209A Poster - 01. Cell Stress and cell death
Thursday April 07, 2:00 PM - 4:00 PM

Authors:
Tslil Braun; Shmuel Pietrokovski; Eli Arama

Affiliation: Department of Molecular Genetics, Weizmann Institute of Science, Rehovot, Israel

Keywords:
a. caspases; a. spermatogenesis

Caspases are the executioners of apoptotic cell death, but these proteases also promote a variety of non-lethal cellular process. The requirement of caspase activity for spermatid terminal differentiation in Drosophila, a process also known as spermatid individualization, as well as how these cells avoid death in the presence of active caspases, has been well established by our group and others in the past two decades. However, the precise role of caspases during the process of spermatid individualization is still unknown. Moreover, although dozens of caspase-dependent non-lethal cellular processes (CDPs) have been characterized so far, identifying the precise functions of caspases during these cellular processes remained largely elusive and has been highly challenging. Perhaps the main reason for the slow progress has been the need to identify specific caspase protein substrates and the consequence of their cleavage; in particular that caspase activity is restricted during CDPs and thus might only partially cleave some substrates.
To start addressing this question in spermatids, we first compiled a list of about 2,000 potential caspases substrates, mainly identified in several large proteomics studies of mammalian cultured cells undergoing apoptosis. We identified the Drosophila orthologs of these proteins and focused on those that are known to mediate cytoskeletal dynamics, a main feature of spermatid individualization, and in which the caspase cleavage site has been conserved. We then downregulated these genes in the male germ cells both in a wild type background and in the background of downregulation of the main effector caspase Drice. We then subjected the male flies to sterility tests. Of those, we mainly focused on the genes that produced synthetic sterility when downregulated together with drice, and which exhibited grossly normal spermatid maturation but failed to individualize. This approach yielded several potential caspase substrate candidates, which are now being further studied in depth for their roles during spermatid individualization.