Quantitative cytochemical study of chromatin during megakaryocyte maturation

Several cytochemical parameters useful for characterizing the functional maturation of megakaryocytes were defined following a quantitative cytochemical investigation carried out on megakaryocytes which had completed the DNA synthesis stage. Variations in the ratio between nuclear DNA and cytoplasmic protein contents showed that, at any ploidy level, several maturation stages were concurrently present. The high variability in the basic protein content of the nucleus and in the Feulgen-DNA distribution area was related to the progressive chromatin condensation during thrombocytopoiesis. In particular, the results concerning the ratio between Feulgen-DNA and basic proteins in the nucleus, even after NaCl extraction of lysine-rich histones, pointed out the strong difference between megakaryocytes undergoing maturation and other proliferating cell populations. The different degree of genome activity within the same ploidy class was expressed by changes in the total DNA/double strand DNA ratio. The parallel trends of the DNA hydrolysis kinetics curves suggested a quite similar organization of chromatin in all the ploidy classes examined.