Cell lineages of the early human gonad commit to one of the two mutually antagonistic organogenetic fates, the testis or the ovary. Some individuals with a 46,XX karyotype develop testes or ovotestes (testicular or ovotesticular disorder of sex development; TDSD/OTDSD), due to the presence of the testis-determining gene, SRY. Other rare complex syndromic forms of TDSD/OTDSD are associated with mutations in pro-ovarian genes that repress testis development (e.g. WNT4); however, the genetic cause of the more common non-syndromic forms is unknown. Steroidogenic factor-1 (known as NR5A1) is a key regulator of reproductive development and function. Loss-of-function changes in NR5A1 in 46,XY individuals are associated with a spectrum of phenotypes in humans ranging from a lack of testis formation to male infertility. Mutations in NR5A1 in 46,XX women are associated with primary ovarian insufficiency, which includes a lack of ovary formation, primary and secondary amenorrhoea as well as early menopause. Here, we show that a specific recurrent heterozygous missense mutation (p.Arg92Trp) in the accessory DNA-binding region of NR5A1 is associated with variable degree of testis development in 46,XX children and adults from four unrelated families. Remarkably, in one family a sibling raised as a girl and carrying this NR5A1 mutation was found to have a 46,XY karyotype with partial testicular dysgenesis. These unique findings highlight how a specific variant in a developmental transcription factor can switch organ fate from the ovary to testis in mammals and represents the first missense mutation causing isolated, non-syndromic 46,XX testicular/ovotesticular DSD in humans.

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Human sex determination (SD) involves complex mutually antagonistic genetic interactions of testis‐ and ovary‐determining pathways. For many years, both male and female SD were considered to be regulated by a linear cascade of pro‐male and pro‐female genes, respectively; however, it has become clear that male and female development is achieved through the repression of the alternative state. A gene determining the formation of a testis may function by repressing the female state and vice versa. Uniquely in development, SD is achieved by suppression of the alternate fate and maintained in adulthood by a mutually antagonistic double‐repressive pathway. Here, we review genetic data generated through large‐scale sequencing approaches that are changing our view of how this system works, including the recently described recurrent NR5A1 p.R92W mutation associated with testis development in 46,XX children. We also review some of the unique challenges in the field to establish that mutations, such as this are pathogenic. The impending surge of new genetic data on human SD from sequencing projects will create opportunities for the development of mechanistic models that will clarify how the system operates and importantly provide data to understand how selection and developmental processes interact to direct the evolution of SD across species.

SignificanceSex determination involves antagonistic interactions between the testis-determining (SRY-SOX9-FGF9) and ovary-promoting (RSPO1-WNT/β-catenin-FOXL2) pathways, but the underlying molecular mechanisms remain unclear. We show that ZNRF3, an E3 ubiquitin ligase that inhibits WNT signaling and is a direct target of RSPO1-mediated membrane clearance, is testis-determining in mice. Testis determination defects in the absence of ZNRF3 arise due to ectopic canonical WNT signaling in XY gonads at the sex-determining stage. We identify human ZNRF3 sequence variants in cases of 46,XY disorders of sex development with XY female presentation. In vitro functional assays show that these variants disrupt ZNRF3 function. Our data reveal a sex-determining role for ZNRF3 and indicate that interactions between ZNRF3 and RSPO1 regulate mammalian sex determination.

Purpose: XY individuals with disorders/differences of sex development (DSD) are characterized by reduced androgenization caused, in some children, by gonadal dysgenesis or testis regression during fetal development. The genetic etiology for most patients with 46,XY gonadal dysgenesis and for all patients with testicular regression syndrome (TRS) is unknown. Methods: We performed exome and/or Sanger sequencing in 145 individuals with 46,XY DSD of unknown etiology including gonadal dysgenesis and TRS. Results: Thirteen children carried heterozygous missense pathogenic variants involving the RNA helicase DHX37, which is essential for ribosome biogenesis. Enrichment of rare/novel DHX37 missense variants in 46,XY DSD is highly significant compared with controls (P value = 5.8 × 10 −10). Five variants are de novo (P value = 1.5 × 10 −5). Twelve variants are clustered in two highly conserved functional domains and were specifically associated with gonadal dysgenesis and TRS. Consistent with a role in early testis development, DHX37 is expressed specifically in somatic cells of the developing human and mouse testis. Conclusion: DHX37 pathogenic variants are a new cause of an autosomal dominant form of 46,XY DSD, including gonadal dysgenesis and TRS, showing that these conditions are part of a clinical spectrum. This raises the possibility that some forms of DSD may be a ribosomopathy.

