral mesenchyme. Gene expression patterns and the distribution of Sox10+, Phox2b+, Hu+, and PGP9.5+ cells within developing ganglia suggest previously unrecognized regional segregation of Sox10+ progenitors and differentiating neurons in early development of pelvic ganglia. Reverse transcription-PCR of pelvic ganglia RNA from fetal and post-natal stages demonstrated that multiple TFs maintain post-natal expression, although Pax3 is extinguished before weaning. Our analysis identifies multiple potential regulatory genes including TFs that may participate in segregation of discrete lineages within pelvic ganglia. The genes identified here are attractive candidate disease genes that may now be further investigated for their roles in malformation syndromes or in LUT dysfunction.
Buehler, DP; Wiese, CB; Skelton, SB; Southard-Smith, EM. J Vis Exp. vol. 66 August 2012.
During development neural crest (NC)-derived neuronal progenitors migrate away from the neural tube to form autonomic ganglia in visceral organs like the intestine and lower urinary tract. Both during development and in mature tissues these cells are often widely dispersed throughout tissues so that isolation of discrete populations using methods like laser capture micro-dissection is difficult. They can however be directly visualized by expression of fluorescent reporters driven from regulatory regions of neuron-specific genes like Tyrosine hydroxylase (TH). We describe a method optimized for high yields of viable TH+ neuronal progenitors from fetal mouse visceral tissues, including intestine and lower urogenital tract (LUT), based on dissociation and fluorescence-activated cell sorting (FACS). The Th gene encodes the rate-limiting enzyme for production of catecholamines. Enteric neuronal progenitors begin to express TH during their migration in the fetal intestine and TH is also present in a subset of adult pelvic ganglia neurons . The first appearance of this lineage and the distribution of these neurons in other aspects of the LUT, and their isolation has not been described. Neuronal progenitors expressing TH can be readily visualized by expression of EGFP in mice carrying the transgene construct Tg(Th-EGFP)DJ76Gsat/Mmnc. We imaged expression of this transgene in fetal mice to document the distribution of TH+ cells in the developing LUT at 15.5 days post coitus (dpc), designating the morning of plug detection as 0.5 dpc, and observed that a subset of neuronal progenitors in the coalescing pelvic ganglia express EGFP. To isolate LUT TH+ neuronal progenitors, we optimized methods that were initially used to purify neural crest stem cells from fetal mouse intestine. Prior efforts to isolate NC-derived populations relied upon digestion with a cocktail of collagenase and trypsin to obtain cell suspensions for flow cytometry. In our hands these methods produced cell suspensions from the LUT with relatively low viability. Given the already low incidence of neuronal progenitors in fetal LUT tissues, we set out to optimize dissociation methods such that cell survival in the final dissociates would be increased. We determined that gentle dissociation in Accumax (Innovative Cell Technologies, Inc), manual filtering, and flow sorting at low pressures allowed us to achieve consistently greater survival (\textgreater70% of total cells) with subsequent yields of neuronal progenitors sufficient for downstream analysis. The method we describe can be broadly applied to isolate a variety of neuronal populations from either fetal or adult murine tissues.
Yu, J; Valerius, MT; Duah, M; Staser, K; Hansard, JK; Guo, JJ; McMahon, J; Vaughan, J; Faria, D; Georgas, K; Rumballe, B; Ren, Q; Krautzberger, AM; Junker, JP; Thiagarajan, RD; Machanick, P; Gray, PA; van Oudenaarden, A; Rowitch, DH; Stiles, CD; Ma, Q; Grimmond, SM; Bailey, TL; Little, MH; McMahon, AP. Development. vol. 139(10), 1863–73. May 2012.
Lengthy developmental programs generate cell diversity within an organotypic framework, enabling the later physiological actions of each organ system. Cell identity, cell diversity and cell function are determined by cell type-specific transcriptional programs; consequently, transcriptional regulatory factors are useful markers of emerging cellular complexity, and their expression patterns provide insights into the regulatory mechanisms at play. We performed a comprehensive genome-scale in situ expression screen of 921 transcriptional regulators in the developing mammalian urogenital system. Focusing on the kidney, analysis of regional-specific expression patterns identified novel markers and cell types associated with development and patterning of the urinary system. Furthermore, promoter analysis of synexpressed genes predicts transcriptional control mechanisms that regulate cell differentiation. The annotated informational resource (www.gudmap.org) will facilitate functional analysis of the mammalian kidney and provides useful information for the generation of novel genetic tools to manipulate emerging cell populations.
