Genetic Analysis of Non-Apoptotic Programmed Cell Death

Abstract

Programmed cell death (PCD) serves a variety of key roles during development and homeostasis. In most cases, PCD occurs via apoptosis, a highly orchestrated process that is primarily dependent on the activity of caspase proteases. However, many cells die by a process that has been termed “autophagic cell death.” Autophagic cell death occurs predominantly in highly differentiated cells like muscles and neurons, and although there has been a lot of research done on autophagy, the process leading to the induction of autophagic cell death is poorly defined. The term PCD was coined in 1965 to describe the death of the intersegmental muscles (ISMs) of moths (Lockshin and Williams 1965). The ISMs are used by the developing adult to eclose (emerge) at the end of metamorphosis, after which these muscles initiate autophagic cell death (Schwartz et al. 1990). Expression of Acheron, a phylogenetically-conserved member of the Lupus antigen family of RNA-binding proteins, is induced approximately 1000-fold when the ISMs become committed to die (Wang et al. 2009). Acheron serves as a survival protein to protect the cells until the time of eclosion, after which it is degraded (Sheel et al. 2016). RNA interference screening methods can be used to inhibit the activity of specific genes and identify genes that affect cell death in insect muscles. I used the fruit fly model organism Drosophila melanogaster because it has exceptional tools for genetic analysis. Rather than employ abdominal muscles to perform the eclosion behavior, flies utilize a set of muscles in the head known as the ptilinal muscles. Like the ISMs, following eclosion the ptilinal muscles die by a process controlled by Acheron (Sheel et al. 2016). Little is known about the molecular mechanisms that mediate autophagic cell death. Since non-dying cells can undergo autophagy it is not clear how autophagy is regulated to become part of the killing mechanism (Fuchs and Steller 2011). This project focuses on studying Acheron expression in D. melanogaster and identifying specific proteins that are essential for autophagic cell death.