[Molecular strategies involved in the control of gene expression during differentiation of muscle cells].

The initial step in muscle formation is the fusion of undifferentiated myoblasts into multinucleated myotubes which synthesize the specific proteins of the muscle. During this transition a whole series of genes are turned on. A simple explanation for this activation process is that each gene contains a structure which is common to all genes of the family and which is recognized by (a) specific factor(s). Experimental evidence supporting this model is described. Appearance of a new protein may not involve gene activation but be the result of a new mode of splicing as in the case of tropomyosins. Examples have been chosen to illustrate the various strategies used to control gene expression and provide the necessary diversity required during the process of muscle maturation. They include controlled expression of linked genes, coexpression of genes from unrelated phenotypes or alternative splicing of unique genes.