Thiagarajan, RD; Georgas, KM; Rumballe, BA; Lesieur, E; Chiu, HS; Taylor, D; Tang, DT; Grimmond, SM; Little, MH. PLoS ONE. vol. 6(2) February 2012.
The development of the mammalian kidney is well conserved from mouse to man. Despite considerable temporal and spatial data on gene expression in mammalian kidney development, primarily in rodent species, there is a paucity of genes whose expression is absolutely specific to a given anatomical compartment and/or developmental stage, defined here as ’anchor’ genes. We previously generated an atlas of gene expression in the developing mouse kidney using microarray analysis of anatomical compartments collected via laser capture microdissection. Here, this data is further analysed to identify anchor genes via stringent bioinformatic filtering followed by high resolution section in situ hybridisation performed on 200 transcripts selected as specific to one of 11 anatomical compartments within the midgestation mouse kidney. A total of 37 anchor genes were identified across 6 compartments with the early proximal tubule being the compartment richest in anchor genes. Analysis of minimal and evolutionarily conserved promoter regions of this set of 25 anchor genes identified enrichment of transcription factor binding sites for Hnf4a and Hnf1b, RbpJ (Notch signalling), PPARγ:RxRA and COUP-TF family transcription factors. This was reinforced by GO analyses which also identified these anchor genes as targets in processes including epithelial proliferation and proximal tubular function. As well as defining anchor genes, this large scale validation of gene expression identified a further 92 compartment-enriched genes able to subcompartmentalise key processes during murine renal organogenesis spatially or ontologically. This included a cohort of 13 ureteric epithelial genes revealing previously unappreciated compartmentalisation of the collecting duct system and a series of early tubule genes suggesting that segmentation into proximal tubule, loop of Henle and distal tubule does not occur until the onset of glomerular vascularisation. Overall, this study serves to illuminate previously ill-defined stages of patterning and will enable further refinement of the lineage relationships within mammalian kidney development.
Temporal transcriptional profiling of somatic and germ cells reveals biased lineage priming of sexual fate in the fetal mouse gonad
Jameson, SA; Natarajan, A; Cool, J; DeFalco, T; Maatouk, DM; Mork, L; Munger, SC; Capel, B. PLoS Genet. vol. 8(3) 2012.
The divergence of distinct cell populations from multipotent progenitors is poorly understood, particularly in vivo. The gonad is an ideal place to study this process, because it originates as a bipotential primordium where multiple distinct lineages acquire sex-specific fates as the organ differentiates as a testis or an ovary. To gain a more detailed understanding of the process of gonadal differentiation at the level of the individual cell populations, we conducted microarrays on sorted cells from XX and XY mouse gonads at three time points spanning the period when the gonadal cells transition from sexually undifferentiated progenitors to their respective sex-specific fates. We analyzed supporting cells, interstitial/stromal cells, germ cells, and endothelial cells. This work identified genes specifically depleted and enriched in each lineage as it underwent sex-specific differentiation. We determined that the sexually undifferentiated germ cell and supporting cell progenitors showed lineage priming. We found that germ cell progenitors were primed with a bias toward the male fate. In contrast, supporting cells were primed with a female bias, indicative of the robust repression program involved in the commitment to XY supporting cell fate. This study provides a molecular explanation reconciling the female default and balanced models of sex determination and represents a rich resource for the field. More importantly, it yields new insights into the mechanisms by which different cell types in a single organ adopt their respective fates.
Chen, H; Palmer, JS; Thiagarajan, RD; Dinger, ME; Lesieur, E; Chiu, H; Schulz, A; Spiller, C; Grimmond, SM; Little, MH; Koopman, P; Wilhelm, D. PLoS ONE. vol. 7(7) 2012.
In contrast to the developing testis, molecular pathways driving fetal ovarian development have been difficult to characterise. To date no single master regulator of ovarian development has been identified that would be considered the female equivalent of Sry. Using a genomic approach we identified a number of novel protein-coding as well as non-coding genes that were detectable at higher levels in the ovary compared to testis during early mouse gonad development. We were able to cluster these ovarian genes into different temporal expression categories. Of note, Lrrc34 and AK015184 were detected in XX but not XY germ cells before the onset of sex-specific germ cell differentiation marked by entry into meiosis in an ovary and mitotic arrest in a testis. We also defined distinct spatial expression domains of somatic cell genes in the developing ovary. Our data expands the set of markers of early mouse ovary differentiation and identifies a classification of early ovarian genes, thus providing additional avenues with which to dissect this process.
Rumballe, BA; Chiu, HS; Georgas, KM; Little, MH. Methods Mol Biol. vol. 886, 223–39. 2012.