Emerging evidence from murine studies suggests that mammalian sex determination is the outcome of an imbalance between mutually antagonistic male and female regulatory networks that canalize development down one pathway while actively repressing the other. However, in contrast to testis formation, the gene regulatory pathways governing mammalian ovary development have remained elusive. We performed exome or Sanger sequencing on 79 46,XX SRY-negative individuals with either unexplained virilization or with testicular/ovotesticular disorders/differences of sex development (TDSD/OTDSD). We identified heterozygous frameshift mutations in NR2F2, encoding COUP-TF2, in three children. One carried a c.103_109delGGCGCCC (p.Gly35Argfs∗75) mutation, while two others carried a c.97_103delCCGCCCG (p.Pro33Alafs∗77) mutation. In two of three children the mutation was de novo. All three children presented with congenital heart disease (CHD), one child with congenital diaphragmatic hernia (CDH), and two children with blepharophimosis-ptosis-epicanthus inversus syndrome (BPES). The three children had androgen production, virilization of external genitalia, and biochemical or histological evidence of testicular tissue. We demonstrate a highly significant association between the NR2F2 loss-of-function mutations and this syndromic form of DSD (p = 2.44 × 10−8). We show that COUP-TF2 is highly abundant in a FOXL2-negative stromal cell population of the fetal human ovary. In contrast to the mouse, these data establish COUP-TF2 as a human “pro-ovary” and “anti-testis” sex-determining factor in female gonads. Furthermore, the data presented here provide additional evidence of the emerging importance of nuclear receptors in establishing human ovarian identity and indicate that nuclear receptors may have divergent functions in mouse and human biology.

FOXL2, a winged-helix/forkhead domain transcription factor, is a key gene involved in the differentiation and biological functions of the ovary. In a recent transcriptomic analysis, we found that FOXL2 expression in bovine caruncular endometrium was different from that in intercaruncular endometrium. In order to gain new insights into FOXL2 in this tissue, we determined the expression of this transcription factor during the estrous cycle and the establishment of pregnancy in cattle. The endometrial expression of FOXL2 did not vary during maternal recognition of pregnancy (Days 16-20). Using an in vivo bovine model and primary cell cultures, we showed that FOXL2 was not an interferon-tau target gene. Both FOXL2 transcript and protein were expressed from Day 5 to Day 20 of the estrous cycle, and their levels showed a significant increase during the luteolytic phase. A 2-day progesterone supplementation in heifers led to a clear down-regulation of FOXL2 protein levels, suggesting the negative impact of progesterone on FOXL2 expression. Immunohistochemistry data revealed the localization of FOXL2 in endometrial stromal and glandular cells. FOXL2 subcellular distribution was shown to be nuclear in endometrial samples collected during the luteolytic period, while it was not detected in nuclei during the luteal phase and at implantation. Collectively, our findings provide the first evidence that FOXL2 is involved in the regulation of endometrial tissue physiology.

Sex determination in mammals is governed by antagonistic interactions of two genetic pathways, imbalance in which may lead to disorders/differences of sex development (DSD) in human. Among 46,XX individuals with testicular DSD (TDSD) or ovotesticular DSD (OTDSD), testicular tissue is present in the gonad. Although the testis-determining geneSRYis present in many cases, the etiology is unknown in mostSRY-negative patients. We performed exome sequencing on 78 individuals with 46,XX TDSD/OTDSD of unknown genetic etiology and identified seven (8.97%) with heterozygous variants affecting the fourth zinc finger (ZF4) of Wilms’ tumor 1 (WT1) (p.Ser478Thrfs*17, p.Pro481Leufs*15, p.Lys491Glu, p.Arg495Gln [x3], p.Arg495Gly). The variants were de novo in six families (P= 4.4 × 10−6), and the incidence of WT1 variants in 46,XX DSD is enriched compared to control populations (P< 1.8 × 10−4). The introduction of ZF4 mutants into a human granulosa cell line resulted in up-regulation of endogenous Sertoli cell transcripts andWt1Arg495Gly/Arg495GlyXX mice display masculinization of the fetal gonads. The phenotype could be explained by the ability of the mutated proteins to physically interact with and sequester a key pro-ovary factor β-CATENIN, which may lead to up-regulation of testis-specific pathway. Our data show that unlike previous association of WT1 and 46,XY DSD, ZF4 variants of WT1 are a relatively common cause of 46,XX TDSD/OTDSD. This expands the spectrum of phenotypes associated with WT1 variants and shows that the WT1 protein affecting ZF4 can function as a protestis factor in an XX chromosomal context.