Sxl in the germline of Drosophila: A target for somatic late induction

Abstract

In Drosophila, the sex of germ cells is determined by autonomous and inductive signals. Somatic inductive signals can drive XX germ cells into oogenesis or into spermatogenesis. An autonomous signal makes XY germ cells male and unresponsive to sex determination by induction. The elements forming the X:A ratio in the soma and the genes tra, tra2, dsx, and ix that determine the sex of somatic cells have no similar role in the germline. The gene Sxl, however, is required for female differentiation of somatic and germ cells. Inductive signals that are dependent on somatic tra and dsx expression already affect the sex-specific development of germ cells of first instar larvae. At this early stage, however, germline expression of Sxl does not appear to affect the sexual characteristics of germ cells. Since inductive signals dependent on tra and dsx nevertheless influence the choice of sex-specific splicing of Sxl, it can be concluded that Sxl is a target of the inductive signal, but that its product is required late for oogenesis. Other genes must therefore control the early sexual dimorphism of larval germ cells.

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

“…Although expression of the female‐specific Sxl protein is the central female‐determination event in somatic cells, germ cell expression of Sxl is not required for establishing sexual identity in the female germ line (Salz and Erickson, ; Salz, ). In the absence of Sxl, female primordial germ cells develop normally through the end of the larval period (Steinmann‐Zwicky, ; Casper and van Doren, ; Chau et al, ). Only in the adult does Sxl function become essential, when its loss leads to a global upregulation of spermatogenesis genes and a GCT phenotype (Chau et al, ; Shapiro‐Kulnane et al, ).…”

In Drosophila, female gonadal cells repress male-specific gene expression in XX germ cells

“…Somatic sex-determining signals that act on germ cells may originate from the somatic cells of the gonads or they may be long range signals sent to the germ cells from tissue farther apart. Although the former is generally believed (Steinmann-Zwicky, 1994a), no evidence proving the existence of short range signals has been reported. Here we show that XX and XY germ cells that are not imbedded in gonads can express mgm1, while XX germ cells that are associated with female gonadal cells do not express this marker.…”

Sexual Back Talk With Evolutionary Implications: Stimulation of the Drosophila Sex-Determination Gene Sex-lethal by Its Target transformer

“…Responding to Sxl in the gonadal soma, somatic tra triggers female-specific splicing of pre-mRNA from Sxl itself in the neighboring diplo-X germ cells (Bopp et al 1993;Oliver et al 1993;Steinmann-Zwicky 1994;Waterbury et al 2000;Janzer and Steinmann-Zwicky 2001;Evans and Cline 2007). As in somatic cells, in germ cells SXL-F is necessary for female development (Schü pbach 1985), but unlike in somatic cells, it is not sufficient (Hager and Cline 1997).…”