Novel isoforms of the sodium channels Nav1.8 and Nav1.5 are produced by a conserved mechanism in mouse and rat.
The voltage-gated sodium channel Na(v)1.8 is only expressed in subsets of neurons in dorsal root ganglia (DRG) and trigeminal and nodose ganglia. We have isolated mouse partial length Na(v)1.8 cDNA clones spanning the exon 17 sequence, which have 17 nucleotide substitutions and 12 predicted amino acid differences from the published sequence. The absence of a mutually exclusive alternative exon 17 was confirmed by sequencing 4.1 kilobases of genomic DNA spanning exons 16-18 of Scn10a. A novel cDNA isoform was identified, designated Na(v)1.8c, which results from alternative 3'-splice site selection at a CAG/CAG motif to exclude the codon for glutamine 1031 within the interdomain cytoplasmic loop IDII/III. The ratio of Na(v)1.8c (CAG-skipped) to Na(v)1.8 (CAG-inclusive) mRNA in mouse is approximately 2:1 in adult DRG, trigeminal ganglion, and neonatal DRG. A Na(v)1.8c isoform also occurs in rat DRG, but is less common. Of the two other tetrodotoxin-resistant channels, no analogous alternative splicing of mouse Na(v)1.9 was detected, whereas rare alternative splicing of Na(v)1.5 at a CAG/CAG motif resulted in the introduction of a CAG trinucleotide. This isoform, designated Na(v)1.5c, is conserved in rat and encodes an additional glutamine residue that disrupts a putative CK2 phosphorylation site. In summary, novel isoforms of Na(v)1.8 and Na(v)1.5 are each generated by alternative splicing at CAG/CAG motifs, which result in the absence or presence of predicted glutamine residues within the interdomain cytoplasmic loop IDII/III. Mutations of sodium channels within this cytoplasmic loop have previously been demonstrated to alter electrophysiological properties and cause cardiac arrhythmias and epilepsy.
Kerr
Niall C H
NC
Laboratories for Integrated Neuroscience and Endocrinology (LINE), Dorothy Hodgkin Building, Whitson Street, Bristol BS1 3NY, United Kingdom.
Holmes
Fiona E
FE
Wynick
David
D
D017398:Alternative Splicing; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D003062:Codon; D017124:Conserved Sequence; D003593:Cytoplasm / Q000378:metabolism; D018076:DNA, Complementary / Q000378:metabolism; D005091:Exons; D005973:Glutamine / Q000737:chemistry; D006801:Humans; D008297:Male; D051379:Mice; D008969:Molecular Sequence Data; D009124:Muscle Proteins / Q000737:chemistry*; D009154:Mutation; D062554:NAV1.5 Voltage-Gated Sodium Channel; D062559:NAV1.8 Voltage-Gated Sodium Channel; D009419:Nerve Tissue Proteins / Q000737:chemistry*; D016133:Polymerase Chain Reaction; D020033:Protein Isoforms; D017434:Protein Structure, Tertiary; D012313:RNA / Q000737:chemistry; D051381:Rats; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid; D015222:Sodium Channels / Q000737:chemistry*; D014018:Tissue Distribution
D003062:Codon; D018076:DNA, Complementary; D009124:Muscle Proteins; D062554:NAV1.5 Voltage-Gated Sodium Channel; D062559:NAV1.8 Voltage-Gated Sodium Channel; D009419:Nerve Tissue Proteins; D020033:Protein Isoforms; C568317:SCN10A protein, human; C568320:SCN5A protein, human; C568318:Scn10a protein, mouse; C568319:Scn10a protein, rat; C568321:Scn5a protein, mouse; C568322:Scn5a protein, rat; D015222:Sodium Channels; D005973:Glutamine; D012313:RNA