Cell Differentiation: Some Aspects of the Problem

Abstract

Differentiation of a group of cells can be directed experimentally by regulating the availability of the substrates and cofactors necessary for protein synthesis. Several lines of evidence indicate that, during development, there is a temporal sequence of activity of groups of genes that play a role in the differentiation of the various kinds of cells. It is possible that this activity may be expressed by the production of specific ribonucleic acid molecules by DNA, or perhaps only by derepression or activation, so that some of the genes of the chromosomal DNA are capable of forming specific RNA. Whether these derepressed or activated genes will go ahead and synthesize proteins that will specify what kind of cell will result from differentiation may depend upon the availability of substrates and energy for protein synthesis, and upon the level of activity of various components of the protein-synthesizing machinery. If the levels of substrates and cofactors needed for protein synthesis are too low at a time when the groups of genes that code for the synthesis of proteins of one cell type are capable of acting, then the synthesis of these specific proteins will not take place and the cells will not differentiate into cells of that type. If the metabolic level becomes optimal in these cells later, when other group of genes are active, then these other genes will direct the synthesis of proteins that will specify differentiation into cells of another kind.