Engulfment Receptors in Programmed Cell Death in the Drosophila Ovary. Tracy L. Meehan, Allison Timmons, Jon Iker Etchegaray, Jeffrey Taylor, Olivia Rudnicki, Sarah Yunes, Kim McCall. Department of Biology, Boston University, Boston, MA.

   Programmed cell death is essential for an organisms development and homeostasis to dispose of unwanted or diseased cells. Upon starvation, the nurse cells undergo apoptosis and are engulfed by the surrounding follicle cells. We studied the role of known engulfment receptors, Draper and integrins, in the role of starvation-induced cell death. Draper is the Drosophila homolog of the C. elegans engulfment receptor, CED-1. Integrins, on the other hand, have historically been studied for their roles in migration and cell signaling; only recently have they been shown to play a role in engulfment in D. melanogaster. Both drpr null flies and dsRNA drpr knockdown specifically in the follicle cells resulted in defective mid-oogenesis death. The follicle cells in these mutant egg chambers did not enlarge appropriately and died prematurely. Drapers main role was found to be activating JNK, as expression of activated hep (JNK kinase) suppressed the Draper mutant phenotype. To determine if integrins are required for engulfment in the ovary, we knocked down integrin PS, the main subunit in Drosophila, effectively knocking out the majority of all integrins in follicle cells. These egg chambers showed defective egg chambers very similar to those found in drpr RNAi flies. We are currently working on immunocytochemistry experiments to determine if there are subtle differences between PS and Draper mutants. Previous work has shown that integrins can activate the JNK pathway, which activates Draper in our system. To determine if integrins work through the JNK pathway to up-regulate Draper in the ovary, we stained PS mutant egg chambers with Draper and Draper mutant egg chambers with integrins. We found that Draper is still up-regulated in PS mutant egg chambers and integrins are still up-regulated in Draper mutant egg chambers. We are currently screening candidate genes from the JNK and known engulfment pathways and the integrin subunits to understand the complete pathway occurring in mid-oogenesis engulfment. Future studies will investigate how integrins and Draper interact.