Studies into the molecular basis of morphogenesis frequently begin with investigations into gene expression across time and cell type in that organ. One of the most anatomically informative approaches to such studies is the use of in situ hybridization, either of intact or histologically sectioned tissues. Here, we describe the optimization of this approach for use in the temporal and spatial analysis of gene expression in the urogenital system, from embryonic development to the postnatal period. The methods described are applicable for high throughput analysis of large gene sets. As such, ISH has become a powerful technique for gene expression profiling and is valuable for the validation of profiling analyses performed using other approaches such as microarrays.
Davies, JA; Little, MH; Aronow, B; Armstrong, J; Brennan, J; Lloyd-MacGilp, S; Armit, C; Harding, S; Piu, X; Roochun, Y; Haggarty, B; Houghton, D; Davidson, D; Baldock, R. Methods Mol Biol. vol. 886, 185–201. 2012.
The Genitourinary Development Molecular Atlas Project (GUDMAP) aims to document gene expression across time and space in the developing urogenital system of the mouse, and to provide access to a variety of relevant practical and educational resources. Data come from microarray gene expression profiling (from laser-dissected and FACS-sorted samples) and in situ hybridization at both low (whole-mount) and high (section) resolutions. Data are annotated to a published, high-resolution anatomical ontology and can be accessed using a variety of search interfaces. Here, we explain how to run typical queries on the database, by gene or anatomical location, how to view data, how to perform complex queries, and how to submit data.
Rumballe, BA; Georgas, KM; Combes, AN; Ju, AL; Gilbert, T; Little, MH. Dev Biol. vol. 360(1), 110–22. December 2011.
Nephron number in the mammalian kidney is known to vary dramatically, with postnatal renal function directly influenced by nephron complement. What determines final nephron number is poorly understood but nephron formation in the mouse kidney ceases within the first few days after birth, presumably due to the loss of all remaining nephron progenitors via epithelial differentiation. What initiates this event is not known. Indeed, whether nephron formation occurs in the same way at this time as during embryonic development has also not been examined. In this study, we investigate the key cellular compartments involved in nephron formation; the ureteric tip, cap mesenchyme and early nephrons; from postnatal day (P) 0 to 6 in the mouse. High resolution analyses of gene and protein expression indicate that loss of nephron progenitors precedes loss of ureteric tip identity, but show spatial shifts in the expression of cap mesenchyme genes during this time. In addition, cap mesenchymal volume and rate of proliferation decline prior to birth. Section-based 3D modeling and Optical Projection Tomography revealed a burst of ectopic nephron induction, with the formation of multiple (up to 5) nephrons per ureteric tip evident from P2. While the distal-proximal patterning of these nephrons occurred normally, their spatial relationship with the ureteric compartment was altered. We propose that this phase of nephron formation represents an acceleration of differentiation within the cap mesenchyme due to a displacement of signals within the nephrogenic niche.
Mehta, V; Abler, LL; Keil, KP; Schmitz, CT; Joshi, PS; Vezina, CM. Dev Dyn. vol. 240(11), 2548–60. November 2011.
Prostate development is influenced by β-catenin signaling, but it is unclear which β-catenin activators are involved, where they are synthesized, and whether their mRNA abundance is influenced by androgens. We identified WNT/β-catenin-responsive β-galactosidase activity in the lower urogenital tract (LUT) of transgenic reporter mice, but β-galactosidase activity differed among the four mouse strains we examined. We used in situ hybridization to compare patterns of Wnts, r-spondins (Rspos, co-activators of β-catenin signaling), β-catenin-responsive mRNAs, and an androgen receptor-responsive mRNA in wild type fetal male, fetal female, and neonatal male LUT. Most Wnt and Rspo mRNAs were present in LUT during prostate development. Sexually dimorphic expression patterns were observed for WNT/β-catenin-responsive genes, and for Wnt2b, Wnt4, Wnt7a, Wnt9b, Wnt10b, Wnt11, Wnt16, and Rspo3 mRNAs. These results reveal sexual differences in WNT/β-catenin signaling in fetal LUT, supporting the idea that this pathway may be directly or indirectly responsive to androgens during prostate ductal development.
Abler, LL; Keil, KP; Mehta, V; Joshi, PS; Schmitz, CT; Vezina, CM. Dev Dyn. vol. 240(10), 2364–77. October 2011.
