Biology subjects

Van Doren, M.

Publications and source records attributed to Van Doren, M..

7 recordsLinked to original sources

bioRxiv2023

Steroid signaling controls sex-specific development in an invertebrate

In vertebrate sexual development, two important steroid hormones, testosterone and estrogen, regulate the sex-specific development of many tissues. In contrast, invertebrates utilize a single steroid hormone, ecdysone, to regulate developmental timing in both sexes. However, here we show that in Drosophila melanogaster, sex-specific ecdysone (E) signaling controls important aspects of gonad sexual dimorphism. Rather than being regulated at the level of hormone production, hormone activity is regulated cell-autonomously through sex-specific hormone reception. Ecdysone receptor (EcR) expression is restricted to the developing ovary and is repressed in the testis at a time when ecdysone initiates ovary morphogenesis. Interestingly, EcR expression is regulated downstream of the sex determination factor Doublesex (Dsx), the founding member of the Dsx/Mab3 Related Transcription Factor (DMRT) family that regulates gonad development in all animals. E signaling is required for normal ovary development1,2, and ectopic activation of E signaling in the testis antagonized stem cell niche identity and feminized somatic support cells, which were transformed into follicle-like cells. This work demonstrates that invertebrates can also use steroid hormone signaling to control sex-specific development. Further, it may help explain recent work showing that vertebrate sexual development is surprisingly cell-autonomous. For example, chickens utilize testosterone and estrogen to control sex-specific development, but when they have a mixture of cells with male and female genotypes, the male cells develop as male and the female cells develop as female despite exposure to the same circulating hormones3. Sex-specific regulation of steroid hormone signaling may well underly such cell-autonomous sexual fate choices in vertebrates as it does in Drosophila.

developmental biology↗

bioRxiv2022

Tudor domain containing protein 5-like (Tdrd5l) identifies a novel germline granule that regulates maternal RNAs

Tudor domain-containing proteins are conserved across the animal kingdom for their function in germline development and fertility. Previously, we demonstrated that Tudor domain-containing protein 5-like (Tdrd5l) plays an important role in the germline where it promotes male identity. However, Tdrd5l is also expressed in both the ovary and testis during later stages of germline development, suggesting that it plays a role in germline differentiation in both sexes. We found that Tdrd5l localizes to a potentially novel germline body and plays a role in post-transcriptional gene regulation. RNA sequencing of Tdrd5l-mutant ovaries compared to wild-type showed that differentially expressed genes were enriched for maternally deposited RNAs. Additionally, embryos laid by Tdrd5l-mutant females exhibited reduced viability and displayed dorsal appendage defects suggesting a failure of proper dorsal-ventral (D/V) patterning. As D/V patterning is dependent on gurken (grk), we examined Grk expression during oogenesis. We observed premature accumulation of Grk protein in nurse cells indicating that translation is no longer properly repressed during mRNA transport to the oocyte. We also observed increased nurse cell accumulation of the cytoplasmic polyadenylation element binding protein Oo18 RNA-Binding Protein (Orb or CPEB), a translational activator of Grk. Decreasing orb function was able to partially rescue the Tdrd5l-mutant phenotype, and so defects in Orb are likely a primary cause of the defects in Tdrd5l mutants. Our data indicate that Tdrd5l is important for translational repression of maternal mRNAs such as orb, and possibly others, following their synthesis in the nurse cells and during their transport to the oocyte.

developmental biology↗

bioRxiv2021

Germline Sex Determination regulates sex-specific signaling between germline stem cells and their niche

