Histone Changes during Chromatin Remodeling in Embryogenesis

Variation in chromatin structure, both among cells of different types and within a given cell, is apparent from microscopic and enzymatic analysis (Spadafora et al. 1976; Keichline and Wassermann 1977). This diversity in chromatin structure is generated as development proceeds (Mahowald 1968) and may be related to the functional diversification of chromatin leading to cell differentiation. Histones, as major determinants of chromatin structure, are likely to be involved in some way with this diversification of chromatin structure. Moreover, the great affinity of histones for DNA would seem to make these proteins suitable for long-term maintenance of such diversity. Until recently, however, histones have been considered to be nonspecific structural elements because of evidence that they are few in number and vary little among different tissues.