Formation and loss of DNA in intestinal epithelium.

The hypothesis that all nuclei containing labelled DNA in the jejunum of adult mice divide before migrating into the villi and that the amount of labelled DNA is constant during the passage of cells through the villi was tested experimentally. Mice were killed 40 min, 12, 18, 24, 30 and 36 h after a single intraperitoneal injection of [H]thymidine. Grain counts in stripping film autoradiographs showed (i) considerably higher grain counts in the villi 24 h after injection than expected from those in the crypts at 40 min, and (ii) a loss of 32 % of the grain count during passage of the cells through the villi. Consideration of various factors which might influence the grain counts show that the findings have to be accepted as correct. It is suggested that a considerable proportion of the nuclei labelled in the crypts migrate into the villi without subsequent division and that labelled DNA is lost during passage through the villi. The hypothesis of formation of metabolic DNA during differentiation and loss during function provides an explanation of the findings.