Accumulation of histone H1(0) during early Xenopus laevis development.

It is known that a transition in the linker-histone variants takes place within chromatin during early development of Xenopus laevis; a cleavage-type H1 is replaced by the somatic type. Based on cytofluorimetric analysis of the distribution of the embryo cells in the cell cycle, we showed that this previously described transition occurs when significant modifications of the proliferative capacities of the cells occur. Moreover, this analysis allowed us to show that cell proliferation decreases gradually after the gastrula stage of development. This period terminates with the arrest of more than 90% of cells in the G0/G1 phase of the cell cycle at stage 45. We showed that the major accumulation of the differentiation-specific H1 subtype, histone H1(0), occurs at this time. H1(0), first detected in a restricted set of tissues, is then widely expressed during the later development at stage 45. Moreover, the double staining of nuclei isolated from embryo cells, for H1(0) and DNA, allowed us to show that this accumulation of H1(0) is not restricted to arrested cells. The example of the Xenopus early development shows that there may be an adaptation of the type of H1 expressed to the proliferative abilities of cells. This observation may provide insight into the significance of the expression of different H1 subtypes during development.