Muscle gene activation by induction and the nonrequirement for cell division.

We are investigating the mechanism by which animal cells of an amphibian blastula are induced to differentiate as muscle after contact with blastula vegetal cells. After briefly summarizing previous work on this system, we have asked whether this response of animal cells to vegetal induction requires cell division. Animal and vegetal parts of a blastula were placed in contact with each other, and the resulting conjugates cultured in medium containing a sufficient concentration of colchicine or cytochalasin B to inhibit cell division. Muscle differentiation, as indicated by cardiac actin gene transcription, is induced when cell division is inhibited, though at a substantially reduced rate. However, cytoskeletal actin gene transcription, which does not depend on induction, is also much reduced under the same inhibitory conditions. We conclude that, although the cell division inhibitors seem to reduce all gene transcription, they have no preferential effect on the response to induction, and therefore that this process does not require cytoplasmic or nuclear division.