THE RELATIONSHIPS AMONG STEM-CELLS, CRYPTS, AND VILLI IN THE SMALL-INTESTINE OF MICE AS DETERMINED BY MUTATION TAGGING

The number of stem cells that maintain a crypt of the small intestine is uncertain, Although the number of stem cells per crypt had been tho ught to be 10-20, current estimates indicate a much smaller number, po ssibly 1 stem cell per crypt. We report here that in SWR and C57BL/6 X SWR F-1 mice, the results of mutation tagging are inconsistent with t he existence of more than one stem cell per crypt. Mutations at the Dl b-1 locus mark the progeny of a single epithelial stem cell in the sma ll intestine and reveal the size of the mutant clone. The epithelial c ells are produced in the crypts and migrate up the villi to be sloughe d off at the tip so that a mutant clone takes the form of a ribbon on the villus. Because the size of the mutant clones must be inversely pr oportional to the number of stem cells contributing to the villus, thi s provides a means of counting the stem cells (ethylnitrosourea was us ed to induce mutations in the intestine). In the duodenum the ribbons average 0.099 +/- 0.004 villus circumferences, indicating that there a re 1/0.099 = 10.2 stem cells per villus, Because there are 10.5 +/- 0. 67 crypts/villus, the estimate gives 10.2/10.5 = 0.97 +/- 0.1 stem cel ls/crypt. Because each crypt must have at least one stem cell, the vas t majority can have only one stem cell and very few may have two or mo re. (C) 1996 Wiley-Liss, Inc.