Novel developmentally regulated exon identified in the rat fast skeletal muscle troponin T gene.

In theory, the rat fast skeletal muscle troponin T gene can generate 64 different isoforms. Here we report the identification of a novel alternative exon (exon y) that increases the potential isoform variation to 128. The inclusion of exon y in fast skeletal muscle troponin T mRNA occurs in perinatal, but not adult, skeletal muscle. Exon y is located between exons 8 and 9. This is the first time that a developmentally regulated exon located amongst a set of alternatively spliced exons has been described. Exon y is included in two mRNA isoforms. The proteins that these mRNAs would encode have molecular masses greater than that of the largest fast skeletal muscle troponin T isoform lacking exon y. These two proteins correlate well in both size and pattern of expression with the two fast skeletal muscle troponin T isoforms expressed in perinatal skeletal muscle. These results indicate that there is coordinated regulation of the splicing of exon y with other alternative exons.