Germline cysts require Ecdysone receptor for proper timing of encapsulation in the Drosophila ovary

Oocytes are packaged into ovarian follicles, each containing a maturing germ cell surrounded by a layer of somatic cells. This conserved arrangement is essential for proper oocyte development and reproductive success. Continuous coordination and bi-directional signaling from somatic cells to germ cells are necessary for proper oocyte packaging. In Drosophila, although germ cell packaging has been presumed to be controlled by somatic follicle cells enveloping passive germ cells, recent studies suggest that germ cells themselves produce motor forces that drive somatic encapsulation. Here, in support of this hypothesis, we present data suggesting that cyst encapsulation requires Ecdysone receptor (EcR), a steroid hormone receptor known to control multiple aspects of oogenesis. Using tools to deplete EcR or block EcR signaling specifically in the germline, we show that germline-autonomous EcR is necessary for the timing of cyst encapsulation. When EcR signaling is inactivated, germ cell encapsulation is slowed, resulting in abnormal oocyte positioning and decreased fecundity. EcR facilitates germ cell cyst encapsulation by promoting proliferation and intercalation of overlying somatic cells. We conclude that EcR likely promotes cyst packaging by specifically inducing EGFR signaling in posterior escort and follicle cells. Overall, these data demonstrate that EcR is necessary in the germline to promote timely ovarian follicle assembly and development.