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 α-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 Ca2+-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 Ca2+ 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.
All Science Journal Classification (ASJC) codes
- Molecular Biology
- Developmental Biology
- Cell Biology