Chicken Perinatal Troponin Ts Are Generated by a Combination of Novel and Phylogenetically Conserved Alternative Splicing Pathways

During perinatal development, avian and mammalian skeletal muscles express a novel set of troponin T (TnT) isoforms with higher M rs and more acidic p Is than their adult counterparts. In mammals, these TnTs result from the incorporation of a developmentally regulated 5′-fetal exon into fast TnT mRNAs. To determine whether chicken perinatal TnTs are generated by a similar mechanism, we sequenced 40 chicken TnT 5′-cDNAs from perinatal and adult pectoralis. Evidence for five 5′-exons not present in the mammalian gene was found, including one, y, whose splicing is developmentally regulated. Although none of these new exons are homologous with the mammalian fetal exon, their alternative splicing, superimposed on three conserved splicing patterns of the phylogenetically shared 5′-exons, generates the chicken perinatal TnT isoforms. These observations indicate that chicken, and most likely other avian species, evolved an independent 5′-alternative splicing mechanism to generate perinatal TnTs that have the same biophysical, and presumably functional, properties as their mammalian homologs.