The synthesis of myosin mRNA and myosin in the early development of Xenopus laevis embryos

A biochemical approach was used to detect the appearance of the heavy chain of skeletal myosin (HCSM) and myosin mRNA during the early development of Xenopus laevis embryos. An antibody against the HCSM of adult X. laevis muscles was biochemically characterized and shown to be monospecific. This anti-myosin antibody reacted with embryonic polysomes synthesizing myosin and with tadpole tail myosin. This indicates that the myosins of adult muscles, early embryonic muscles and tadpole tails are sufficiently homologous to share some antigenic determinants. Polysomes from various stages of X. laevis embryogenesis were reacted with the anti-myosin antibody. Analysis of these reactions showed that myosin synthesis begins in stage 20 embryos, in which about 7 somites have segregated. The RNA from stage 12, stage 16/17 and stage 20 embryos was then analyzed for the presence of the heavy chain myosin mRNA in order to determine whether the synthesis of myosin is under translational or transcriptional control. Total RNA preparations from staged embryos were fractionated on oligo(dT)-cellulose columns and fractions that did and did not bind were translated in a wheat germ cell-free protein synthesizing system. The translational products were precipitated with the anti-myosin antibody and characterized biochemically. Myosin mRNA was detected by this method in stage 16/17 embryos. We conclude that somite segregation results in the appearance of new myosin mRNA molecules in X. laevis embryos. It seems likely, by all the evidence considered, that a large pool of untranslated myosin mRNA molecules is not responsible for muscle myosin synthesis. Therefore, the synthesis of certain proteins in early development is under transcriptional control.Science, Faculty ofZoology, Department ofGraduat