Epithelial-stromal interactions in the lower urogenital tract (LUT) are integral to prostatic and seminal vesicle development in males, vaginal and uterine development in females, and urethral development in both sexes. Gene expression profiling of isolated LUT stroma and epithelium has unraveled mechanisms of LUT development, but such studies are confounded by heterogeneous and ill-defined cell sub-populations contained within each tissue compartment. We used in situ hybridization to synthesize a high-resolution molecular atlas of 17-day post-coitus fetal mouse LUT. We identified mRNAs that mark selective cell populations of the seminal vesicle, ejaculatory duct, prostate, urethra, and vagina, subdividing these tissues into 16 stromal and 8 epithelial sub-compartments. These results provide a powerful tool for mapping LUT gene expression patterns and also reveal previously uncharacterized sub-compartments that may play mechanistic roles in LUT development of which we were previously unaware.
Hendry, C; Rumballe, B; Moritz, K; Little, MH. Pediatr Nephrol. vol. 26(9), 1395–406. September 2011.
It has long been appreciated that the mammalian kidney arises via reciprocal interactions between an epithelial ureteric epithelium and the surrounding metanephric mesenchyme. More recently, lineage tracing has confirmed that the portion of the metanephric mesenchyme closest to the advancing ureteric tips, the cap mesenchyme, represents the progenitor population for the nephron epithelia. This Six2(+)Cited1(+) population undergoes self-renewal throughout nephrogenesis while retaining the potential to epithelialize. In contrast, the Foxd1(+) portion of the metanephric mesenchyme shows no epithelial potential, developing instead into the interstitial, perivascular, and possibly endothelial elements of the kidney. The cap mesenchyme rests within a nephrogenic niche, surrounded by the stroma and the ureteric tip. While the role of Wnt signaling in nephron induction is known, there remains a lack of clarity over the intrinsic and extrinsic regulation of cap mesenchyme specification, self-renewal, and nephron potential. It is also not known what regulates cessation of nephrogenesis, but there is no nephron generation in response to injury during the postnatal period. In this review, we will examine what is and is not known about this nephron progenitor population and discuss how an increased understanding of the regulation of this population may better explain the observed variation in final nephron number and potentially facilitate the reinitiation or prolongation of nephron formation.
Thiagarajan, RD; Cloonan, N; Gardiner, BB; Mercer, TR; Kolle, G; Nourbakhsh, E; Wani, S; Tang, D; Krishnan, K; Georgas, KM; Rumballe, BA; Chiu, HS; Steen, JA; Mattick, JS; Little, MH; Grimmond, SM. BMC Genomics. vol. 12, 441. September 2011.
BACKGROUND: The developing mouse kidney is currently the best-characterized model of organogenesis at a transcriptional level. Detailed spatial maps have been generated for gene expression profiling combined with systematic in situ screening. These studies, however, fall short of capturing the transcriptional complexity arising from each locus due to the limited scope of microarray-based technology, which is largely based on "gene-centric" models. RESULTS: To address this, the polyadenylated RNA and microRNA transcriptomes of the 15.5 dpc mouse kidney were profiled using strand-specific RNA-sequencing (RNA-Seq) to a depth sufficient to complement spatial maps from pre-existing microarray datasets. The transcriptional complexity of RNAs arising from mouse RefSeq loci was catalogued; including 3568 alternatively spliced transcripts and 532 uncharacterized alternate 3’ UTRs. Antisense expressions for 60% of RefSeq genes was also detected including uncharacterized non-coding transcripts overlapping kidney progenitor markers, Six2 and Sall1, and were validated by section in situ hybridization. Analysis of genes known to be involved in kidney development, particularly during mesenchymal-to-epithelial transition, showed an enrichment of non-coding antisense transcripts extended along protein-coding RNAs. CONCLUSION: The resulting resource further refines the transcriptomic cartography of kidney organogenesis by integrating deep RNA sequencing data with locus-based information from previously published expression atlases. The added resolution of RNA-Seq has provided the basis for a transition from classical gene-centric models of kidney development towards more accurate and detailed "transcript-centric" representations, which highlights the extent of transcriptional complexity of genes that direct complex development events.
Abler, LL; Mehta, V; Keil, KP; Joshi, PS; Flucus, CL; Hardin, HA; Schmitz, CT; Vezina, CM. J Vis Exp. vol. 54 August 2011.
