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

Tudor domain containing protein 5-like identifies a novel germline body and regulates maternal RNAs during oogenesis in Drosophila

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 plays an important role in the germline where it promotes male identity. However, Tudor domain-containing protein 5-like 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 Tudor domain-containing protein 5-like localizes to a potentially novel germline body and plays a role in posttranscriptional gene regulation. Additionally, embryos laid by Tdrd5l-mutant females exhibited reduced viability and displayed dorsal appendage defects suggesting a failure of proper dorsal-ventral patterning. As dorsal-ventral patterning is dependent on gurken (grk), we examined Gurken expression during oogenesis. We observed premature accumulation of Gurken 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, a translational activator of grk. Decreasing orb function was able to partially rescue the Tdrd5l-mutant phenotype, and so defects in Orb expression 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.

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.

Chromatin and gene expression changes during female Drosophila germline stem cell development illuminate the biology of highly potent stem cells

Highly potent animal stem cells either self renew or launch complex differentiation programs, using mechanisms that are only partly understood. Drosophila female germline stem cells (GSCs) perpetuate without change over evolutionary time and generate cystoblast daughters that develop into nurse cells and oocytes. Cystoblasts initiate differentiation by generating a transient syncytial state, the germline cyst, and by increasing pericentromeric H3K9me3 modification, actions likely to suppress transposable element activity. Relatively open GSC chromatin is further restricted by Polycomb repression of testis or somatic cell-expressed genes briefly active in early female germ cells. Subsequently, Neijre/CBP and Myc help upregulate growth and reprogram GSC metabolism by altering mitochondrial transmembrane transport, gluconeogenesis, and other processes. In all these respects GSC differentiation resembles development of the totipotent zygote. We propose that the totipotent stem cell state was shaped by the need to resist transposon activity over evolutionary timescales.

Methylation of lysine 36 on histone H3 is required to control transposon activities in somatic cells

Transposable elements constitute a substantial portion of most eukaryotic genomes and their activity can lead to developmental and neuronal defects. In the germline, transposon activity is antagonized by the PIWI-interacting RNA pathway tasked with repression of transposon transcription and degrading transcripts that have already been produced. However, most of the genes required for transposon control are not expressed outside the germline, prompting the question: what causes deleterious transposons activity in the soma and how is it managed? Here, we show that disruptions of the Histone 3 lysine 36 methylation machinery led to increased transposon transcription in Drosophila melanogaster brains and that there is division of labour for the repression of transposable elements between the different methyltransferases Set2, NSD, and Ash1. Furthermore, we show that disruption of methylation leads to somatic activation of key genes in the PIWI-interacting RNA pathway and the preferential production of RNA from dual-strand piRNA clusters.

The Drosophila Nab2 RNA binding protein inhibits m6A methylation and male-specific splicing of Sex lethal transcript in female neuronal tissue

The Drosophila polyadenosine RNA binding protein Nab2, which is orthologous to a human protein lost in a form of inherited intellectual disability, controls adult locomotion, axon projection, dendritic arborization, and memory through a largely undefined set of target RNAs. Here, we show a specific role for Nab2 in regulating splicing of ~150 exons/introns in the head transcriptome and focus on retention of a male-specific exon in the sex determination factor Sex-lethal (Sxl) that is enriched in female neurons. Previous studies have revealed that this splicing event is regulated in females by N6-methyladenosine (m6A) modification by the Mettl3 complex. At a molecular level, Nab2 associates with Sxl pre-mRNA in neurons and limits Sxl m6A methylation at specific sites. In parallel, reducing expression of the Mettl3, Mettl3 complex components, or the m6A reader Ythdc1 rescues mutant phenotypes in Nab2 flies. Overall, these data identify Nab2 as an inhibitor of m6A methylation and imply significant overlap between Nab2 and Mettl3 regulated RNAs in neuronal tissue.

Germline sex determination: How males and females tame transposons in their own ways

The piRNA pathway represses transposon activity to protect the germline genome for future generations. A new study shows how germline sex determination influences the production of different piRNAs in male and female germ cells.

