Molecular characterization and gene expression of synaptosome-associated protein-25 (SNAP-25) in the brain during both seaward and homeward migrations of chum salmon Oncorhynchus keta

Abstract

It is generally accepted that information about some of the odorants in the natal streams of anadromous Pacific salmon (Genus Oncorhynchus) is imprinted during their seaward migration, and that anadromous Pacific salmon use olfaction to identify their natal streams during the homeward migration. However, little is known about the molecular mechanisms of the various pre-synaptic functions that are important for olfactory imprinting and memory retrieval in the salmon brain. Synaptosome-associated protein-25 (SNAP-25) mediates pre-synaptic vesicle exocytosis and regulates synaptic transmission and neuronal plasticity. Despite the importance of synaptic plasticity for memorization, the expression of SNAP-25 in the salmon brain is not well understood. In this study, snap25 expression was detected in chum salmon (O. keta) brains using molecular biological techniques. Two cDNAs encoding salmon SNAP-25 were isolated and sequenced (SNAP-25a and SNAP-25b). These cDNAs encoded proteins with 204 amino acid residues, which showed marked homology with each other (97%). The protein and nucleotide sequences demonstrated a high level of homology between salmon SNAP-25s and those of other teleost species. By quantitative PCR, the expression of snap25a and snap25b was detected in all regions of the salmon brain, especially in the telencephalon. The expression levels of snap25a in the olfactory blub were higher during seaward migration than in upriver and post-upriver migrations, reflecting synaptogenesis in the olfactory nervous system, and snap25b in the telencephalon was increased during upriver period. Our results indicated that snap25s gene is involved in synaptic plasticity for olfactory imprinting and/or olfactory memory retrieval in Pacific salmon.

Elevated CO2 impairs olfactory‐mediated neural and behavioral responses and gene expression in ocean‐phase coho salmon (Oncorhynchus kisutch)

“…The significant increase in hcn2 , which plays critical roles in membrane excitability, integration of synaptic inputs, and the generation of membrane potential oscillations within the olfactory bulb, suggests alterations in signal modulation under elevated CO 2 conditions (He, Chen, Li, & Hu, ). Two other genes associated with synaptic transmission and modulation of neuronal GABA signaling through Cl − transport, snap25 and kcc1 , also showed significant increases in expression further suggesting altered neuronal signaling within the olfactory bulbs (Abe, Minowa, & Kudo, ; Delgado‐Martínez, Nehring, & Sørensen, ; Delpire, ; Wang et al, ). The increases in slc6a13 and slc38a3 , which can serve roles in taurine/GABA uptake and glutamate uptake needed for GABA synthesis, respectively, potentially indicate increased production or uptake of GABA as a compensatory response by the bulb neurons (Chan et al, ; Scimemi, ).…”

Gene expression of neuronal soluble N‐ethylmaleimide‐sensitive factor attachment protein receptor complex components in the olfactory organ and brain during seaward and homeward migration by pink salmon (Oncorhynchus gorbuscha)

“…The sources of primers were Abe et al ., 2018 for Snap25s and Abe & Kudo, 2019 for Stx1s and Vamp2 .…”

“…The oligonucleotides used as PCR primers are shown in Table 2. These primer sets used for TA cloning were described in detail in our previous studies that characterized chum salmon snare genes (Abe et al ., 2018; Abe & Kudo, 2019). Nucleotide sequences corresponding to the primers for quantitative real‐time PCR (qPCR) were identical between pink and chum salmon, and primer sets for qPCR were then applied.…”

“…The receptor gene expression of the neurotransmitter N ‐methyl‐ d ‐aspartate (NMDA) was shown to be associated with imprinting and/or the retrieval of imprinted memories in the brain of chum salmon ( O. keta ; Ueda et al ., 2016). We previously suggested that relationships exist between neuronal development and plasticity and the components of the soluble N ‐ethylmaleimide‐sensitive factor attachment protein receptor (Snare) complex in the chum salmon CNS (Abe et al ., 2018; Abe & Kudo, 2019). The neuronal SNARE complex regulates synaptic vesicle docking, membrane fusion and exocytosis (Lin & Scheller, 2000).…”

“…The neuronal SNARE complex regulates synaptic vesicle docking, membrane fusion and exocytosis (Lin & Scheller, 2000). Core components of Snare, synaptosome‐associated protein 25 (Snap25), syntaxin‐1 (Stx1) and vesicle‐associated membrane protein 2 (Vamp2) mRNAs, were found to be more strongly expressed in the chum salmon olfactory nervous system [the olfactory rosette (OR), olfactory bulb (OB) and telencephalon] during migration stages, which was related to imprinting and/or retrieval (Abe et al ., 2018; Abe & Kudo, 2019). Pre‐ and postsynaptic neuronal molecules are expected to reflect differences in age, maturation stages and the ecological features of the salmon life cycle.…”