Differentiation, Growth, and Maturation of Neurons
The control of cell differentiation in eukaryotes is exerted at many levels: DNA replication, transcription, and translation, activation of enzymes, and control of membrane permeability by hormones or other intercellular transmitters. Transcriptional control is particularly important in eukaryotes because of the presence of the cytoplasm, which can store and sequestrate factors that control gene expression, and because of the presence in eukaryote chromatin of some proteins that inhibit transcription and others that activate it. As Britten and Davidson (1969, 1971) have recognized, the histones produce a nonspecific, general repression of transcription, whereas differential gene action consists largely of counteracting this repression by means of activators that are specific with respect to their time of action and with respect to the gene loci that they activate. These activators may be hormone-protein complexes and cytoplasmic factors that enter the nucleus and become bound to acidic, nonhistone proteins in the chromosomes (Davidson and Britten, 1973).
KeywordsNerve Fiber Peripheral Nerve Sciatic Nerve Schwann Cell Chick Embryo
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