Project description:Gonadal sex differentiation – testis versus ovary formation – is a fundamental process required for reproduction and evolution. Reflecting this importance, the embryonic gonads of vertebrate species comprise the same key cell types; germ cells, supporting cells and interstitial steroidogenic cells. Remarkably, the genetic triggers for gonadal sex differentiation vary across species (the SRY gene in mammals, DMRT1 in birds and some turtles, temperature in many reptiles, AMH and various other genes in fishes). Despite this variation, the cell biology of gonadal development was long thought to be largely conserved. Here, we present a comprehensive analysis of gonadal sex differentiation, using the chicken embryo as a model and considering the entire gonad. We sampled over 30,000 cells across several developmental stages, prior, during and after the onset of gonadal sex differentiation. The data provide several new insights into cell lineage specification during vertebrate gonadogenesis. Combining lineage tracing with single cell transcriptomics, the data show that somatic supporting cells of the embryonic chicken gonad do not derive from the coelomic epithelium, in contrast to other vertebrates studied. Instead, the early somatic precursors cells of the gonads in both sexes derive from a DMRT1+/PAX2+/WNT4+/OSR1+ mesenchymal cell population. In particular, PAX2 marks immigrating mesenchymal cells that give rise to the supporting cell lineage. We find a greater complexity of gonadal cell types than previously thought, including the identification of two distinct sub-populations of Sertoli cells in developing testes, and derivation of embryonic steroidogenic cells from a differentiated supporting cell lineage. We provide significantly improved resolution of gonadal cell types and identify several new gonadal marker genes. Altogether, these results indicate that, just as the genetic trigger for sex differs across vertebrate groups, cell lineage specification in the gonad may also vary substantially.
Project description:Sex determination in mammals hinges on a cell fate decision in the fetal bipotential gonad between male Sertoli cells and female granulosa cells. While this decision normally is permanent, loss of key cell fate regulators such as the transcription factors Dmrt1 and Foxl2 can cause postnatal transdifferentiation from Sertoli to granulosa-like or vice versa. Here we examine the mechanism of transdifferentiation in mice carrying either a null mutation of Dmrt1 or a point mutation, R111G, that alters the DNA binding motif and causes human XY gonadal dysgenesis and sex reversal. We first define genes misexpressed during transdifferentiation and then show that female transcriptional regulators driving transdifferentiation in the mutant XY gonad (ESR2, LRH1, FOXL2) bind chromatin sites related to those normally bound in the XX ovary. We then define gene expression changes at the onset of transdifferentiation and abnormal chromatin compartments that may help destabilize cell fate and initiate transdifferentiation. We model the R111G mutation in mice and show that it causes dominant gonadal dysgenesis, analogous to its human phenotype but less severe. We show that R111G partially feminizes the testicular transcriptome and causes dominant disruption of DMRT1 binding specificity in vivo. These data help illuminate how transdifferentiation occurs when sexual cell fate maintenance is disrupted and identify chromatin sites and transcripts that may play key roles in the transdifferentiation process.
Project description:Foxl2 is a forkhead transcription factor essential for proper reproductive function in females. It is expressed in the somatic cell population of the gonad (granulosa cells) which forms the follicles of the ovary, the structures responsible for embedding and nurturing the oocytes during their development. FOXL2 directly regulate the aromatase that synthesizes estrogens CYP19A1, thus promoting female differentiation, as well as acting as a repressor of the male factors SOX9 and DMRT1.Expression is also found in the eyelids, pituitary gland and uterus. In the goat, frog and many fish species FOXL2 is a sex-determining gene which, when deleted, leads to female-to-male sex reversal.
Project description:Transcription factors related to the insect sex determination gene Doublesex (DMRT proteins) control sex determination and/or sexual differentiation in diverse metazoans. They also are implicated in transitions between sex-determining mechanisms during vertebrate evolution. In mice Dmrt1 is required for male gonadal differentiation in somatic cells and germ cells. DMRT1 also maintains male gonadal sex: its loss, even in adults, can trigger sexual fate reprogramming in which male Sertoli cells transdifferentiate into their female equivalents - granulosa cells - and testicular tissue reorganizes to a more ovarian morphology. Here we use a conditional Dmrt1 transgene to show that Dmrt1 is not only necessary but also sufficient to specify male cell identity in the mouse gonad. DMRT1 expression in the ovary silenced the female sex-maintenance gene Foxl2 and reprogrammed juvenile and adult granulosa cells into Sertoli-like cells, triggering formation of structures resembling male seminiferous tubules. DMRT1 can silence Foxl2 even in the absence of the testis-determining genes Sox8 and Sox9. mRNA profiling found that DMRT1 activates many testicular genes and downregulates ovarian genes and single cell RNA-seq in transdifferentiating cells identified dynamically expressed candidate mediators of this process. Strongly upregulated genes were highly enriched on chromosome X, consistent with sexually antagonistic functions. This study provides an in vivo example of single gene reprogramming of cell sexual identity. Our findings suggest a reconsideration of mechanisms involved in human disorders of sexual development (DSD) and empirically support evolutionary models where loss or gain of Dmrt1 function promotes establishment of new vertebrate sex determination systems. RNA-Seq (3 conditions, 2 replicates per condition) and Single Cell RNA-Seq (68 individual cells and 1 bulk cell sample)
Project description:Dmrt1 is a highly conserved transcription factor, which is critically involved in regulation of gonad development of vertebrates. In medaka a duplicate of dmrt1, acting as master sex-determining gene, has a tightly timely and locally patterned gonadal expression pattern. In addition to transcriptional regulation, a sequence motif in the 3’ UTR (D3U-box) was shown to mediate transcript stability of dmrt1 mRNAs from medaka and other vertebrates. We show here that in medaka two RNA-binding proteins with antagonizing properties competitively target this D3U-box, promoting either RNA stabilization in germ cells or degradation in the soma. Such evolutionary conservation of the D3U-box motif within the dmrt1 genes and among genomes of metazoans together with preserved expression patterns of the targeting RNA binding proteins in subsets of germ cells, suggest this new mechanism for controlling RNA stability is not restricted to fishes, but might also apply to other vertebrates.