Development of the lower urogenital tract (LUT) is an intricate process. This complexity is evidenced during formation of the prostate from the fetal male urethra, which relies on androgenic signals and epithelial-mesenchymal interactions(1,2). Understanding the molecular mechanisms responsible for prostate development may reveal growth mechanisms that are inappropriately reawakened later in life to give rise to prostate diseases such as benign prostatic hyperplasia and prostate cancer. The developing LUT is anatomically complex. By the time prostatic budding begins on 16.5 days post conception (dpc), numerous cell types are present. Vasculature, nerves and smooth muscle reside within the mesenchymal stroma(3). This stroma surrounds a multilayered epithelium and gives rise to the fetal prostate through androgen receptor-dependent paracrine signals(4). The identity of the stromal androgen receptor-responsive genes required for prostate development and the mechanism by which prostate ductal epithelium forms in response to these genes is not fully understood. The ability to precisely identify cell types and localize expression of specific factors within them is imperative to further understand prostate development. In situ hybridization (ISH) allows for localization of mRNAs within a tissue. Thus, this method can be used to identify pattern and timing of expression of signaling molecules and their receptors, thereby elucidating potential prostate developmental regulators. Here, we describe a high throughput ISH technique to identify mRNA expression patterns in the fetal mouse LUT using vibrating microtome-cut sections. This method offers several advantages over other ISH protocols. Performing ISH on thin sections adhered to a slide is technically difficult; cryosections frequently have poor structural quality while both cryosections and paraffin sections often result in weak signal resolution. Performing ISH on whole mount tissues can result in probe trapping. In contrast, our high throughput technique utilizes thick-cut sections that reveal detailed tissue architecture. Modified microfuge tubes allow easy handling of sections during the ISH procedure. A maximum of 4 mRNA transcripts can be screened from a single 17.5dpc LUT with up to 24 mRNA transcripts detected in a single run, thereby reducing cost and maximizing efficiency. This method allows multiple treatment groups to be processed identically and as a single unit, thereby removing any bias for interpreting data. Most pertinently for prostate researchers, this method provides a spatial and temporal location of low and high abundance mRNA transcripts in the fetal mouse urethra that gives rise to the prostate ductal network.
Brunskill, EW; Georgas, K; Rumballe, B; Little, MH; Potter, SS. PLoS ONE. vol. 6(9) 2011.
BACKGROUND: The podocyte is a remarkable cell type, which encases the capillaries of the kidney glomerulus. Although mesodermal in origin it sends out axonal like projections that wrap around the capillaries. These extend yet finer projections, the foot processes, which interdigitate, leaving between them the slit diaphragms, through which the glomerular filtrate must pass. The podocytes are a subject of keen interest because of their key roles in kidney development and disease. METHODOLOGY/PRINCIPAL FINDINGS: In this report we identified and characterized a novel transgenic mouse line, MafB-GFP, which specifically marked the kidney podocytes from a very early stage of development. These mice were then used to facilitate the fluorescent activated cell sorting based purification of podocytes from embryos at E13.5 and E15.5, as well as adults. Microarrays were then used to globally define the gene expression states of podocytes at these different developmental stages. A remarkable picture emerged, identifying the multiple sets of genes that establish the neuronal, muscle, and phagocytic properties of podocytes. The complete combinatorial code of transcription factors that create the podocyte was characterized, and the global lists of growth factors and receptors they express were defined. CONCLUSIONS/SIGNIFICANCE: The complete molecular character of the in vivo podocyte is established for the first time. The active molecular functions and biological processes further define their unique combination of features. The results provide a resource atlas of gene expression patterns of developing and adult podocytes that will help to guide further research of these incredible cells.
Harding, SD; Armit, C; Armstrong, J; Brennan, J; Cheng, Y; Haggarty, B; Houghton, D; Lloyd-MacGilp, S; Pi, X; Roochun, Y; Sharghi, M; Tindal, C; McMahon, AP; Gottesman, B; Little, MH; Georgas, K; Aronow, B; Potter, SS; Brunskill, EW; Southard-Smith, EM; Mendelsohn, C; Baldock, RA; Davies, JA; Davidson, D. Development. vol. 138(13), 2845–53. July 2011.
The GenitoUrinary Development Molecular Anatomy Project (GUDMAP) is an international consortium working to generate gene expression data and transgenic mice. GUDMAP includes data from large-scale in situ hybridisation screens (wholemount and section) and microarray gene expression data of microdissected, laser-captured and FACS-sorted components of the developing mouse genitourinary (GU) system. These expression data are annotated using a high-resolution anatomy ontology specific to the developing murine GU system. GUDMAP data are freely accessible at www.gudmap.org via easy-to-use interfaces. This curated, high-resolution dataset serves as a powerful resource for biologists, clinicians and bioinformaticians interested in the developing urogenital system. This paper gives examples of how the data have been used to address problems in developmental biology and provides a primer for those wishing to use the database in their own research.
