Drosophila melanogasterMale Somatic Cells Feminized Solely by TraF Can Collaborate With Female Germ Cells to Make Functional Eggs

Abstract

Female differentiation of Drosophila germ cells is induced by cell-nonautonomous signals generated in the gonadal soma that work with germ-cell-autonomous signals determined by germ-cell X chromosome dose. Generation of the nonautonomous feminizing signals was known to involve female-specific protein encoded by the master sex-determination gene Sex-lethal (Sxl) acting on its switch-gene target transformer (tra) to produce TraF protein. However, it was not known whether Sxl's action on tra alone would suffice to trigger a fully feminizing nonautonomous signal. We developed a constitutively feminizing tra transgene that allowed us to answer this question. In gynanders (XX//XO mosaics) feminized by this TraF transgene, functionally Sxl− haplo-X (chromosomally male) somatic cells collaborated successfully with diplo-X (chromosomally female) germ cells to make functional eggs. The fertility of such gynanders shows not only that TraF is sufficient to elicit a fully feminizing nonautonomous signal, but also that haplo-X somatic cells can execute all other somatic functions required for oogenesis, despite the fact that their genome is not expected to be dosage compensated for such diplo-X-specific functions. The unexpected observation that some TraF-feminized gynanders failed to lay their eggs showed there to be diplo-X cells outside the gonad for which TraF-feminized haplo-X cells cannot substitute.

Phf7 Controls Male Sex Determination in the Drosophila Germline

“…By in situ hybridization, such XX germline was found to express Phf7 at levels similar to control XY germline (Figure 1G). Conversely, we tested if XY germ cells surrounded by female soma can still express Phf7 by feminizing the somatic gonad of XY embryos through general expression of traF ( U2AF-traF , Evans and Cline, 2007). We observed that Phf7 expression in XY germ cells is repressed when in contact with female soma, but the expression level is still higher than XX germ cells in contact with female soma (Figure 1G), suggesting that XY germ cells are able to upregulate Phf7 expression intrinsically.…”

Drosophila switch gene Sex-lethal can bypass its switch-gene target transformer to regulate aspects of female behavior

“…Females carrying the transgene but lacking endogenous tra + gene function made eggs and mated but were sterile, at least in part because they failed to lay their eggs. Our Tra-F transgene driven by a U2af50 promoter overcame this limitation (16). U2af50 is a ubiquitously expressed RNA-splicing housekeeping gene.…”

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

“…As mentioned in the results, we cannot exclude a rather complex cellautonomous alternative model for Sxl f9 feedback loop engagement, but we favor the cell-nonautonomous alternative since female somatic cells in the gonad have already been shown to trigger female expression of Sxl in neighboring germ cells that have been ''sensitized'' by having two X chromosomes rather than one (SteinmannZwicky et al 1989). Indeed, Evans and Cline (2007) showed that forced expression of TRA-F even in chromosomally male gonadal soma with no SXL-F is sufficient to stimulate SXL-F expression in neighboring diplo-X germ cells to a level adequate for producing fully functional eggs. Hence, our cell-nonautonomous model has these somatic cells simply doing to each other what they are already known to do to germ cells.…”

“…Markers, balancers, and transgenes are described at http:/ /flybase.bio.indiana.edu/ except as follows: Df(tud) and tud B45-6 were a gift from R. Lehmann; P{U2af50-traF w 1mW.hs }2B allows one to maintain tra À homozygous stocks (Evans and Cline 2007). The Binsinscy, y w sn x2 B let P{w…”

“…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).…”