[
International C. elegans Meeting,
1999]
Type I diabetes is an autoimmune disease in which the immune system targets antigens in the insulin-producing pancreatic beta-cells. The Islet Cell Antigen of 69 Kd (ICA69) was discovered by screening islet cell expression libraries with serum from diabetic rats or human patients. The protein exhibits no significant homology with proteins of known function, except for the presence of a putative coiled coil motif possibly implicated in protein-protein interactions. Based on its amino acid sequence, ICA69 is predicted to be a cytosolic soluble protein. Only one ICA69 gene seems to exist in mouse (478 aa), rat (480 aa) and human (483 aa); these exhibit 87% overall identity. In mouse, the ICA69 protein is expressed in most organs, but is most abundant in tissues rich in neuroendocrine or secretory cells such as brain, pancreas and stomach mucosa. The C32E8.7 (418 aa) predicted gene encodes a C.elegans homolog of ICA69 (33% overall identity with human ICA69, including a stretch of 280 aa with 58% conservation). Using a GFP reporter in transgenic C.elegans , we found that the C32E8.7 promoter is specifically expressed in all C.elegans neurons; the timing of promoter activity coincides with the appearance of differentiated neurons during embryogenesis (~400 minutes). Because: 1) most diabetes autoantigens are components of the insulin secretory granules; 2) The high levels of ICA69 expression in neuroendocrine/secretory tissues; and 3) the C.elegans homolog of ICA69 is expressed in differentiated neurons, we hypothesized that ICA69 is involved in regulated exocytosis which mediates, for example, insulin secretion by pancreatic beta-cells and neurotransmitter release by neurons. In collaboration with Prof. Plasterk (Amsterdam, NL), we have isolated a C32E8.7 mutant (NL2003) in which nucleotides -395 to +2276 (262 codons) have been deleted. The NL2003 mutant exhibits no overt phenotype. However, we have observed a slight shortening of life span, and preliminary experiments suggest that the mutant is slightly resistant to aldicarb, an inhibitor of acetylcholinesterase. This later observation would support our hypothesis that ICA69, and its C.elegans homolog, is involved in exocytosis.