Georgas, KM; Chiu, HS; Lesieur, E; Rumballe, BA; Little, MH. Dev Dyn. vol. 240(6), 1600–12. June 2011.
The metanephros is the functional organ in adult amniotes while the mesonephros degenerates. However, parallel tubulogenetic events are thought to exist between mesonephros and metanephros. Mesonephric tubules are retained in males and differentiate into efferent ducts of the male reproductive tract. By examining the murine mesonephric expression of markers of distinct stages and regions of metanephric nephrons during tubule formation and patterning, we provide further evidence to support this common morphogenetic mechanism. Renal vesicle, early proximal and distal tubule, loop of Henle, and renal corpuscle genes were expressed by mesonephric tubules. Vip, Slc6a20b, and Slc18a1 were male-specific. In contrast, mining of the GUDMAP database identified candidate late mesonephros-specific genes, 10 of which were restricted to the male. Among the male-specific genes are candidates for regulating ion/fluid balance within the efferent ducts, thereby regulating sperm maturation and genes marking tubule-associated neurons potentially critical for normal male reproductive tract function.
Comparative gene expression analysis of genital tubercle development reveals a putative appendicular Wnt7 network for the epidermal differentiation
Chiu, HS; Szucsik, JC; Georgas, KM; Jones, JL; Rumballe, BA; Tang, D; Grimmond, SM; Lewis, AG; Aronow, B; Lessard, JL; Little, MH. Developmental Biology. vol. 344(2), 1071–87. August 2010.
Here we describe the first detailed catalog of gene expression in the developing lower urinary tract (LUT), including epithelial and mesenchymal portions of the developing bladder, urogenital sinus, urethra, and genital tubercle (GT) at E13 and E14. Top compartment-specific genes implicated by the microarray data were validated using whole-mount in situ hybridization (ISH) over the entire LUT. To demonstrate the potential of this resource to implicate developmentally critical features, we focused on gene expression patterns and pathways in the sexually indeterminate, androgen-independent GT. GT expression patterns reinforced the proposed similarities between development of GT, limb, and craniofacial prominences. Comparison of spatial expression patterns predicted a network of Wnt7a-associated GT-enriched epithelial genes, including Gjb2, Dsc3, Krt5, and Sostdc1. Known from other contexts, these genes are associated with normal epidermal differentiation, with disruptions in Dsc3 and Gjb2 showing palmo-plantar keratoderma in the limb. We propose that this gene network contributes to normal foreskin, scrotum, and labial development. As several of these genes are known to be regulated by, or contain cis elements responsive to retinoic acid, estrogen, or androgen, this implicates this pathway in the later androgen-dependent development of the GT.
Rumballe, B; Georgas, K; Wilkinson, L; Little, MH. Pediatr Nephrol. vol. 25(6), 1005–16. June 2010.
The discipline of paediatric nephrology encompasses the congenital nephritic syndromes, renal dysplasias, neonatal renal tumours, early onset cystic disease, tubulopathies and vesicoureteric reflux, all of which arise due to defects in normal kidney development. Indeed, congenital anomalies of the kidney and urinary tract (CAKUT) represent 20-30% of prenatal anomalies, occurring in 1 in 500 births. Developmental biologists have studied the anatomical and morphogenetic processes involved in kidney development for the last five decades. However, with the advent of transgenic mice, the sequencing of the genome, improvements in mutation detection and the advent of functional genomics, our understanding of the molecular basis of kidney development has grown significantly. Here we discuss how the advent of new genetic and genomics approaches has added to our understanding of kidney development and paediatric renal disease, as well as identifying areas in which we are still lacking knowledge.
Mugford, JW; Yu, J; Kobayashi, A; McMahon, AP. Dev Biol. vol. 333(2), 312–23. September 2009.
The functional unit of the kidney is the nephron. During its organogenesis, the mammalian metanephric kidney generates thousands of nephrons over a protracted period of fetal life. All nephrons are derived from a population of self-renewing multi-potent progenitor cells, termed the cap mesenchyme. However, our understanding of the molecular and cellular mechanisms underlying nephron development is at an early stage. In order to identify factors involved in nephrogenesis, we performed a high-resolution, spatial profiling of a number of transcriptional regulators expressed within the cap mesenchyme and early developing nephron. Our results demonstrate novel, stereotypic, spatially defined cellular sub-domains within the cap mesenchyme, which may, in part, reflect induction of nephron precursors. These results suggest a hitherto unappreciated complexity of cell states that accompany the assembly of the metanephric kidney, likely reflecting diverse regulatory actions such as the maintenance and induction of nephron progenitors.
