Worm Breeder's Gazette 14(1): 55 (October 1, 1995)
These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.
Department of Biology, Johns Hopkins University, Baltimore, MD 21218
Neurexins are a family of neuronal transmembrane proteins located at presynaptic terminals (Ushkaryov et al., Science 257: 50 (1992)). Their biochemical affinity to synaptotagmin, and to alpha-latrotoxin, a black widow spider venom toxin that promotes calcium-independent transmitter release, indicates that neurexins play a role in regulated exocytosis at nerve terminals. Neurexins have a large extracellular domain consisting of laminin G domains and EGF domains, suggesting that neurexins also interact with the extracellular matrix or postsynaptic cells. More than 600 neurexin variants, most of them created by alternative splicing of mini exons in the extracellular domain, are present in rat brain. At least some isoforms are differentially expressed (Ullrich et al., Neuron 14: 497 (1995)). Taken together, these features suggest a role for neurexins in a combinatorial synaptic recognition process. We have cloned neurexin homologues from Caenorhabditis to study their role in transmitter release and in synaptic recognition. Genomic clones of a C.briggsae neurexin were isolated from Dave Baillie's library using a fragment identified by the Genome Project (WBG 13(2): 19); C.elegans clones were obtained by PCR with degenerate primers. Sequence analysis of partial clones, lacking the protein termini, reveals a predicted protein with the same domain organization as mammalian neurexins. The mammalian and Caenorhabditis neurexins are ~30% identical with similarities distributed throughout the length of the sequence. The three different known rat neurexins are more similar to each other than to the Caenorhabditis proteins. This suggests that these rat genes diverged from an ancestral neurexin gene after the divergence of chordates from nematodes, and therefore there possibly exists only one neurexin gene of this class in C.elegans. Our searches by PCR and low stringency hybridization have so far failed to identify further neurexin homologues. Reduced complexity of the neurexin family in Caenorhabditis is further indicated by the absence of mini exons in the G domains that are involved in creating the large variety of mammalian neurexins. We will determine the number of neurexin isoforms in C.elegans and analyze their expression pattern(s) to test whether there is a differential expression correlated with synaptic connectivity, as predicted for a synaptic recognition protein. We are also determining the position of the neurexin gene on the physical map to initiate a genetic analysis of neurexin function(s) in C.elegans.