The Chromosomal Assignment of Muscle-Specific Genes
Investigations during recent years indicate that the program of gene expression during the differentiation of the striated muscles is much more complex than had been suggested from earlier studies. It is now evident that muscle differentiation is accompanied by successive transitions from embryonic to fetal to adult isoforms of closely related contractile proteins, as well as transitions from fast to slow muscle-specific isoforms, which are under the control of physiological and hormonal factors (381,588,592). Moreover, some contractile proteins seem to be the main adult isoform in one muscle and a juvenile isoform in another muscle. Recently it was found that the mRNA coding for the isoform of actin which is the adult type in the cardiac muscle (cardiac actin) is transiently present in the newborn skeletal muscle (60). We have found a converse situation in the heart. In the newborn heart, the skeletal muscle actin mRNA is present in significant amounts, decreasing rapidly with maturation (593,594). The biological significance of these changes and how they are controlled is unknown.
KeywordsMyosin Heavy Chain Actin Gene Globin Gene Chimeric Gene Myogenic Cell
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