DIFFERENTIAL EXPRESSION OF TRANSCRIPTS FROM SYB, A DROSOPHILA-MELANOGASTER GENE ENCODING VAMP (SYNAPTOBREVIN) THAT IS ABUNDANT IN NONNEURONAL CELLS

VAMP (synaptobrevin) is a highly conserved membrane protein originally described as a component of brain synaptic vesicles. The Drosophila melanogaster VAMP-encoding gene (syb) comprises five exons. Splicing exons 1,2,3,4,5 (syb-b) results in a protein with a C-terminal hydrophobic domain and a negligible intraluminal domain. Splicing exons 1,2,3,5 (syb-a) predicts a protein with a 20-amino-acid luminal domain at the C terminus. The ratio of syb-a to syb-b transcripts is highly regulated during development. The syb transcripts show no enrichment in the nervous system and are present in very early embryos, well before neurogenesis. The greatest concentration of syb transcripts was found in cells of the gut and malpighian tubules. Thus, syb may have a general role in membrane trafficking and, perhaps, a role in the secretion of digestive enzymes.