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

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.

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.

Male-biased protein expression in primordial germ cells, identified through a comparative study of UAS vectors in Drosophila

In Drosophila, three types of UAS vectors (UASt, UASp, and UASz) are currently available for use with the Gal4-UAS system. They have been used successfully in somatic cells and germline cells from ovaries. However, it remains unclear whether they are functional in the germline cells of embryos, larvae, and adult testes. In this study, we found that all three types of UAS vectors were functional in the germline cells of embryos and larvae and that the UASt and UASz vectors were active in the germline of the distal tip region in adult testes. Moreover, we observed that protein expression from the UAS vectors was male-biased in germline cells of late embryos, whereas their respective mRNA expression levels were not. Furthermore, O-propargyl-puromycin (OPP) staining revealed that protein synthesis was male-biased in these germline cells. In addition, GO terms related to translation and ribosomal maturation were significantly enriched in the male germline. These observations show that translational activity is higher in male than in female germline cells. Therefore, we propose that male-biased protein synthesis may be responsible for the sex differences observed in the early germline.