Molecular evolution of the synapsin gene family

Synapsins, a family of synaptic vesicle proteins, play a crucial role in th e regulation of neurotransmission and synaptogenesis. They have been identi fied in a variety of invertebrate and vertebrate species, including human, rat (Rattus norvegicus), cow (Bos taurus), longfin squid (Loligo pealei), a nd fruit fly (Drosophila melanogaster). Here, synapsins were cloned from th ree additional species: frog (Xenopus laevis), lamprey (Lampetra fluviatili s), and nematode (Caenorhabditis elegans). Synapsin protein sequences from all these species were then used to explore the molecular phylogeny of thes e important neuronal, phosphoproteins. The ancestral condition of a single synapsin gene probably gave rise to the vertebrate synapsin gene family com prised of at least three synapsin genes (I, II, and III) in higher vertebra tes. Synapsins possess multiple domains, which have evolved at different ra tes throughout evolution. In invertebrate synapsins, the most conserved dom ains are C and E. During the evolution of vertebrates, at least two gene du plication events are hypothesized to have given rise to the synapsin gene f amily. This was accompanied by the emergence of an additional conserved dom ain, termed A. (C) 1999 Wiley-Liss, Inc.