Induction of Somites by Myosin mRNA

Abstract

The effects of the messenger for myosin heavy chain (26S mRNA) on postnodal explants of chick embryo blastoderm were studied. Somites do not differentiate in the post-nodal explants of chick embryo cultivated by New’s method. They are induced when postnodal pieces are cultivated in the presence of a 26S mRNA extracted from chick leg muscles or in the presence of myosin. 26S mRNA plus actinomycin D induces small somites. 26S mRNA of duck, rabbit, or trout induce somite structures often built up of cells separated by large spaces and joined around a large myocele. Crayfish 26S mRNA or chick myosin light chain induce columnar cells connected around a cavity. Liver or kidney mRNA do not induce. The induction process can be summarized as follows: 26S mRNA codes for myosin (heavy chain) and the myosin (heavy chain) induces the somites. Induction of somites by mRNA can occur in the presence of actinomycin D but not when there is mRNA plus puromycin. It does occur when myosin acts in the presence of puromycin. Myosin and its heavy chain are present in chick blastoderm before the appearance of somites. Induced somites are able to induce neural plates. We conclude that in normal development somites are induced by myosin.

Transition from Non-Muscle to Muscle Myosin Light Chains in Chick Embryo Development

“…The presence of myosin at these stages was already shown by Ebert [8] and Bolzern et al [9] and may be related to the active cellular movement. It was not surprising to find a non-muscle-type myosin.…”

“…In postnodal ex plants of chick embryos cut at the primitive streak stage 0.6 mm behind the Hensen's node, the mesoderm differentiates into me senchyme and blood islands. Adding to the medium mRNA coding for myosin heavy chain or myosin itself, extracted from em bryonic leg muscle, somites appeared in the mesoderm [9].…”