Adult Gli2+/-;Gli3Δ699/+ Male and Female Mice Display a Spectrum of Genital Malformation

Streamlined identification of clinically and functionally relevant genetic regulators of lower-tract urogenital development

Congenital anomalies of the lower genitourinary (LGU) tract are frequently comorbid due to genetically linked developmental pathways, and are among the most common yet most socially stigmatized congenital phenotypes. Genes involved in sexual differentiation are prime candidates for developmental anomalies of multiple LGU organs, but insufficient prospective screening tools have prevented the rapid identification of causative genes. Androgen signaling is among the most influential modulators of LGU development. The present study uses SpDamID technology in vivo to generate a comprehensive map of the pathways actively regulated by the androgen receptor (AR) in the genitalia in the presence of the p300 coactivator, identifying wingless/integrated (WNT) signaling as a highly enriched AR-regulated pathway in the genitalia. Transcription factor (TF) hits were then assayed for sexually dimorphic expression at two critical time points and also cross-referenced to a database of clinically relevant copy number variations to identify 252 TFs exhibiting copy variation in patients with LGU phenotypes. A subset of 54 TFs was identified for which LGU phenotypes are statistically overrepresented as a proportion of total observed phenotypes. The 252 TF hitlist was then subjected to a functional screen to identify hits whose silencing affects genital mesenchymal growth rates. Overlap of these datasets results in a refined list of 133 TFs of both functional and clinical relevance to LGU development, 31 of which are top priority candidates, including the well-documented renal progenitor regulator, Sall1. Loss of Sall1 was examined in vivo and confirmed to be a powerful regulator of LGU development.

Prenatal exposure to diethylstilbestrol has long-lasting, transgenerational impacts on fertility and reproductive development

Significant decreases in fertility have been observed over the past 50 years, with female conception rates dropping by 44% and male sperm counts decreasing by over 50%. This dramatic decrease in fertility can be attributed in part to our increasing exposure to endocrine disrupting chemicals (EDCs). Diethylstilbestrol (DES) is an estrogenic EDC that was prescribed to millions of pregnant women between 1940 and 1970 and resulted in detrimental reproductive effects in the offspring that were exposed in utero. Women who were exposed to DES in utero experienced higher rates of infertility, pregnancy complications, and reproductive cancers. Alarmingly, there is evidence to suggest that these effects may persist in the grandchildren and great grandchildren of exposed women. To define the transgenerational reproductive impacts in females following exposure to DES, gestating mice were exposed to DES and the effects monitored in the female descendants across 3 generations. There was a trend for reduced pregnancy rate and fertility index seen across the generations and moreover, the anogenital distance (AGD) was significantly reduced up until the third, unexposed generation. The onset of puberty was also significantly affected, with the timing of vaginal opening occurring significantly earlier in DES descendants. These results indicate a transgenerational effect of DES on multiple reproductive parameters including fertility, timing of puberty, and AGD. These data have significant implications for more than 50 million DES descendants worldwide as well as raising concerns for the ongoing health impacts caused by exposures to other estrogenic EDCs which are pervasive in our environment.

A study on etiology of incontinence in double knockout mouse model

INTRODUCTION AND OBJECTIVE

Stress urinary incontinence is of concern in both pediatric and adult population. Double mutant GLI family zinc finger Gli2^+/-; Gli3^Δ699/+ murine model of stress incontinence has been recently developed as a reliable model which does not require surgical manipulation to create incontinence and is shown to survive to adulthood. The aim of this study was to establish the etiology of incontinence in the double mutant Gli2^+/-; Gli3^Δ699/+ mice.

STUDY DESIGN

We used 13 cluster of differentiation 1 (CD-1) mice (7-9 weeks) for demonstration of histology of the bladder and urethra. There were 3 Wild Gli2^+/- females, 2 Wild Gli2^+/- males, 4 Gli2^+/-;Gli3^Δ699/+ females and 4 Gli2^+/-;Gli3^Δ699/+ males. The Wild Gli2^+/- mice served as the control group and Gli2^+/-;Gli3^Δ699/+ mice served as the test group. Additionally, eight 16.5 days mice (2 each of Wild Gli2^+/- females, Wild Gli2^+/- males, double knockout (DKO) Gli2^+/-;Gli3^Δ699/+ females and Gli2^+/-;Gli3^Δ699/+ males) were used to assess the histology of the spinal cord. The gross appearance of bladder and urethra was studied using ink injection assays. Immunohistochemistry was done for smooth muscle actin and cytokeratin.

