Regulation of troponin T expression during muscle development in sea breamSparus auratusLinnaeus: the potential role of thyroid hormones

Abstract

SUMMARY In the sea bream Sparus auratus three stage-specific fast troponin T (fTnT) isoforms have been cloned and correspond to embryonic-, larval- and adult-specific isoforms. Characterisation, using database searches, of the putative genomic organisation of Fugu rubripes and Tetraodon nigroviridis fTnT indicates that alternative exon splicing in the 5 region of the gene generates the different isoforms. Moreover, comparison of teleost fTnTs suggests that alternative splicing of fTnT appears to be common in teleosts. A different temporal expression pattern for each fTnT splice varotnt is found during sea bream development and probably relates to differing functional demands, as a highly acidic embryonic form (pI 5.16) is substituted by a basic larval form (pI 9.57). Thyroid hormones (THs), which play an important regulatory role in muscle development in flatfish and tetrapods,appear also to influence TnT gene expression in the sea bream. However, THs have a divergent action on different sea bream TnT genes and although the slow isoform (sTnT1) is TH-responsive, fTnT, sTnT2 and the itronless isoform (iTnT) are unaffected. The present results taken together with those published for flatfish seem to suggest differences may exist in the regulation of larval muscle development in teleosts.

Troponin T isoform expression is modulated during Atlantic Halibut metamorphosis

“…2A), in a way similar to that previously reported in S. auratus , a perciform and also in other vertebrates [4,10-13], [38-50]. In the halibut the number of alternatively spliced fTnT isoforms are the same as found in Tetraodon and S. auratus [5]. In common with Tetraodon efTnT , exon V is spliced in and exon IV is spliced out (Fig.…”

“…1). As observed for the fTnT gene of S. auratus [5], halibut fTnT is also expressed in adult red muscle. In fact, the expression of teleost fast-specific genes in red muscle seems to be a common feature in teleost species [36,37].…”

“…The putative Tetraodon and deduced halibut fTnT gene is composed of 14 exons (Fig. 2A) as previously described for the sea bream [5]. The efTnThh isoform is composed of exons I to III and V to XIV (Fig.…”

“…In tetrapods, three TnT genes exist, fast, slow and cardiac, expressed respectively in white (fast-twitch and glycolytic), red (slow-twitch and oxidative) and cardiac muscle. However, recent studies indicate that in teleosts a greater number of genes exist and at least two fast TnT ( fTnT ) and two slow TnT ( sTnT ) genes exist as well as an apparently teleost specific intronless TnT ( iTnT ) gene [5-7]. …”

“…We recently reported the existence of three stage specific fTnT transcripts in a teleost, the sea bream, namely embryonic, larval and adult which are splice variants of a single gene [5]. Moreover, in contrast to tetrapods, two paralogue sTnT genes ( sTnT1 and sTnT2 ) that exhibit developmental specific expression were also identified in sea bream [6].…”