Analysis of a gene required for membrane fusion during nematode spermiogenesis

Abstract

C. elegans spermatids contain large vesicles called membranous organelles (MOs) that fuse with the plasma membrane during maturation to spermatozoa. This fusion is essential since mutations in the gene fer-1 block MO-plasma membrane fusion and result in abnormal spermatozoa. To determine the function of the fer-1 gene product during sperm maturation, I have cloned and sequenced the gene and several cDNAs. fer-1 is approximately 8.6kb in length and encodes a 6.3kb sperm-specific transcript. In situ hybridization experiments have shown fer-1 expression is limited to the primary spermatocytes, the cells in which the MOs are formed. fer-1 is predicted to encode a 235kD basic integral membrane protein (FER-1) that is highly charged and rich in lysine and glutamic acid. Database searches revealed FER-1 is similar to several predicted human proteins of unknown function. Mutations have been identified for four of the eleven fer-1 alleles, all of which cause amino acid changes in this predicted protein. FER-1 contains no recognizable functional motifs other than a single transmembrane domain at the C-terminus, a feature common to viral membrane fusion proteins. Antibodies raised against FER-1 and used for immunolocalization and western blot experiments did not yield reliable results. The work presented in this dissertation gives some evidence for my hypothesis that FER-1 is a membrane fusion protein, although the membrane fusion defect observed could be an indirect result of fer-1 mutations.