Antagonism between <i>germ cell-less</i> and Torso receptor regulates transcriptional quiescence underlying germline/soma distinction.

Abstract

Transcriptional quiescence, an evolutionarily conserved trait, distinguishes the embryonic primordial germ cells (PGCs) from their somatic neighbors. In <i>Drosophila melanogaster</i>, PGCs from embryos maternally compromised for <i>germ cell-less</i> (<i>gcl</i>) misexpress somatic genes, possibly resulting in PGC loss. Recent studies documented a requirement for Gcl during proteolytic degradation of the terminal patterning determinant, Torso receptor. Here we demonstrate that the somatic determinant of female fate, <i>Sex-lethal</i> (<i>Sxl</i>), is a biologically relevant transcriptional target of Gcl. Underscoring the significance of transcriptional silencing mediated by Gcl, ectopic expression of a degradation-resistant form of Torso (<i>torso^Deg</i>) can activate <i>Sxl</i> transcription in PGCs, whereas simultaneous loss of <i>torso-like</i> (<i>tsl</i>) reinstates the quiescent status of <i>gcl</i> PGCs. Intriguingly, like <i>gcl</i> mutants, embryos derived from mothers expressing <i>torso^Deg</i> in the germline display aberrant spreading of pole plasm RNAs, suggesting that mutual antagonism between Gcl and Torso ensures the controlled release of germ-plasm underlying the germline/soma distinction.