Thesis (Ph.D.)--University of Rochester. School of Medicine & Dentistry. Dept. of Biomedical Genetics, 2012.
Apoptosis and immune responses are crucial for tissue and organismal homeostasis in metazoans. Loss of proper regulation of these processes can cause serious defects in health and eventually lead to organismal death. Drosophila melanogaster is an excellent model system to study apoptosis and immune responses. By using both loss-of-function and gain-of-function approaches, I identified and characterized a novel gene, dwdr40, as a regulator of apoptosis and innate immunity in Drosophila melanogaster. I found that loss of functional dWDR40 resulted in pupal lethality and blocked, or at least delayed, the programmed cell death in many different tissues during pupal development. On the other hand, overexpression of dwdr40 in developing imaginal discs was sufficient to induce apoptosis, thereby restricting tissue and organ growth. Genetic epistasis analysis placed dWDR40 in the core apoptotic signaling cascade between the proapoptotic Reaper-Hid-Grim and the apoptosome. Based on the results from genetic and biochemical analysis, I propose that in order to execute developmental apoptosis, especially during pupal development, expression of dWDR40 increases upon ecdysone peaks along with other core components in the canonical apoptosis pathway.
Interestingly, I observed that homozygous mutants for dwdr40 expressed significantly lower antimicrobial peptides (AMPs) after being challenged with Serratia marcescens, suggesting that dwdr40 is required for proper immune response. In Drosophila, DIAP2, which is structurally similar to DIAP1, is indispensible for induction of AMPs after gram-negative bacterial challenge. I found that DIAP2 protein level was significantly lowered in the loss-of-function mutants for dwdr40. These results establish that dwdr40 is a novel regulator for both apoptosis and immunity.
In chapter 3, I will also discuss preliminary results showing that targeted expression of dwdr40 in the adult fatbody extended lifespan and increased resistance to starvation stress, possibly by modulating the TOR signaling pathway. Together, the current work described in this thesis demonstrates the importance of the evolutionary conserved gene, dwdr40, in the regulation of cell death, immunity and aging.
