Cell-autonomous and somatic signals control sex-specific gene expression in XY germ cells of Drosophila

When XX germ cells develop in a testis they become spermatogenic. Thus, som atic signals determine the sex of genetically female germ cells. In contras t, XY germ cells experimentally transferred to an ovary do not differentiat e oogenic cells. Because such cells show some male characteristics when ana lyzed in adults, it was assumed that XY germ cells autonomously become sper matogenic. Recently, however, evidence showing that a female soma feminizes XY germ cells was reported. The conclusion was drawn that the sex determin ation of XY germ cells is dictated by the sex of the soma. We monitored the fate of XY germ cells placed in a female environment throughout developmen t. Here we report that such germ cells respond to both cell-autonomous and somatic sex-determining signals, depending on the developmental stage. Anal yzing the expression of sex-specific molecular markers, we first detected a utonomous male-specific gene expression in XY germ cells embedded in female embryos and larvae. At later stages, however, we found that sex-specific r egulation of gene expression within XY germ cells is influenced by somatic gonadal cells. After metamorphosis, XY germ cells developing in a female so ma start expressing female-specific and male-specific markers. Transcriptio n of female-specific genes is maintained, while that of male-specific genes is later repressed. We show that in such XY germ cells, the female-specifi c gene Sex-lethal (Sxl) is activated. Within the germline, Sri expression i s required for the activation of a further female-specific gene and the rep ression of male-specific genes. We thus report for the first time the exist ence of downstream targets of the gene Sri in the germline. (C) 2001 Elsevi er Science Ireland Ltd. All rights reserved.