Differential expression of a novel isoform of alpha-tropomyosin in cardiac and skeletal muscle of the Mexican axolotl (Ambystoma mexicanum).

Alternative mRNA splicing is a fundamental process in eukaryotes that contributes to tissue-specific and developmentally regulated patterns of tropomyosin (TM) gene expression. Northern blot analyses suggest the presence of multiple transcripts of tropomyosin in skeletal and cardiac muscle of adult Mexican axolotls. We have cloned and sequenced two tropomyosin cDNAs designated ATmC-1 and ATmC-2 from axolotl heart tissue and one TM cDNA from skeletal muscle, designated ATmS-1. Nucleotide sequence analyses suggest that ATmC-1 and ATmC-2 are the products of the same alpha-TM gene produced via alternate splicing, whereas ATmC-1 and ATmS-1 are the identical isoforms generated from the alpha-gene. RT-PCR analysis using isoform-specific primer pairs and detector oligonucleotides suggests that ATmC-2 is expressed predominantly in adult axolotl hearts. ATmC-2 is a novel isoform, which unlike ATmC-1 and other known striated muscle isoforms expresses exon 2a instead of exon 2b.