RESULTS

Gross and histologic appearance confirmed the previously reported widening of bladder outlet and hypoplasia of smooth muscles in female urethra and also established them in the male urethra of Gli2^+/-;Gli3^Δ699/+ mice compared to Gli2^+/- mice. The double knockout mice were smaller than the Gli2 mice (5.2 vs 6.1 cm, p = 0.002). Immunohistochemistry demonstrated epithelial hyperplasia and smooth muscle hypoplasia. Additionally, there was prostatic hypoplasia in the Gli2^+/-;Gli3^Δ699/+ male mice. The spinal cord length for body size appeared comparable between the Gli2^+/- and Gli2^+/-;Gli3^Δ699/+ mice but histological evaluation revealed abnormal development of the caudal end of the vertebral body with premature termination of the spinal cord (Figure).

DISCUSSION

The histological changes in the bladder neck and urethra were consistent to those previously reported. While previous report described the findings in female mice only, we confirmed that these findings are also present in males as well as prostatic hypoplasia, a possible additional factor leading to stress incontinence. The most important finding in the present study however, was the detection of premature termination of spinal cord in the DKO Gli2^+/-; Gli3^Δ699/+ mice which has not been reported previously and is likely a major contributor to incontinence in this model.

CONCLUSION

The incontinence in male as well as female Gli2^+/-; Gli3^Δ699/+ mice is due to both myogenic and neurogenic involvement. These double knockout mice are a valuable model of stress incontinence related to neurogenic bladder due to low outlet resistance.

Development of an in-vitro high-throughput screening system to identify modulators of genitalia development

Sexually dimorphic outgrowth and differentiation of the embryonic genital tubercles (GTs) give rise to the penis in males and the clitoris in females. Defects in androgen production or in response to androgen signaling can lead to various congenital penile anomalies in both mice and humans. Due to lack of a high-throughput screening system, identification of crucial regulators of GT sexual differentiation has been slow. To overcome this research barrier, we isolated embryonic GT mesenchymal (GTme) cells to model genitalia growth and differentiation in vitro. Using either a mechanical or fluorescence-activated cell sorting-assisted purification method, GTme cells were isolated and assayed for their proliferation using a microscopy and image analysis system, on a single cell level over time. Male and female GTme cells inherently exhibit different cellular dynamics, consistent with their in-vivo behaviors. This system allows for the rapid quantitative analyses of numerous drug treatments, and enables the discovery of potential genetic modulators of GT morphogenesis on a large scale. Using this system, we completed a 438-compound library screen and identified 82 kinase inhibitor hits. In mice, in-utero exposure to one such candidate kinase inhibitor, Cediranib, resulted in embryos with severe genitalia defects, especially in males. Gene silencing by RNAi was optimized in this system, laying the foundation for future larger-scale genetic screenings. These findings demonstrate the power of this novel high-throughput system to rapidly and successfully identify modulators of genitalia growth and differentiation, expanding the toolbox for the study of functional genomics and environmental factors.

Cholesterol Contributes to Male Sex Differentiation Through Its Developmental Role in Androgen Synthesis and Hedgehog Signaling

Two specialized functions of cholesterol during fetal development include serving as a precursor to androgen synthesis and supporting hedgehog (HH) signaling activity. Androgens are produced by the testes to facilitate masculinization of the fetus. Recent evidence shows that intricate interactions between the HH and androgen signaling pathways are required for optimal male sex differentiation and defects of either can cause birth anomalies indicative of 46,XY male variations of sex development (VSD). Further, perturbations in cholesterol synthesis can cause developmental defects, including VSD, that phenocopy those caused by disrupted androgen or HH signaling, highlighting the functional role of cholesterol in promoting male sex differentiation. In this review, we focus on the role of cholesterol in systemic androgen and local HH signaling events during fetal masculinization and their collective contributions to pediatric VSD.

GLI3 resides at the intersection of hedgehog and androgen action to promote male sex differentiation

Urogenital tract abnormalities are among the most common congenital defects in humans. Male urogenital development requires Hedgehog-GLI signaling and testicular hormones, but how these pathways interact is unclear. We found that Gli3^XtJ mutant mice exhibit cryptorchidism and hypospadias due to local effects of GLI3 loss and systemic effects of testicular hormone deficiency. Fetal Leydig cells, the sole source of these hormones in developing testis, were reduced in numbers in Gli3^XtJ testes, and their functional identity diminished over time. Androgen supplementation partially rescued testicular descent but not hypospadias in Gli3^XtJ mutants, decoupling local effects of GLI3 loss from systemic effects of androgen insufficiency. Reintroduction of GLI3 activator (GLI3A) into Gli3^XtJ testes restored expression of Hedgehog pathway and steroidogenic genes. Together, our results show a novel function for the activated form of GLI3 that translates Hedgehog signals to reinforce fetal Leydig cell identity and stimulate timely INSL3 and testosterone synthesis in the developing testis. In turn, exquisite timing and concentrations of testosterone are required to work alongside local GLI3 activity to control development of a functionally integrated male urogenital tract.

