Neuron-specific expression of a synaptotagmin gene in the sea urchin Strongylocentrotus purpuratus

Interest in chordate evolution has emphasized a need for a better understanding of the comparative neuroanatomy of invertebrate deuterostomes. However, molecular and genetic approaches to neurobiological studies in these groups are hampered by a lack of neuron‐specific molecular markers. A monoclonal antibody, 1E11, is neuron specific and is useful in identification of neural structures in larvae and adults of echinoderms, hemichordates, and urochordates. To identify a neuron‐specific gene product, we have characterized the antigen recognized by 1E11. In immunoblots and immunoprecipitations of neural tissue from adult Strongylocentrotus purpuratus, 1E11 recognizes a 57‐kDa band. Tandem mass spectrometry of trypsin digests of the 57‐kDa band permitted peptide mass mapping and sequencing of five peptides. All of the sequenced peptides, and 12 additional mass‐mapped peptides, are found within the open reading frame of a cDNA encoding synaptotagmin B (Sp‐SynB). In situ RNA hybridizations with synaptotagmin B probes with S. purpuratus larvae reveal a pattern of expression that is similar to that revealed by the antibody 1E11. Antibodies produced against a bacterially expressed Sp‐SynB protein recognize a 57‐kDa protein and colocalize with 1E11. When a full‐length Sp‐SynB cDNA is expressed in chicken embryonic cells, the cells become immunoreactive to 1E11. We conclude that synaptotagmin B is a gene expressed in neurons that has conserved epitopes in other invertebrate deuterostomes. J. Comp. Neurol. 496:244–251, 2006. © 2006 Wiley‐Liss, Inc.