| Abstract: | We have used immunofluorescent staining of sea urchin embryos to study how histone H1 alpha is distributed among progeny cells formed after the cessation of its synthesis. Our results are consistent with H1 alpha being distributed to both daughter cells at mitosis, resulting in it being most concentrated in cells that stop dividing shortly after H1 alpha synthesis ends, while cells that continue to divide dilute their H1 alpha content in proportion to the number of cell divisions. This rules out our earlier suggestion that H1 alpha becomes segregated in dividing cells. In addition, our results show that most dividing cells of the 3-day embryo contain predominantly H1 beta and H1 gamma. Since these subtypes are known not to undergo phosphorylation, this finding has implications regarding the roles of H1 phosphorylation in the cell cycle. |