The establishment of sexual identity in germ cells is critical for the development of male and female germline stem cells (GSCs) and production of sperm vs. eggs. Thus, this process is essential for sexual reproduction and human fertility. Germ cells depend on signals from the somatic gonad to determine their sex, but in organisms such as flies, mice and humans, the sex chromosome genotype of the germ cells is also important for germline sexual development. How somatic signals and germ cell-intrinsic cues act together to regulate germline sex determination is a key question about which little is known. We have found that JAK/STAT signaling in the GSC niche promotes male identity in germ cells and GSCs, in part by activating expression of the epigenetic reader Phf7. We have also found that JAK/STAT signaling is blocked in XX (female) germ cells through the intrinsic action of the sex determination gene Sex lethal, which preserves female identity. Thus, an important function of germline sexual identity is to control how GSCs respond to signals in their niche environment.

developmental biology↗

bioRxiv2019

sisterless A is required for the activation of Sex lethal in the germline

Both somatic cells and germ cells must establish their correct sexual identity for proper gametogenesis. In Drosophila, sex determination in somatic cells is controlled by the switch gene Sex lethal (Sxl), which is activated in females by the presence of two X chromosomes. Though germline sex determination is much less well understood, Sxl is also essential for the female identity in germ cells. Loss of Sxl function in the germline results in ovarian germline tumors, a characteristic of male germ cells developing in a female soma. Further, Sxl expression is sufficient for XY (male) germ cells to produce eggs when transplanted into XX (female) somatic gonads. As in the soma, the presence of two X chromosomes activates Sxl in the germline, but the mechanism for "counting" X chromosomes in the germline is thought to be different from the soma. Here we have explored this mechanism at both cis- and trans- levels. Our data support the model that the Sxl "establishment" promoter (SxlPE) is activated in a female-specific manner in the germline, as in the soma, but that the timing of SxlPE activation, and the DNA elements that regulate SxlPE, are different in the germline. Nevertheless, we find that the X chromosome gene sisterless A (sisA), which helps activate Sxl in the soma, is also essential for Sxl activation in the germline. Loss of sisA leads causes of Sxl expression in the germline, and to ovarian tumors and germline loss. These defects can be rescued by Sxl expression, demonstrating that sisA lies upstream of Sxl in germline sex determination. We conclude that sisA acts as an X chromosome counting element in both the soma and the germline, but that additional factors regulating female-specific expression of Sxl in the germline remain to be discovered. AUTHOR SUMMARYThe production of sperm and eggs requires proper sexual identity to be established in both somatic cells and the germ cells, which ultimately produce the gametes. While somatic sex determination has been well studied in a number of organisms, how germ cells establish their sexual identity is much less well understood. In Drosophila, the RNA binding protein Sex lethal (Sxl) is essential for female sexual identity in both the soma and the germline, but its regulation in the germline is thought to be different than in the soma. Here we explore how Sxl is activated in the germline. We find that the germline uses a different set of DNA elements to control activation of the key sex-specific Sxl promoter. Nonetheless, one of the activators of Sxl in the soma, the transcription factor Sisterless A (SisA), also acts to activate Sxl in the germline. Our data indicate that, while SisA acts as a common activator in both the soma and germline, additional, germline-specific Sxl activators remain to be discovered.

developmental biology↗

bioRxiv2018

fruitless functions downstream of doublesex to promote sexual dimorphism of the gonad stem cell niche

Backgrounddoublesex (dsx) and fruitless (fru) are the two downstream transcription factors that actuate Drosophila sex determination. While dsx assists fru to regulate sex-specific behavior, whether fru collaborates with dsx in regulating other aspects of sexual dimorphism remains unknown. One important aspect of sexual dimorphism is found in the gonad stem cell (GSC) niches, where male and female GSCs are regulated to create large numbers of sperm and eggs.\n\nResultsHere we report that Fru is expressed male-specifically in the GSC niche and plays important roles in the development and maintenance of these cells. Unlike previously studied regulation of sex-specific Fru expression, which is regulated by alternative splicing by Transformer (Tra), we show that male-specific expression of fru is regulated downstream of dsx, and is independent of Tra. Regulation of fru by dsx also occurs in the nervous system. fru genetically interacts with dsx to support maintenance of the hub throughout development. Ectopic expression of fru inhibited female niche formation and partially masculinized the ovary. fru is also required autonomously for cyst stem cell maintenance and cyst cell survival. Finally, we identified a conserved Dsx binding site upstream of fru promoter P4 that regulates fru expression in the hub, indicating that fru is likely a direct target for transcriptional regulation by Dsx.\n\nConclusionsThese findings demonstrate that fru acts outside the nervous system to influence sexual dimorphism and reveal a new mechanism for regulating sex-specific expression of fru that is regulated at the transcriptional level by Dsx, rather than by alternative splicing by Tra.

