Evidence of a G 1regulation of circadian proliferation in mouse methylcholanthrene-induced sarcomas

Abstract

In two methylcholanthrene induced sarcomas of C 57BL male mice presenting a circadian proliferation (peak of mitoses at noon and peak of labelling indices between midnight and 4 a.m.), the authors performed per cent labelled mitosis curves every 6th hr during the 8th diurnal period of growth. The G 1 phase showed the most important variation with a significant increase in the groups receiving 3H -thymidine at 2 a.m. The possibility that this periodic variation of G 1 phase regulates the circadian rhythm of cell proliferation is discussed.