FBF/PUF and CYB-1/Cyclin B Proteins Promote Sperm Viability by Inhibiting Apoptosis in C. elegans Germline

Abstract

Using the nematode Caenorhabditis elegans as a model organism, I investigated the role of FBF (Fem-3-Binding Factor) and CYB-1 (one of three B-type Cyclins) proteins in the survival of sperm cells. FBF proteins (FBF-1 and FBF-2) play a role in the maintenance of germline stem cells, while CYB-1 regulates the cell cycle. Previous research revealed in the fbf-1 fbf-2 double mutant, only sperm cells are present with no oocytes or germline stem cells. In this study, it is hypothesized that both FBFs and CYB-1 proteins are required for sperm cell maintenance by repressing apoptosis mediated by CED-4 and/or MPK-1. CED-4 is a pro-apoptotic protein that initiates apoptosis, and MPK-1 plays a role in germ cell apoptosis. To test this hypothesis, I employed two triple mutant strains – fbf-1 fbf-2; ced-4 and fbf-1 fbf-2; mpk-1. Specifically, I performed cyb-1 RNAi in these mutants from L1 stages and counted the number of sperm at 20 °C after staining dissected gonads with anti-MSP (sperm cell marker). I found that cyb-1 RNAi eliminated sperm cells in the fbf-1 fbf-2; mpk-1, but not in the fbf-1 fbf-2; ced-4 mutant germlines. These results indicate that FBFs and CYB-1 proteins protect sperm cells by inhibiting CED-4-mediated apoptosis in the C. elegans germline. Importantly, these regulators are also highly expressed in the reproductive systems of other organisms, including humans. Therefore, these findings and future work may provide insight into germ cell maintenance in humans and other organisms.