Expression of troponin C genes during development in the chicken

Expression of cardiac troponin C (C/STnC) and fast skeletal muscle troponin C (FTnC) genes during development was analyzed by in situ hybridization and Northern blot. At Hamburger-Hamilton stage 14, FTnC mRNA was detected in somites. At stage 20, FTnC mRNA was identified in truncus arteriosus. FTnC mRNA was undetectable in embryonic ventricle at the other developmental stages. This suggested that transcription of FTnC mRNA at stage 20 was stage and region-specific. At early stage 10, C/STnC mRNA was detected in truncus arteriosus, ventricle and vitelline veins at the proximal region where right and left veins bifurcate from ventricle. In the proximal region of vitelline vein, C/STnC mRNA was transcribed in both the rostral and caudal walls of the veins. The area of C/STnC gene expression in vitelline vein is wider than those of alpha-cardiac and smooth muscle actin genes (Ruzicka and Schwartz, J. Cell Biol. 107: 2575-2586, 1988). It is suggested that C/STnC plays an important role relating embryonic excitation-contraction-coupling in the wider area including vitelline vein. C/STnC mRNA was identified also in somites, embryonic breast muscle and adult breast muscle. Since C/STnC protein was undetectable in adult breast muscle by immunofluorescence microscopy (Toyota and Shimada, J. Cell Biol. 91: 497-504, 1981), the imbalance of C/STnC mRNA and protein levels suggested the operation of specific mechanisms that separately regulated the accumulation of C/STnC mRNA and protein.