Chinmo is sufficient to induce male fate in somatic cells of the adult Drosophila ovary

The pioneer factor Zelda induces male-to-female somatic sex reversal in adult tissues

Somatic sex identity must be maintained throughout adulthood for tissue function. Adult somatic stem cells in the Drosophila testis (i.e., CySCs) lacking the transcription factor Chinmo are reprogrammed to their ovarian counterparts by induction of female-specific Tra F , but this is not mechanistically understood. Pioneer factors play central roles in direct reprogramming, and many upregulated genes in chinmo -/- CySCs contain binding sites for the pioneer factor Zelda (Zld). microRNAs repress zld mRNA in wild type CySCs, but they are downregulated after Chinmo loss, allowing for zld mRNA translation. Zld depletion from chinmo -/- CySCs suppresses feminization, and ectopic Zld induces Tra F and feminizes wild-type CySCs. qkr58E-2 and ecdysone receptor ( EcR ), direct Zld targets in the embryo, are female-biased in adult gonads and upregulated in chinmo -/- CySCs. The RNA-binding protein Qkr58E-2 produces Tra F , while EcR promotes female-biased gene expression. Ectopic Zld feminizes adult male adipose tissue, demonstrating that Zld can instruct female and override male identity in adult XY tissues.

Highlights

zld mRNA is repressed by microRNAs in XY somatic gonadal cells Zld is upregulated in and required for sex reversal of XY chinmo -/- cells Zld induces Qkr58E-2 and EcR, which cause Tra F and female-biased transcription Zld feminizes XY adipose cells by inducing Tra F and downregulating Chinmo.

Identification of sex-biased and gonadal developmental miRNAs during critical windows of early gonadal differentiation in the Chinese giant salamander (Andrias davidianus)

The Chinese giant salamander (CGS), Andrias davidianus, the largest living amphibian, is of significant conservation importance for its wild populations and serves as a valuable economic species in aquaculture. Given that male CGS are larger than female, understanding the mechanisms behind gonadal differentiation and development is critical for optimizing production in aquaculture. This study conducted small RNA-seq on male and female gonads during two key differentiation windows in CGS. PCA analysis revealed distinct clustering within groups and clear differentiation between groups. A total of 374 miRNAs were identified, including 162 known and 212 novel miRNAs. Differential expression and enrichment analysis across the two time points identified nine sex-biased miRNAs involved in CGS gonadal differentiation, including let-7b-3p, miR-3529-3p, miR-34c-5p, miR-10-5p, miR-7-5p, and four novel miRNAs, and network of these nine sex-biased miRNAs with their target genes were constructed. Furthermore, our findings suggest that male and female gonadal development processes are likely regulated by distinct miRNAs. This study provides a comprehensive analysis of sex-biased and gonadal development related miRNAs in CGS, offering a theoretical foundation for enhancing CGS aquaculture productivity through targeted sex ratio management.

Soma-germline communication drives sex maintenance in the Drosophila testis

In adult gonads, disruption of somatic sexual identity leads to defective gametogenesis and infertility. However, the underlying mechanisms by which somatic signals regulate germline cells to achieve proper gametogenesis remain unclear. In our previous study, we introduced the chinmoSex Transformation (chinmoST ) mutant Drosophila testis phenotype as a valuable model for investigating the mechanisms underlying sex maintenance. In chinmoST testes, depletion of the Janus Kinase-Signal Transducer and Activator of Transcription downstream effector Chinmo from somatic cyst stem cells (CySCs) feminizes somatic cyst cells and arrests germline differentiation. Here, we use single-cell RNA sequencing to uncover chinmoST -specific cell populations and their transcriptomic changes during sex transformation. Comparative analysis of intercellular communication networks between wild-type and chinmoST testes revealed disruptions in several soma-germline signaling pathways in chinmoST testes. Notably, the insulin signaling pathway exhibited significant enhancement in germline stem cells (GSCs). Chinmo cleavage under targets and tagmentation (CUT&Tag) assay revealed that Chinmo directly regulates two male sex determination factors, doublesex (dsx) and fruitless (fru), as well as Ecdysone-inducible gene L2 (ImpL2), a negative regulator of the insulin signaling pathway. Further genetic manipulations confirmed that the impaired gametogenesis observed in chinmoST testes was partly contributed by dysregulation of the insulin signaling pathway. In summary, our study demonstrates that somatic sex maintenance promotes normal spermatogenesis through Chinmo-mediated conserved sex determination and the insulin signaling pathway. Our work offers new insights into the complex mechanisms of somatic stem cell sex maintenance and soma-germline communication at the single-cell level. Additionally, our discoveries highlight the potential significance of stem cell sex instability as a novel mechanism contributing to testicular tumorigenesis.

