Ecdysone receptor autonomously controls germ cell differentiation in the Drosophila ovary

The steroid hormone ecdysone controls Drosophila ovarian germline stem cell (GSC) maintenance and germ cell differentiation. Prior studies demonstrated that ecdysone regulates germ cell differentiation non-autonomously via the nuclear receptor Ecdysone receptor (EcR) in ovarian somatic cells. Although EcR is also expressed in germ cells, potential direct roles for EcR in the germline independent of the soma have not been examined. Here, we demonstrate that EcR functions autonomously in GSCs and cystoblasts to control germline differentiation. While depletion of EcR from GSCs mildly reduces their maintenance, overexpression of EcR specifically in GSCs and cystoblasts impedes germ cell differentiation, phenotypically resembling loss of function of bag of marbles (bam) and bone morphogenetic protein signaling constitutive activation. We propose that EcR functions as a transcriptional repressor in GSCs and cystoblasts to suppress differentiation but becomes derepressed as the ecdysone titer increases and expression of the co-repressor Smrter decreases in dividing germ cell cysts, providing temporal control over germline differentiation. These data support the model that germ cells integrate signals from multiple cell sources that spatially and temporally control their differentiation in response to local and physiological cues.