Molecular characterization and gene expression of syntaxin-1 and VAMP2 in the olfactory organ and brain during both seaward and homeward migrations of chum salmon, Oncorhynchus keta.

Anadromous Pacific salmon (Genus Oncorhynchus) imprint odorants from their natal streams during their seaward migration, and adult salmon use olfaction to identify their natal streams during their homeward migration. However, little is known about the molecular mechanisms of olfactory imprinting in the salmon nervous system. Our previous study suggested that the snap25s gene (encoding a soluble N-ethylmaleimide-sensitive factor attachment protein receptor [SNARE] protein) is involved in pre-synaptic functions for olfactory imprinting and/or olfactory memory retrieval in chum salmon (O. keta). In this study, the expression of other SNARE proteins was analyzed in chum salmon brains. Three cDNAs, encoding salmon SNARE proteins (STX-1a, STX-1b, and VAMP2), were isolated and sequenced, which are well-conserved among vertebrates. Quantitative PCR detected the expression of stx1s and vamp2 in all regions of the brain, and especially highly in the olfactory bulb (OB) and telencephalon. The expression levels of snares in the olfactory rosette (OR) were higher during seaward migration than in adult life stages, subsequently vamp2 in the OB and telencephalon increased during seaward migration, corresponding well with development of the olfactory nervous system. Both stx1s in the OB and stx1b in the telencephalon were elevated in the seaward period, whereas stx1a in the telencephalon increased continuously until the feeding period. Both stx1s in the telencephalon increased in the last phase of upriver migration, possibly related to the retrieval of imprinted memory. Our results indicated the involvement and distinct roles of upregulated snares in synaptic plasticity for olfactory imprinting and/or olfactory memory retrieval in Pacific salmon.