Georgas, K; Rumballe, B; Valerius, MT; Chiu, HS; Thiagarajan, RD; Lesieur, E; Aronow, B; Brunskill, EW; Combes, AN; Tang, D; Taylor, D; Grimmond, SM; Potter, SS; McMahon, AP; Little, MH. Dev Biol. vol. 332(2), 273–86. August 2009.
While nephron formation is known to be initiated by a mesenchyme-to-epithelial transition of the cap mesenchyme to form a renal vesicle (RV), the subsequent patterning of the nephron and fusion with the ureteric component of the kidney to form a patent contiguous uriniferous tubule has not been fully characterized. Using dual section in situ hybridization (SISH)/immunohistochemistry (IHC) we have revealed distinct distal/proximal patterning of Notch, BMP and Wnt pathway components within the RV stage nephron. Quantitation of mitoses and Cyclin D1 expression indicated that cell proliferation was higher in the distal RV, reflecting the differential developmental programs of the proximal and distal populations. A small number of RV genes were also expressed in the early connecting segment of the nephron. Dual ISH/IHC combined with serial section immunofluorescence and 3D reconstruction revealed that fusion occurs between the late RV and adjacent ureteric tip via a process that involves loss of the intervening ureteric epithelial basement membrane and insertion of cells expressing RV markers into the ureteric tip. Using Six2-eGFPCre x R26R-lacZ mice, we demonstrate that these cells are derived from the cap mesenchyme and not the ureteric epithelium. Hence, both nephron patterning and patency are evident at the late renal vesicle stage.
Combes, AN; Lesieur, E; Harley, VR; Sinclair, AH; Little, MH; Wilhelm, D; Koopman, P. Dev Dyn. vol. 238(5), 1033–41. May 2009.
Testis cords are specialized tubes essential for generation and export of sperm, yet the mechanisms directing their formation, and the regulation of their position, size, shape, and number remain unclear. Here, we use a novel fluorescence-based three-dimensional modeling approach to show that cords initially form as a network of irregular cell clusters that are subsequently remodeled to form regular parallel loops, joined by a flattened plexus at the mesonephric side. Variation in cord number and structure demonstrates that cord specification is not stereotypic, although cord alignment and diameter becomes relatively consistent, implicating compensatory growth mechanisms. Branched, fused, and internalized cords were commonly observed. We conclude that the tubule-like structure of testis cords arise through a novel form of morphogenesis consisting of coalescence, partitioning, and remodeling. The methods we describe are applicable to investigating defects in testis cord development in mouse models, and more broadly, studying morphogenesis of other tissues.
Brunskill, EW; Aronow, B; Georgas, K; Rumballe, B; Valerius, MT; Aronow, B; Kaimal, V; Jegga, AG; Yu, J; Grimmond, SM; McMahon, AP; Patterson, LT; Little, MH; Potter, SS. Dev Cell. vol. 15(5), 781–91. November 2008.
Kidney development is based on differential cell-type-specific expression of a vast number of genes. While multiple critical genes and pathways have been elucidated, a genome-wide analysis of gene expression within individual cellular and anatomic structures is lacking. Accomplishing this could provide significant new insights into fundamental developmental mechanisms such as mesenchymal-epithelial transition, inductive signaling, branching morphogenesis, and segmentation. We describe here a comprehensive gene expression atlas of the developing mouse kidney based on the isolation of each major compartment by either laser capture microdissection or fluorescence-activated cell sorting, followed by microarray profiling. The resulting data agree with known expression patterns and additional in situ hybridizations. This kidney atlas allows a comprehensive analysis of the progression of gene expression states during nephrogenesis, as well as discovery of potential growth factor-receptor interactions. In addition, the results provide deeper insight into the genetic regulatory mechanisms of kidney development.
Use of dual section mRNA in situ hybridisation/immunohistochemistry to clarify gene expression patterns during the early stages of nephron development in the embryo and in the mature nephron of the adult mouse kidney
Georgas, K; Rumballe, B; Wilkinson, L; Chiu, HS; Lesieur, E; Gilbert, T; Little, MH. Histochem Cell Biol. vol. 130(5), 927–42. November 2008.