Disorders in male sex differentiation (DSD) are among the most common defects in all live births, yet in many cases, pediatric patient families are reluctant to address the issue and endure lifelong consequences. Urogenital tract development, as in many organ systems, depends on exquisite timing among layers of a number of signaling pathways. Here, we show that interactions between the hedgehog and androgen signaling pathways are required for the development of internal and external male sex characteristics, but results for each tissue is distinct. This new knowledge will aid in discovering the means by which congenital malformations might occur, identify potential developmental targets that might be vulnerable to environmental exposures, and promote new ideas for how they might be prevented.

Hedgehog Signaling for Urogenital Organogenesis and Prostate Cancer: An Implication for the Epithelial-Mesenchyme Interaction (EMI)

Hedgehog (Hh) signaling is an essential growth factor signaling pathway especially in the regulation of epithelial-mesenchymal interactions (EMI) during the development of the urogenital organs such as the bladder and the external genitalia (EXG). The Hh ligands are often expressed in the epithelia, affecting the surrounding mesenchyme, and thus constituting a form of paracrine signaling. The development of the urogenital organ, therefore, provides an intriguing opportunity to study EMI and its relationship with other pathways, such as hormonal signaling. Cellular interactions of prostate cancer (PCa) with its neighboring tissue is also noteworthy. The local microenvironment, including the bone metastatic site, can release cellular signals which can affect the malignant tumors, and vice versa. Thus, it is necessary to compare possible similarities and divergences in Hh signaling functions and its interaction with other local growth factors, such as BMP (bone morphogenetic protein) between organogenesis and tumorigenesis. Additionally, this review will discuss two pertinent research aspects of Hh signaling: (1) the potential signaling crosstalk between Hh and androgen signaling; and (2) the effect of signaling between the epithelia and the mesenchyme on the status of the basement membrane with extracellular matrix structures located on the epithelial-mesenchymal interface.

A novel long non-coding RNA, Leat1, causes reduced anogenital distance and fertility in female mice

Defective anorectal and urogenital malformations are some of the most severe congenital anomalies encountered in children. Only a few molecular cues have been identified in early formation of the female urogenital system. Here we describe a novel long non-coding RNA molecule known as Leat1 (long non-coding RNA, EphrinB2 associated transcript 1). This lncRNA is syntenic with EfnB2 (which encodes EphrinB2) and expressed during embryonic development of the genital tubercle. While lncRNAs have varied functions, many are known to regulate their neighbouring genes. Eph/Ephrin bidirectional signaling molecules mediate many patterning pathways in early embryonic development, including cloacal septation and urethral development. Here we investigate the role of Leat1 and its possible regulation of EphrinB2 during development of the female reproductive tract. We show that a loss of Leat1 leads to reduced EfnB2 expression in the developing female genital tubercle, reduced anogenital distance and decreased fertility.

Temporal, spatial, and genetic regulation of external genitalia development

Fertilization requires the physical combination of gametes, and terrestrial mammals necessitated the evolution of genitalia capable of successfully completing the fertilization process in a non-aqueous environment. Thus, the male mammalian external genitalia evolved as an outgrowth from the body, an appendage sufficient to fertilize eggs housed deep inside the female. In this way, sexual dimorphism of mammalian genitalia became highly pronounced. This highly complex evolutionary divergence both from aqueous fertilization, as well as divergence between the sexes of terrestrial mammals, required exquisitely coordinated, novel patterns of gene expression to regulate the spatial and temporal events governing external genitalia development. Recent studies delineating the genetic regulation of external genitalia development, largely focusing on development of the murine genital tubercle, have vastly enlightened the field of reproductive developmental biology. Murine homologs of human genes have been selectively deleted in the mouse, either in the whole body or using tissue-specific and temporally-specific genetic drivers. The defects in outgrowth and urethral tubularization subsequent to the deletion of specific genes in the developing murine external genitalia delineates which genes are required in which compartments and at what times. This review details how these murine genetic models have created a somewhat modest but rapidly growing library of knowledge detailing the spatial-temporal genetic regulation of external genitalia development.

GLI3 repressor but not GLI3 activator is essential for mouse eye patterning and morphogenesis

Since 1967, it is known that the loss of GLI3 causes very severe defects in murine eye development. GLI3 is able to act as a transcriptional activator (GLI3-A) or as a transcriptional repressor (GLI3-R). Soon after the discovery of these GLI3 isoforms, the question arose which of the different isoforms is involved in eye formation - GLI3-A, GLI3-R or even both. For several years, this question remained elusive. By analysing the eye morphogenesis of Gli3^XtJ/XtJ mouse embryos that lack GLI3-A and GLI3-R and of Gli3^Δ699/Δ699 mouse embryos in which only GLI3-A is missing, we revealed that GLI3-A is dispensable in vertebrate eye formation. Remarkably, our study shows that GLI3-R is sufficient for the creation of morphologically normal eyes although the molecular setup deviates substantially from normality. In depth-investigations elucidated that GLI3-R controls numerous key players in eye development and governs lens and retina development at least partially via regulating WNT/β-CATENIN signalling.