Genetic control of a sex-specific piRNA program

Sexually dimorphic traits in morphologies are widely studied,1,2,3,4 but those in essential molecular pathways remain largely unexplored. Previous work showed substantial sex differences in Drosophila gonadal piRNAs,5 which guide PIWI proteins to silence selfish genetic elements, thereby safeguarding fertility.6,7,8 However, the genetic control mechanisms of piRNA sexual dimorphism remain unknown. Here, we showed that most sex differences in the piRNA program originate from the germ line rather than the gonadal somatic cells. Building on this, we dissected the contribution of sex chromosomes and cellular sexual identity toward the sex-specific germline piRNA program. We found that the presence of the Y chromosome is sufficient to recapitulate some aspects of the male piRNA program in a female cellular environment. Meanwhile, sexual identity controls the sexually divergent piRNA production from X-linked and autosomal loci, revealing a crucial input from sex determination into piRNA biogenesis. Sexual identity regulates piRNA biogenesis through Sxl, and this effect is mediated, in part, through chromatin proteins Phf7 and Kipferl. Together, our work delineated the genetic control of a sex-specific piRNA program, where sex chromosomes and sexual identity collectively sculpt an essential molecular trait.

Identification of novel candidate genes leading to sex differentiation in primordial germ cells of Drosophila

Germline sex determination and differentiation are pivotal processes in reproduction. In Drosophila, sex determination of the germline occurs in primordial germ cells (PGCs), and the sex differentiation of these cells is initiated during embryogenesis. However, the molecular mechanism initiating sex differentiation remains elusive. To address this issue, we identified sex-biased genes using RNA-sequencing data of male and female PGCs. Our research revealed 497 genes that were differentially expressed more than twofold between sexes and expressed at high or moderate levels in either male or female PGCs. Among these genes, we used microarray data of PGCs and whole embryos to select 33 genes, which are predominantly expressed in PGCs compared to the soma, as candidate genes contributing to sex differentiation. Of 497 genes, 13 genes that were differentially expressed more than fourfold between sexes were also selected as candidates. Among the 46 (33 + 13) candidates, we confirmed the sex-biased expression of 15 genes by in situ hybridization and quantitative reverse transcription-polymerase chain reaction (qPCR) analysis. Six and nine genes were predominantly expressed in male and female PGCs, respectively. These results represent a first step toward elucidating the mechanisms that initiate sex differentiation in the germline.

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

Establishing germ cell sexual identity is critical for development of male and female germline stem cells (GSCs) and production of sperm or eggs. Germ cells depend on signals from the somatic gonad to determine 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 combine to regulate germline sex determination is thus a key question. We find that JAK/STAT signaling in the GSC niche promotes male identity in germ cells, in part by activating the chromatin reader Phf7. Further, we find that JAK/STAT signaling is blocked in XX (female) germ cells through the action of the sex determination gene Sex lethal to preserve female identity. Thus, an important function of germline sexual identity is to control how GSCs respond to signals in their niche environment.

The Regulation of Germline Sex Determination in Drosophila by Sex lethal

BACKGROUND

The establishment of male or female identity (sex determination) is essential for creating the anatomical, physiological, and behavioral differences between 2 sexes of the same species (sexual dimorphism). In many organisms, including mammals and Drosophila, sex is determined by inheritance of sex chromosomes, while in other animals, sex is determined by environmental factors. Arguably the most important consequence of sex determination is the production of healthy gametes necessary for reproduction: female oocytes and male spermatids.

SUMMARY

The generation of sperm and oocytes requires cooperation between 2 different cell types within the gonad: germ cells and somatic cells. Defects in sex determination in either the somatic gonad or germline lead to disorders of sexual development and infertility. In Drosophila, the gene Sex lethal (Sxl) is the key determinant of sex in both the soma and the germline. However, how Sxl controls sex determination is much more well understood in the soma than the germline. Key Mesage: This review will focus on Sxl in the germline, how it is activated specifically in female germ cells, and how it regulates germline sex determination and sexual development.

Organ-Based Proteome and Post-Translational Modification Profiling of a Widely Cultivated Tropical Water Fish, Labeo rohita

Proteomics has enormous applications in human and animal research. However, proteomic studies in fisheries science are quite scanty particularly for economically important species. Few proteomic studies have been carried out in model fish species, but comprehensive proteomics of aquaculture species are still scarce. This study aimed to perform a comprehensive organ-based protein profiling of important tissue samples for one of the most important aquaculture species,Labeo rohita.Deep proteomic profiling of 17 histologically normal tissues, blood plasma, and embryo provided mass-spectrometric evidence for 8498 proteins at 1% false discovery rate that make up about 26% of the total annotated protein-coding sequences in Rohu. Tissue-wise expression analysis was performed, and the presence of several biologically important proteins was also verified using a targeted proteomic approach. We identified the global post-translational modifications (PTMs) in terms of acetylation (N-terminus and lysine), methylation (N-terminus, lysine, and arginine), and phosphorylation (serine, threonine, and tyrosine) to present a comprehensive proteome resource. An interactive web-based portal has been developed for an overall landscape of protein expression across the studied tissues of Labeo rohita (www.fishprot.org). This draft proteome map of Labeo rohita would advance basic and applied research in aquaculture to meet the most critical challenge of providing food and nutritional security to an increasing world population.

