Developmentaly regulated alternative RNA splicing of rat brain sodium channel mRNAs

Abstract
Two rat brain Na channel α-subunit cDNAs, named Rll and RIIA, have almost identical coding regions, with a divergence of only 36 nucleotides (0.6%) over a total length of 6015 residues. A cluster of 20 divergent esidues occurs within a 90 nucleotide segment of cDNA sequence. We now demonstrate that this 90 nucleotide segment is encoded twice in the RII/RIIA genomic sequence. Furthermore, the mutually exclusive selection of these two exons is developmentally regulated. Rll mRNAs are relativelyabundant at birth but are gradually replaced by RIIA mRNAs as development proceeds. The two mRNAs also appear to have different regional distributions in the developing rat brain. Strikingly, although 30 amino acids are encoded by each alternative exon, only aminoacid position 209 is altered b tween the two, specifying asparagine in Rll and aspartate in RIIA. Alternative RNA splicing may modulate the RII/RIIA sodium channel properties during neuronal development.