α-Smooth muscle actin is transiently expressed in embryonic rat cardiac and skeletal muscles

Actin isoform expression may change during development, and in certain physiological, experimental and pathological situations. It is accepted that during sarcomeric (skeletal and cardiac) muscle development, the α-skeletal and α-cardiac isoforms of actin accumulate rapidly at the onset of muscle fibre formation, while there is a rapid fall in the expression of nonmuscle (β and γ) actin isoforms. Here we show that, before birth, both skeletal and myocardial cells express significant amounts of α-smooth muscle actin mRNA and protein. This expression is transient and disappears over the 1–7 days following birth. Our findings show that the program regulating actin isoform expression in sarcomeric muscle development is complex and that α-smooth muscle actin participates in this process. © 1988, International Society of Differentiation. All rights reserved