Deoxyribonucleic acid synthesis, mitosis, and skeletal muscle differentiation

Abstract

In the past, it was generally thought that processes of differentiation and proliferation in eukaryotic cells were antagonistic, the implication being that somehow the two processes cannot go on simultaneously within the same cell. There are, however, many examples of synthesis of deoxyribonucleic acid and of specialized cell proteins occurring simultaneously in the same cell (1-5). It has become clear in recent years that it would be more accurate to say that there are several differentiating systems in which special relationships exist between the events leading to overt differentiation and cell proliferation. Some of the better studied examples are in erythroid differentiation, where a programmed sequence of cell division occurs (6-9); in formation of tubular gland cells, in which division is required for the formation and subsequent synthesis of ovalbumin in the chick oviduct (10, 11); in viral transformation of cells, where cell division is required to establish this state (12-15); in the differentiation of mammary gland epithelium, where cell division must occur in the presence of hydrocortisone in order for prolactin to stimulate milk protein synthesis (16, 17); and in the differentiation of skeletal muscle cells, where cells synthesizing contractile proteins do not divide (18, 19). For several years we have been exploring the relationship of cell proliferation and differentiation in skeletal muscle cells differentiating in vitro. We describe this relationship and relate some of our general conclusions about deoxyribonucleic acid synthesis in differentiating myogenic cells. DISCUSSION