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

Abstract

In Drosophila, the sex of XX germ cells is determined by somatic signals. Whether sex-specific genes, however, are activated or repressed by somatic signals is not known. We have used mgm1, a germline-marker which is specifically expressed in male germ cells to analyze sex-specific gene expression of embryonic germ cells. We found that XX and XY germ cells that do not contact gonadal tissue can express mgm1. In contrast, XX germ cells that were associated with female somatic gonadal cells never expressed mgm1. Our results suggest that XX germ cells express male-specific genes, unless these genes are repressed by feminizing short range signals produced by the somatic cells of the prospective ovary.

The establishment of sexual identity in theDrosophilagermline

“…3B). This repression has also been observed with mgm-1 (Heller and Steinmann-Zwicky, 1998). In addition, XY germ cells exhibit some female-specific otu expression when in contact with a female soma (UAS-tra, Fig.…”

“…We used the newly identified sexspecific molecular markers to determine how these two components contribute to the establishment of germline sexual identity in the embryo. Previous studies have shown that mgm-1 is expressed in both XX and XY germ cells that are not in contact with the somatic gonad, suggesting that male identity in the germline is the 'default' in the absence of the somatic gonad (Heller and Steinmann-Zwicky, 1998).…”

“…This indicates that the female soma is able to repress male-specific gene expression (Heller and Steinmann-Zwicky, 1998). To examine this further, we analyzed gene expression in XY germ cells in contact with a female soma.…”

“…Just after gonad coalescence (stage 15), male germ cells express male germline marker-1 (mgm-1), which appears to be an enhancer trap in the escargot locus (Staab et al, 1996;Streit et al, 2002). XX germ cells can express this male marker when present in a male soma (Janzer and Steinmann-Zwicky, 2001;Staab et al, 1996) or when not in contact with the somatic gonad (Heller and Steinmann-Zwicky, 1998), indicating that the female gonad represses mgm-1 expression in XX germ cells. However, mgm-1 expression is still observed in XY germ cells present in a female soma, at least initially, indicating that the female soma is unable to repress this aspect of male identity (Janzer and Steinmann-Zwicky, 2001).…”

The control of sexual identity in theDrosophilagermline

“…XY germ cells initiate mgm1 expression even in a female somatic environment, indicating that it is regulated by the germ cell genotype (Heller and Steinmann-Zwicky, 1998;Janzer and Steinmann-Zwicky, 2001). mgm1 expression is also regulated by the soma, as XY germ cells cannot maintain mgm1 expression in a female soma (Janzer and Steinmann-Zwicky, 2001).…”