Influence of metabolic DNA on determinations of the cell cycle.

Abstract

Abstract. Evidence in favour of labelling of DNA in excess of requirements for mitosis was found in adult organs showing no mitosis (heart muscle and brain), in organs with low mitotic indexes (liver, seminal vesicle) and, more recently, in the small intestine of rodents, in bone formation and in growing roots of Vicia faba. A survey of published data showed higher labelling indexes than would be expected from the data for S, M and tc deducted from labelled mitoses curves. to improve the accuracy of the data needed for a complete assessment the duration of mitosis (M) and the proportion of cells which are no longer in the mitotic cycle in the crypts were determined using Colcemid. the fact that all cells in the villi are derived from the crypts and that there is no cell‐loss in the villi was checked by cell‐counts.The results show that 3040%of the labelled nuclei found in crypts of the jejunum of mice at 1 hr after injection of 3H‐thymidine do not proceed to mitosis.The labelling after the last mitosis is interpreted as formation of the metabolic DNA necessary for the function of the differentiated cells in the villi. There is some evidence that metabolic DNA necessary for the processes of mitosis might be lost