both fast and slow fiber dominant skeletal muscles. The inclusion of more N-terminal exons increases the negative charge that tunes the overall molecular conformation of fsTnT and alters interaction with TnI, TnC and tropomyosin. The alternative splicing-based addition of N-terminal negative charge in fsTnT also contributes to the tolerance to acidosis. Alternative splicing of the two C-terminal mutually exclusive exons 16 and 17 appears also regulated during development. Exon 17 with a sequence more similar to the counterpart segment in ssTnT and cTnT is predominantly expressed in embryonic and neonatal fsTnT. Exon 16 of fsTnT was only found in adult skeletal muscles. Exons 16 and 17 both encode a 14 amino acids peptide fragment residing in the α-helix interfacing with TnI and TnC. Protein interaction studies revealed that incorporation of exon 17 weakened binding of fsTnT to TnC and tropomyosin. Therefore, alternative splicing of exons 16 and 17 regulates the binding of fsTnT with TnI, possibly TnC, and thus tunes the function of the troponin complex and skeletal muscle contractility during development. Avian Tnnt3 gene with additional alternatively spliced exons has unique expression pattern. The seven P exons are specifically expressed in pectoral muscles but not leg muscles. During post hatch development of the avian pectoral muscles, the segment encoded by the P exons (named Tx from the original annotation of the coding exons as an x exon) is up-regulated and included predominantly in fsTnT of adult pectoral muscles. Each P exon encodes a pentapeptide AHH(A/E)A. The Tx segment of adult fsTnT in avian orders of Galliformes and Craciformes contains 7-9 H(A/E)AAH repeats that possess high affinity binding to transition metal ions Cu(II), Ni(II), Zn(II) and Co(II). The Tx segment of chicken breast muscle fsTnT also a binding capacity for calcium, presumably serves as a calcium reservoir in avian fast pectoral muscles. Together with more N-terminal negative charges, this function may contribute to the higher calcium sensitivity of chicken breast muscle than that of leg muscle. The switch of high to low molecular weight splice forms occurs in avian leg muscles during post hatching development similar to that in developing mammalian skeletal muscles. Early during post hatch development of chicken pectoral muscles, fsTnT also shows a high to low molecular weight switch. However, around 28 days after hatch, fsTnT with Tx segment spliced-in is rapidly up-regulated and becomes the major fsTnT splice form in adult pectoral muscles. Deficiency of ssTnT