Microphotometry of rat liver nucleoproteins during the cell cycle, and comparison of diploid nuclei in the G2 period with tetraploid nuclei

Abstract

Summary The following facts were established with a microphotometric investigation of isolated nucleic from rat liver in different stages of the cell cycle. During the mitotic wave occurring in the liver of newborn animals after injection of casein it was found that the naphtol yellow S (NYS) protein content of the nuclei increases about 30% during the G₁-period. A second increase of around 70% was established during the S-phase whereas no increase could be observed during the G₂-phase. An indication for the existence of a “crital protein mass” of the nuclei before the onset of the S-phase could be observed. The protein content of diploid nuclei in the G₁-phase of adult animals is about 50% higher than in newborns. This makes it probable that there is no significant difference in the NYS-protein content of diploid nuclei in the G₂-period and tetraploid nuclei of adult rats. No differences were observed between diploid nuclei in the G₂-period of newborn rats and tetraploid nuclei of adult rats in their Fastgreen histon, RNA and SH plus SS content. The only criterion to distinguish between G₂ nuclei and tetraploid nuclei seems to be the number of nucleoti, but this is rather unreliable.