HUMAN CARDIAC TROPONIN-T - CLONING AND EXPRESSION OF NEW ISOFORMS IN THE NORMAL AND FAILING HEART

Troponin T, like many myofibrillar proteins, exists as multiple isofor ms encoded by distinct genes or generated by splicing of the same prim ary RNA transcript. We have previously cloned the first human cardiac troponin T (cTnT) cDNA and showed the differential expression of cTnT in cardiac and skeletal muscle during ontogenic development. In this w ork we located the human cTnT gene by means of fluorescent in situ hyb ridization to 1q32 and, by sequencing thirteen cDNAs isolated from a h uman fetal heart cDNA library, identified three new isoforms resulting from specific combinations of three variable regions in human cTnT cD NA. The first variable region is a 30-bp box located at the 5' end of the cDNA, which can be excised either totally or only from the first 3 bp onwards; the second is a codon which can be completely excised; an d the third is a 9-bp box in the 3' half of the cDNA, which can also b e excised either totally or only from the first 3 bp. The existence of the corresponding RNAs in fetal and adult ventricles was confirmed by RNase protection studies. No accumulation of the fetal isoforms was f ound in failing ventricles compared with controls.