Ecdysone regulates phagocytic cell fate of epithelial cells in developing <i>Drosophila</i> eggs

Acquisition of nonprofessional phagocytic cell fate plays an important role in sculpting functional metazoan organs and maintaining overall tissue homeostasis. Though physiologically highly relevant, how the normal epithelial cells acquire phagocytic fate is still mostly unclear. We have employed the Drosophila ovary model to demonstrate that the classical ecdysone signaling in the somatic epithelial follicle cells (AFCs) aids the removal of germline nurse cells (NCs) in late oogenesis. Our live-cell imaging data reveal a novel phenomenon wherein collective behavior of 4-5 AFCs is required for clearing a single NC. By employing classical genetics, molecular biology, and yeast one-hybrid assay, we demonstrate that ecdysone modulates the phagocytic disposition of AFCs at two levels. It regulates the epithelial-mesenchymal transition of the AFCs through Serpent and modulates the phagocytic behavior of the AFCs through Croquemort and Draper. Our data provide unprecedented novel molecular insights into how ecdysone signaling reprograms AFCs toward a phagocytic fate.