developmental biology↗

bioRxiv2018

tudor-domain containing protein 5-prime promotes male sexual identity in the Drosophila germline and is repressed in females by Sex lethal

For sexually reproducing organisms, production of male or female gametes depends on specifying the correct sexual identity in the germline. In D. melanogaster, Sex lethal (Sxl) is the key gene that controls sex determination in both the soma and the germline, but how it does so in the germline is unknown, other than that it is different than in the soma. We conducted an RNA expression profiling experiment to identify direct and indirect germline targets of Sxl specifically in the undifferentiated germline. We find that, in these cells, Sxl loss does not lead to a global masculinization observed at the whole-genome level. In contrast, Sxl appears to affect a discrete set of genes required in the male germline, such as Phf7. We also identify tudor domain containing protein 5-prime (tdrd5p) as a target for Sxl regulation that is important for male germline identity. tdrd5p is repressed by Sxl in female germ cells, but is highly expressed in male germ cells where it promotes proper male fertility and germline differentiation. Additionally, Tdrd5p localizes to cytoplasmic granules with some characteristics of RNA Processing (P-) Bodies, suggesting that it promotes male identity in the germline by regulating post-transcriptional gene expression.\n\nAuthor summaryLike humans, all sexually reproducing organisms require gametes to reproduce. Gametes are made by specialized cells called germ cells, which must have the correct sexual identity information to properly make sperm or eggs. In fruit flies, germ cell sexual identity is controlled by the RNA-binding protein Sxl, which is expressed only in females. To better understand how Sxl promotes female identity, we conducted an RNA expression profiling experiment to identify genes whose expression changes in response to the loss of Sxl from germ cells. Here, we identify tudor domain containing protein 5-prime (tdrd5p), which is expressed 17-fold higher in ovaries lacking Sxl compared to control ovaries. Additionally, tdrd5p plays an important role in males as male flies that are mutant for this gene cannot make sperm properly and thus are less fertile. Moreover, we find that tdrd5p promotes male identity in the germline, as several experiments show that it can shift the germ cell developmental program from female to male. This study tells us that Sxl promotes female identity in germ cells by repressing genes, like tdrd5p, that promote male identity. Future studies into the function of tdrd5p will provide mechanistic insight into how this gene promotes male identity.

developmental biology↗

bioRxiv2018

The creation of sexual dimorphism in Drosophila gonad stem cell niches

Sex-specific development of the gonads is a key aspect of sexual dimorphism that is regulated by Doublesex/Mab3 Related Transcription Factors (DMRTs) in diverse animals species. We find that in mutants for Drosophila dsx, important components of the male and female gonad stem cell niches (hubs and terminal filaments/cap cells, respectively) still form. Initially, gonads in all dsx mutants (both XX and XY) initiate the male program of development, but later half of these gonads switch to form female stem cell niche structures. One individual can have both male-type and female-type gonad niches, however male and female niches are usually not observed in the same gonad, indicating that cells make a \"group decision\" about which program to follow. We conclude that dsx does not act in an instructive manner to regulate male vs. female niche formation, as these structures form in the absence of dsx function. Instead, dsx acts to \"tip the balance\" between the male or female programs, which are then executed independent of dsx. We show that bric a brac acts downstream of dsx to control the male vs. female niche decision. These results indicate that, in both flies and mammals, the sexual fate of the somatic gonad is remarkably plastic and is controlled by a combination of autonomous and non-autonomous cues.

developmental biology↗