[Some cytochemical characteristics of the chromatin in the erythrocytes of Xenopus laevis Daud].

Abstract

The Xenopus laevis Daud. genome offers a stimulating model of a chromatin (Davidson et al., 1975) in which a high ratio of repetitious DNA sequences has been recorded (45% of total genome according to Davidson et al., 1975). We have studied cytochemically this model "in situ", on the erythrocytes of air-dried smears of peripheral blood. The cells, which are non-dividing and not engaged in DNA reduplication, constitute almost hypothetically a homogeneous class constantly in G1 phase of the cellular cycle. Our methods are: a) analysis on the curves of Feulgen hydrolysis kinetics to attempt to find the depurination and depolymerisation patterns of DNA according to Andersson et al. (1975); b) determination of the DNA resistence ratio to chemical denaturation with a quantitative relative microdensitometric determination of methyl-green staining, according to Scott (1967) specific technical conditions. For comparison, qualitative and preliminarly subjective control determinations have been made with acridine-orange in correspondent denaturation conditions. Both the a) and b) methods have been performed with and without previous HCl dehystonisation and with and without formaldehyde pretreatment. The results with the a) and b) methods have not yet been theoretically compared and the possibility of an approach to this correlation is discussed here as a tool for a possible cytochemical quantitative measure of the nuclear fraction of repetitious DNA "in situ".