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Dev Biol. 2008 Oct 1;322(1):65-73. doi: 10.1016/j.ydbio.2008.07.007. Epub 2008 Jul 16.

Targeted disruption of the cardiac troponin T gene causes sarcomere disassembly and defects in heartbeat within the early mouse embryo.

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Department of Developmental Molecular Anatomy, Graduate School of Medical Science, Kyushu University, 3-1-1 Maidashi, Fukuoka 812-8582, Japan.


Cardiac troponin T (cTnT) is a component of the troponin (Tn) complex in cardiac myocytes, and plays a regulatory role in cardiac muscle contraction by anchoring two other Tn components, troponin I (TnI) and troponin C, to tropomyosin (Tm) on the thin filaments. In order to determine the in vivo function of cTnT, we created a null cTnT allele in the mouse TNNT2 locus. In cTnT-deficient (cTnT(-/-)) cardiac myocytes, the thick and thin filaments and alpha-actinin-positive Z-disk-like structures were not assembled into sarcomere, causing early embryonic lethality due to a lack of heartbeats. TnI was dissociated from Tm in the thin filaments without cTnT. In spite of loss of Tn on the thin filaments, the cTnT(-/-) cardiac myocytes showed regular Ca(2+)-transients. These findings indicate that cTnT plays a critical role in sarcomere assembly during myofibrillogenesis in the embryonic heart, and also indicate that the membrane excitation and intracellular Ca(2+) handling systems develop independently of the contractile system. In contrast, heterozygous cTnT(+/-) mice had a normal life span with no structural and functional abnormalities in their hearts, suggesting that haploinsufficiency could not be a potential cause of cardiomyopathies, known to be associated with a variety of mutations in the TNNT2 locus.

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