Cell Cycle Dependence of Erythroid Maturation
Although the term was only introduced by Holtzer in 1964 (Holtzer, 1964), the concept of the quantal cell cycle in differentiation has been in existence for a long time. It is used to describe a cell division which is necessary for a phenotypic change to occur in a cell lineage and has been particularly studied by Holtzer’s group and others in myogenesis. It does not necessarily imply that the two daughter cells are different from each other, but in some models one daughter cell is identical with the parent and the other is not. It has, however, become clear that, while quantal cell division may be implicated in the determination of some phenotypic characteristics, they are not mandatory for all, for there are some well defined exceptions. Among the most striking are experiments in which nuclei have been injected into oocytes (De Robertis et al, 1977; Gurdon et al, 1978). These have shown quite conclusively that inactive genes in the injected nuclei can be activated without any nuclear division or DNA synthesis. It is possible that oocytes are special but the inescapable implication is that cell division is not essential for all kinds of gene activation. In this paper we discuss evidence that a round of DNA synthesis is mandatory for the final stages of erythroid maturation (in many respects analogous to the final stages of muscle differentiation).
KeywordsWild Type Cell Erythroid Differentiation Permissive Temperature Haemoglobin Synthesis Globin mRNA
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