The kidney is the most complex organ within the urogenital system. The adult mouse kidney contains in excess of 8,000 mature nephrons, each of which can be subdivided into a renal corpuscle and 14 distinct tubular segments. The histological complexity of this organ can make the clarification of the site of gene expression by in situ hybridisation difficult. We have defined a panel of seven antibodies capable of identifying the six stages of early nephron development, the tubular nephron segments and the components of the renal corpuscle within the embryonic and adult mouse kidney. We have analysed in detail the protein expression of Wt1, Calb1 Aqp1, Aqp2 and Umod using these antibodies. We have then coupled immunohistochemistry with RNA in situ hybridisation in order to precisely identify the expression pattern of different genes, including Wnt4, Umod and Spp1. This technique will be invaluable for examining at high resolution, the structure of both the developing and mature nephron where standard in situ hybridisation and histological techniques are insufficient. The use of this technique will enhance the expression analyses of genes which may be involved in nephron formation and the function of the mature nephron in the mouse.
Rumballe, B; Georgas, K; Little, MH. CSH Protoc. vol. 2008 July 2008.
Section in situ hybridization (SISH) is a high-resolution tool used to analyze gene expression patterns. This protocol utilizes the Tecan Freedom EVO150 platform to perform high-throughput SISH on paraffin sections to detect mRNA with a digoxigenin (DIG)-labeled probe. The slide is mounted and imaged before performing immunohistochemistry (IHC) on the same section. The dual reaction enables a marker of protein expression to be localized on the same section as the mRNA and facilitates more accurate annotation of the gene expression.
McMahon, AP; Aronow, B; Davidson, DR; Davies, JA; Gaido, KW; Grimmond, SM; Lessard, JL; Little, MH; Potter, SS; Wilder, EL; Zhang, P; GUDMAP, Project. J Am Soc Nephrol. vol. 19(4), 667–71. April 2008.
In late 2004, an International Consortium of research groups were charged with the task of producing a high-quality molecular anatomy of the developing mammalian urogenital tract (UGT). Given the importance of these organ systems for human health and reproduction, the need for a systematic molecular and cellular description of their developmental programs was deemed a high priority. The information obtained through this initiative is anticipated to enable the highest level of basic and clinical research grounded on a 21st-century view of the developing anatomy. There are three components to the Genitourinary Developmental Molecular Anatomy Project GUDMAP; all of these are intended to provide resources that support research on the kidney and UGT. The first provides ontology of the cell types during UGT development and the molecular hallmarks of those cells as discerned by a variety of procedures, including in situ hybridization, transcriptional profiling, and immunostaining. The second generates novel mouse strains. In these strains, cell types of particular interest within an organ are labeled through the introduction of a specific marker into the context of a gene that exhibits appropriate cell type or structure-specific expression. In addition, the targeting construct enables genetic manipulation within the cell of interest in many of the strains. Finally, the information is annotated, collated, and promptly released at regular intervals, before publication, through a database that is accessed through a Web portal. Presented here is a brief overview of the Genitourinary Developmental Molecular Anatomy Project effort.
Little, MH; Brennan, J; Georgas, K; Davies, JA; Davidson, DR; Baldock, RA; Beverdam, A; Bertram, JF; Capel, B; Chiu, HS; Clements, D; Cullen-McEwen, L; Fleming, J; Gilbert, T; Herzlinger, D; Houghton, D; Kaufman, MH; Kleymenova, E; Koopman, PA; Lewis, AG; McMahon, AP; Mendelsohn, C; Mitchell, EK; Rumballe, BA; Sweeney, DE; Valerius, MT; Yamada, G; Yang, Y; Yu, J. Gene Expr Patterns. vol. 7(6), 680–99. June 2007.
Cataloguing gene expression during development of the genitourinary tract will increase our understanding not only of this process but also of congenital defects and disease affecting this organ system. We have developed a high-resolution ontology with which to describe the subcompartments of the developing murine genitourinary tract. This ontology incorporates what can be defined histologically and begins to encompass other structures and cell types already identified at the molecular level. The ontology is being used to annotate in situ hybridisation data generated as part of the Genitourinary Development Molecular Anatomy Project (GUDMAP), a publicly available data resource on gene and protein expression during genitourinary development. The GUDMAP ontology encompasses Theiler stage (TS) 17-27 of development as well as the sexually mature adult. It has been written as a partonomic, text-based, hierarchical ontology that, for the embryological stages, has been developed as a high-resolution expansion of the existing Edinburgh Mouse Atlas Project (EMAP) ontology. It also includes group terms for well-characterised structural and/or functional units comprising several sub-structures, such as the nephron and juxtaglomerular complex. Each term has been assigned a unique identification number. Synonyms have been used to improve the success of query searching and maintain wherever possible existing EMAP terms relating to this organ system. We describe here the principles and structure of the ontology and provide representative diagrammatic, histological, and whole mount and section RNA in situ hybridisation images to clarify the terms used within the ontology. Visual examples of how terms appear in different specimen types are also provided.