Differentiating Drosophila female germ cells initiate Polycomb silencing by regulating PRC2-interacting proteins

Polycomb silencing represses gene expression and provides a molecular memory of chromatin state that is essential for animal development. We show that Drosophila female germline stem cells (GSCs) provide a powerful system for studying Polycomb silencing. GSCs have a non-canonical distribution of PRC2 activity and lack silenced chromatin like embryonic progenitors. As GSC daughters differentiate into nurse cells and oocytes, nurse cells, like embryonic somatic cells, silence genes in traditional Polycomb domains and in generally inactive chromatin. Developmentally controlled expression of two Polycomb repressive complex 2 (PRC2)-interacting proteins, Pcl and Scm, initiate silencing during differentiation. In GSCs, abundant Pcl inhibits PRC2-dependent silencing globally, while in nurse cells Pcl declines and newly induced Scm concentrates PRC2 activity on traditional Polycomb domains. Our results suggest that PRC2-dependent silencing is developmentally regulated by accessory proteins that either increase the concentration of PRC2 at target sites or inhibit the rate that PRC2 samples chromatin.

Signal transduction in the early Drosophila follicle stem cell lineage

The follicle stem cell (FSC) lineage in the Drosophila ovary is a highly informative model of in vivo epithelial stem cell biology. Studies over the past 30 years have identified roles for every major signaling pathway in the early FSC lineage. These pathways regulate a wide variety of cell behaviors, including self-renewal, proliferation, survival and differentiation. Studies of cell signaling in the follicle epithelium have provided new insights into how these cell behaviors are coordinated within an epithelial stem cell lineage and how signaling pathways interact with each other in the native, in vivo context of a living tissue. Here, we review these studies, with a particular focus on how these pathways specify differences between the FSCs and their daughter cells. We also describe common themes that have emerged from these studies, and highlight new research directions that have been made possible by the detailed understanding of the follicle epithelium.

The H3K9 methyltransferase SETDB1 maintains female identity in Drosophila germ cells

The preservation of germ cell sexual identity is essential for gametogenesis. Here we show that H3K9me3-mediated gene silencing is integral to female fate maintenance in Drosophila germ cells. Germ cell specific loss of the H3K9me3 pathway members, the H3K9 methyltransferase SETDB1, WDE, and HP1a, leads to ectopic expression of genes, many of which are normally expressed in testis. SETDB1 controls the accumulation of H3K9me3 over a subset of these genes without spreading into neighboring loci. At phf7, a regulator of male germ cell sexual fate, the H3K9me3 peak falls over the silenced testis-specific transcription start site. Furthermore, H3K9me3 recruitment to phf7 and repression of testis-specific transcription is dependent on the female sex determination gene Sxl. Thus, female identity is secured by an H3K9me3 epigenetic pathway in which Sxl is the upstream female-specific regulator, SETDB1 is the required chromatin writer, and phf7 is one of the critical SETDB1 target genes.

Epigenetic regulation is critical for the maintenance of germ cell identity. Here the authors show that H3K9me3-mediated gene silencing is critical for repression of testis-specific transcription in Drosophila female germ cells, indicating H3K9me3 maintains female germ cell sexual identity.

Chinmo prevents transformer alternative splicing to maintain male sex identity

Reproduction in sexually dimorphic animals relies on successful gamete production, executed by the germline and aided by somatic support cells. Somatic sex identity in Drosophila is instructed by sex-specific isoforms of the DMRT1 ortholog Doublesex (Dsx). Female-specific expression of Sex-lethal (Sxl) causes alternative splicing of transformer (tra) to the female isoform traF. In turn, TraF alternatively splices dsx to the female isoform dsxF. Loss of the transcriptional repressor Chinmo in male somatic stem cells (CySCs) of the testis causes them to "feminize", resembling female somatic stem cells in the ovary. This somatic sex transformation causes a collapse of germline differentiation and male infertility. We demonstrate this feminization occurs by transcriptional and post-transcriptional regulation of traF. We find that chinmo-deficient CySCs upregulate tra mRNA as well as transcripts encoding tra-splice factors Virilizer (Vir) and Female lethal (2)d (Fl(2)d). traF splicing in chinmo-deficient CySCs leads to the production of DsxF at the expense of the male isoform DsxM, and both TraF and DsxF are required for CySC sex transformation. Surprisingly, CySC feminization upon loss of chinmo does not require Sxl but does require Vir and Fl(2)d. Consistent with this, we show that both Vir and Fl(2)d are required for tra alternative splicing in the female somatic gonad. Our work reveals the need for transcriptional regulation of tra in adult male stem cells and highlights a previously unobserved Sxl-independent mechanism of traF production in vivo. In sum, transcriptional control of the sex determination hierarchy by Chinmo is critical for sex maintenance in sexually dimorphic tissues and is vital in the preservation of fertility.

Germ cell tumors: Insights from the Drosophila ovary and the mouse testis

Ovarian and testicular germ cell tumors of young adults are thought to arise from defects in germ cell development, but the molecular mechanisms underlying malignant transformation are poorly understood. In this review, we focus on the biology of germ cell tumor formation in the Drosophila ovary and the mouse testis, for which evidence supports common underlying mechanisms, such as blocking initiation into the differentiation pathway, impaired lineage progression, and sexual identity instability. We then discuss how these concepts inform our understanding of the disease in humans. Mol. Reprod. Dev. 84: 200-211, 2017. © 2017 Wiley Periodicals, Inc.