TNNT2 is expressed in neonatal skeletal muscle, the alternative splicing of exon 5 exhibits a synchronized regulation to that in the heart in a species-specific manner. This phenomenon indicates that alternative splicing of TNNT2 pre-mRNA is under the control of a genetically built- in systemic biological clock. Posttranslational modifications Phosphorylation Ser2 of cTnT at the N terminus is constitutively phosphorylated by unknown mechanisms. cTnT has been found to be phosphorylated by PKC at Thr197, Ser201, Thr206, Ser208 and Thr287 in the C-terminal region. Phosphorylation of Thr206 alone was sufficient to reduce myofilament calcium sensitivity and force production. cTnT is also phosphorylated at Thr194 and Ser198 under stress conditions, leading to attenuated cardiomyocyte contractility. Phosphorylation of cTnT at Ser278 and Thr287 by ROCK-II was shown to decrease myosin ATPase activity and myofilament force development in skinned cardiac muscle. Table 1 summarizes the phosphorylation modifications of cTnT and possible functions. O-linked GlcNAcylation cTnT is increasingly modified at Ser190 by O-GlcNAcylation during the development of heart failure in rat, accompanied by decreased phosphorylation of Ser208. Proteolytic modification In apoptotic cardiomyocytes, cTnT was cleaved by caspase 3 to generate a 25-kDa N-terminal truncated fragment. This destructive fragmentation removes a part of the middle region tropomyosin binding site 1, leading to attenuation of the myofilament force production by decreasing the myosin ATPase activity. In cardiac muscle under stress conditions, cardiac TnT is cleaved by calpain I, restrictively removing the entire N-terminal variable region. This proteolytic modification of cTnT occurs in cardiac muscle in acute ischemia-reperfusion or pressure overload. The restrictively N-terminal truncated cTnT remains functional in the myofilaments and leads to reduced contractile velocity of the ventricular muscle, which extends the rapid ejection phase and results in an increase in stroke volume, especially under increased afterload. In vitro studies showed that N-terminal truncated cTnT preserved the overall cardiac myofilament calcium sensitivity and cooperativity, but altered TnT's binding affinities for tropomyosin, TnI and TnC proteins, and lead to slightly decreased maximum myosin ATPase activity and myofilament force production, which forms the basis of the selective decrease in contractile velocity of ventricular muscle to increase stroke volume without significant increase in energy expenditure. With the relatively short half life of cTnT in cardiomyocytes (3–4 days), the N-terminal truncated cTnT would be replaced by newly synthesized intact cTnT in several days. Therefore, this mechanism provides a reversible posttranslational regulation to modulate cardiac function in adaptation to stress conditions.