Project description:Transcription factors related to the insect sex determination gene Doublesex (DMRT proteins) control sex determination and/or sexual differentiation in diverse metazoans. They also are implicated in transitions between sex-determining mechanisms during vertebrate evolution. In mice Dmrt1 is required for male gonadal differentiation in somatic cells and germ cells. DMRT1 also maintains male gonadal sex: its loss, even in adults, can trigger sexual fate reprogramming in which male Sertoli cells transdifferentiate into their female equivalents - granulosa cells - and testicular tissue reorganizes to a more ovarian morphology. Here we use a conditional Dmrt1 transgene to show that Dmrt1 is not only necessary but also sufficient to specify male cell identity in the mouse gonad. DMRT1 expression in the ovary silenced the female sex-maintenance gene Foxl2 and reprogrammed juvenile and adult granulosa cells into Sertoli-like cells, triggering formation of structures resembling male seminiferous tubules. DMRT1 can silence Foxl2 even in the absence of the testis-determining genes Sox8 and Sox9. mRNA profiling found that DMRT1 activates many testicular genes and downregulates ovarian genes and single cell RNA-seq in transdifferentiating cells identified dynamically expressed candidate mediators of this process. Strongly upregulated genes were highly enriched on chromosome X, consistent with sexually antagonistic functions. This study provides an in vivo example of single gene reprogramming of cell sexual identity. Our findings suggest a reconsideration of mechanisms involved in human disorders of sexual development (DSD) and empirically support evolutionary models where loss or gain of Dmrt1 function promotes establishment of new vertebrate sex determination systems.
Project description:Mammalian sexual development commences when fetal bipotential progenitor cells adopt male Sertoli (in XY) or female granulosa (in XX) gonadal cell fates. Differentiation of these cells involves extensive divergence in chromatin state and gene expression, reflecting distinct roles in sexual differentiation and gametogenesis. Surprisingly, differentiated gonadal cell fates require active maintenance through postnatal life to prevent sexual transdifferentiation and female cell fate can be reprogrammed by ectopic expression of the sex regulator DMRT1. Here we examine how DMRT1 reprograms granulosa cells to Sertoli-like cells in vivo and in culture. We define postnatal granulosa- and Sertoli-biased gene expression programs and identify cell type-biased three-dimensional chromatin contacts and differentially accessible chromatin regions (DARs) associated with differentially expressed genes. Using a conditional transgene we find DMRT1 only partially reprograms the ovarian transcriptome in the absence of SOX9 and its paralog SOX8, indicating that these factors functionally cooperate with DMRT1. ATAC-seq and ChIP-seq show that DMRT1 induces formation of many DARs that it binds with SOX9, and DMRT1 is required for binding of SOX9 at most of these sites. We suggest that DMRT1 can act as a pioneer factor to open chromatin and allow binding of SOX9, which then cooperates with DMRT1 to reprogram sexual cell fate.
Project description:Spermatogonial stem cells (SSCs) have pluripotent potential. However, frequency of pluripotent cell derivation is low and the mechanism of culture-induced reprogramming remains unknown. Here we report that epigenetic instability of germline stem (GS) cells, cultured SSCs, induces pluripotent cell derivation. GS cells undergo DNA demethylation in H19 differentially methylated region under low-density culture. When H19 demethylation was induced by Dnmt1 depletion, they converted into embryonic stem (ES)-like cells. Dnmt1 depletion downregulated Dmrt1 expression, whose depletion also induced pluripotency. Functional screening of Dmrt1 target gene revealed that Dmrt1 depletion upregulates Sox2, the key molecule responsible for generating induced pluripotent stem cells. Although Sox2 transfection upregulated Oct4 and produced pluripotent cells, this conversion was inhibited by Oct1 overexpression, suggesting that the balance of Oct proteins maintains SSC identity. These results suggest that culture-induced reprogramming is caused by unstable DNA methylation, and that Dmrt1-Sox2 cascade is critical for regulating pluripotency in SSCs. Pluripotent stem-like cells were induced from GS cells by down-regulation of Dnmt/Dmrt, or up-regulation of Sox2/Oct4 in combination with p53 knock-down and their total RNA samples were subjected to microarray analysis to compare their gene expression profile with other pluripotent stem cells such as ES cells or iPS cells.