Correlation between the protein and mRNA levels for myosin light chains and tropomyosin subunits during chick fast muscle development in vivo.

Using myosin light chains and tropomyosin subunits as representative myofibrillar proteins, we have characterized their isoprotein forms and also correlated them with the accumulation of the corresponding mRNAs during development of a fast muscle in chicken, viz, pectoralis. Both slow and fast myosin light chain isoforms, except fast myosin light chain LC3, and the two subunits of tropomyosin are present in early embryonic muscle. During development, the slow myosin light chains and beta-tropomyosin appear in reduced amounts in pectoralis muscle and finally they disappear in adult muscle. Translation studies with total cellular RNA from developing muscle indicates that while the protein levels of the above isoforms, in general, correlate with the accumulation of corresponding mRNAs, for LC3, additional post-transcriptional control appears to modulate the expression of this isoprotein skeletal muscle development in vivo.