Structure and evolution of the alternatively spliced fast troponin T isoform gene

The vertebrate fast skeletal muscle troponin T gene, TnTf, produces a compl exity of isoforms through differential mRNA splicing. The mechanisms that r egulate splicing and the physiological significance of TnTf isoforms are po orly understood. To investigate these questions, we have determined the com plete sequence structure of the quail TnTf gene, and we have characterized the developmental expression of alternatively spliced TnTf mRNAs in quail e mbryonic muscles. We report the following: 1) the quail TnTf gene is signif icantly larger than the rat TnTf gene and has 8 non-homologous exons, inclu ding a pectoral muscle-specific set of alternatively spliced exons; 2) spec ific sequences are implicated in regulated exon splicing; 3) a 900-base pai r sequence element, composed primarily of intron sequence flanking the pect oral muscle-specific exons, is tandemly repeated 4 times and once partially , providing direct evidence that the pectoral-specific TnT exon domain aros e by intragenic duplications; 4) a chicken repeat 1 retrotransposon element resides upstream of this repeated intronic/pectoral exon sequence domain E md is implicated in transposition of this element into an ancestral genome; and 5) a large set of novel isoforms, produced by regulated exon splicing, is expressed in quail muscles, providing insights into the developmental r egulation, physiological function, and evolution of the vertebrate TnTf iso forms.