Phenotypic and molecular characterization of vreteno, a novel gene required for germ line differentiation in Drosophila

In stem cells, self-renewal and differentiation are two processes that must be carefully balanced. We have characterized vreteno (vret), a gene recovered from a maternal effect screen that is required for germ line differentiation in both males and females, in addition to having a sex-specific function in oocyte patterning. Both males and females transheterozygous for strong alleles of vret are sterile. vret mutant ovaries have stem cell tumors and defective egg chambers, and vret testes display an increase in germ line stem cells, gonialblasts and early spermatogonial cysts. vret is required at distinct time points in different tissues in the ovary: vret is required early in oogenesis in the soma for germ line stem cell differentiation, and later in the germ line for oocyte patterning.{09}In addition, defects in the physical interaction between somatic and germ line tissues are also present throughout the ovary in strong, but not in weak, vret alleles.; We have identified a novel tudor domain-containing gene as the locus for vret. vret is a gonad-specific gene expressed in the germ line of both males and females. Clonal analysis, pole cell transplantation, and misexpression studies in the ovary suggest that vret is required non-autonomously in the somatic niche, most likely the inner sheath cells, for germ line stem cell differentiation. In contrast to the ovary, vret is required autonomously in the germ line for differentiation of spermatogonial cysts.; vret stem cell tumors in the ovary have an expansion of dpp signaling in germ line stem cells outside of the niche, suggesting that vret promotes differentiation by repressing the instructive stem cell maintenance signal dpp. vret represses dpp signaling upstream of bag of marbles, a gene necessary and sufficient for germ line stem cell differentiation. In addition, epistasis experiments indicate that vret acts upstream or parallel to the stem cell maintenance signals piwi and pumilio. Together, our results suggest that the novel tudor domain containing gene vret may function in restricting or refining germ line stem cell-maintenance signals from the somatic niche.