Germline masculinization by Phf7 in D. melanogaster requires its evolutionarily novel C-terminus and the HP1-family protein HP1D3csd

Germ cells in Drosophila melanogaster need intrinsic factors along with somatic signals to activate proper sexual programs. A key factor for male germline sex determination is PHD finger protein 7 (Phf7), a histone reader expressed in the male germline that can trigger sex reversal in female germ cells and is also important for efficient spermatogenesis. Here we find that the evolutionarily novel C-terminus in Phf7 is necessary to turn on the complete male program in the early germline of D. melanogaster, suggesting that this domain may have been uniquely acquired to regulate sexual differentiation. We further looked for genes regulated by Phf7 related to sex determination in the embryonic germline by transcriptome profiling of FACS-purified embryonic gonads. One of the genes positively-regulated by Phf7 in the embryonic germline was an HP1family member, Heterochromatin Protein 1D3 chromoshadow domain (HP1D3csd). We find that this gene is needed for Phf7 to induce male-like development in the female germline, indicating that HP1D3csd is an important factor acting downstream of Phf7 to regulate germline masculinization.

Absence of X-chromosome dosage compensation in the primordial germ cells of Drosophila embryos

Dosage compensation is a mechanism that equalizes sex chromosome gene expression between the sexes. In Drosophila, individuals with two X chromosomes (XX) become female, whereas males have one X chromosome (XY). In males, dosage compensation of the X chromosome in the soma is achieved by five proteins and two non-coding RNAs, which assemble into the male-specific lethal (MSL) complex to upregulate X-linked genes twofold. By contrast, it remains unclear whether dosage compensation occurs in the germline. To address this issue, we performed transcriptome analysis of male and female primordial germ cells (PGCs). We found that the expression levels of X-linked genes were approximately twofold higher in female PGCs than in male PGCs. Acetylation of lysine residue 16 on histone H4 (H4K16ac), which is catalyzed by the MSL complex, was undetectable in these cells. In male PGCs, hyperactivation of X-linked genes and H4K16ac were induced by overexpression of the essential components of the MSL complex, which were expressed at very low levels in PGCs. Together, these findings indicate that failure of MSL complex formation results in the absence of X-chromosome dosage compensation in male PGCs.

Sex Differences in Intestinal Carbohydrate Metabolism Promote Food Intake and Sperm Maturation

Physiology and metabolism are often sexually dimorphic, but the underlying mechanisms remain incompletely understood. Here, we use the intestine of Drosophila melanogaster to investigate how gut-derived signals contribute to sex differences in whole-body physiology. We find that carbohydrate handling is male-biased in a specific portion of the intestine. In contrast to known sexual dimorphisms in invertebrates, the sex differences in intestinal carbohydrate metabolism are extrinsically controlled by the adjacent male gonad, which activates JAK-STAT signaling in enterocytes within this intestinal portion. Sex reversal experiments establish roles for this male-biased intestinal metabolic state in controlling food intake and sperm production through gut-derived citrate. Our work uncovers a male gonad-gut axis coupling diet and sperm production, revealing that metabolic communication across organs is physiologically important. The instructive role of citrate in inter-organ communication might be significant in more biological contexts than previously recognized.

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Intestinal carbohydrate metabolism is male-biased and region-specific

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Testes masculinize gut sugar handling by promoting enterocyte JAK-STAT signaling

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The male intestine secretes citrate to the adjacent testes

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Gut-derived citrate promotes food intake and sperm maturation

Post-transcriptional gene regulation regulates germline stem cell to oocyte transition during Drosophila oogenesis

During oogenesis, several developmental processes must be traversed to ensure effective completion of gametogenesis including, stem cell maintenance and asymmetric division, differentiation, mitosis and meiosis, and production of maternally contributed mRNAs, making the germline a salient model for understanding how cell fate transitions are mediated. Due to silencing of the genome during meiotic divisions, there is little instructive transcription, barring a few examples, to mediate these critical transitions. In Drosophila, several layers of post-transcriptional regulation ensure that the mRNAs required for these processes are expressed in a timely manner and as needed during germline differentiation. These layers of regulation include alternative splicing, RNA modification, ribosome production, and translational repression. Many of the molecules and pathways involved in these regulatory activities are conserved from Drosophila to humans making the Drosophila germline an elegant model for studying the role of post-transcriptional regulation during stem cell differentiation and meiosis.