DIURNAL-VARIATION IN PROLIFERATIVE COMPARTMENTS AND THEIR RELATION TO CRYPTOGENIC CELLS IN THE MOUSE COLON

The depth of the crypts in mouse descending colon varied diurnally between 26 cells at 2400 h and 38 cells at 1200 h. Cell loss from the colon was greatest immediately before the maximum feces production, at the beginning of the dark period. The labelling index of the colon also changed, from 9% at 2000 h to 16% at 1200 h. The greatest variation in labelling index occurred at the top of the zone of proliferative cells, between the 9th and 18th cell position up the crypt. In this region a synchronized cohort of about 40 cells apparently entered S phase once a day. Although the length of the proliferative zone doubled at 1200 h, that of the non-proliferative zone remained fairly constant all day. The number of cryptogenic cells per crypt was estimated by comparing single and split-dose X-ray survival curves. This gave a mean value of 2 cryptogenic cells per crypt. Crypts rarely regenerated from the base after irradiation. The cryptogenic cells probably lay between cell positions 9 and 18 up the crypt and probably did not function as stem cells in the normal crypt.