COEXPRESSION OF ALPHA-SARCOMERIC ACTIN, ALPHA-SMOOTH MUSCLE ACTIN AND DESMIN DURING MYOGENESIS IN RAT AND MOUSE EMBRYOS .1. SKELETAL-MUSCLE

Expression of vimentin, desmin, α-sarcomeric and α-smooth muscle actins in embryonic tissues of rat and mice was examined using an immunohistochemical approach. The results showed a similarity in the expression of desmin and α-actin isoforms (α-sr and α-sm) in skeletal muscle cells during murine feto-embryonic development. In the two species, coexpression of α-sr and α-sm actins has been observed in cardiomyoblasts, myotomal myoblasts and myotubes. The intensity of α-sm actin expression decreased during the terminal steps of myogenesis and disappeared completely in mature cardiomyocytes and myofibres. Desmin was expressed in all prefusion myoblasts (type 1 and 2 myoblasts), myotubes, and in myofibres. The appearance of desmin in myoblasts of somites preceded by a few hours the expression of the α-actins (α-sr and α-sm). Our study on vimentin expression, limited to rat embryos, revealed that somite premyoblasts expressed only vimentin, type 1 myoblasts expressed vimentin and desmin, and type 2 myoblasts (rhabdomyoblasts) expressed desmin and α-actins (α-sr and α-sm). Our study demonstrates the resemblance between feto-embryonic myogenesis and myogenic neoplastic differentiation: desmin appears before the α-actins in embryonic myoblasts, and can be considered as a marker of an initial step in myogenic differentiation, α-sm actin, considered as a striated muscle cell feto-embryonic actin, is expressed transiently in skeletal myoblasts and cardiomyoblasts during development and reappears during neoplastic transformation of skeletal muscle. © 1990, International Society of Differentiation. All rights reserved.