Histogenesis of the mouse jejunal mucosa, with special reference to proliferative cells and absorptive cells.

The histogenesis of the mouse jejunal mucosa and distribution of cells capable of proliferation were studied by scanning and transmission electron microscopy and light microscopic autoradiography using 3H-thymidine. Villous primordia were found to commence their development as mucosal ridges on day 15 of gestation. Individual villi are identifiable on day 16 of gestation. Some villi reach their adult height in the neonate, while the rest gradually become longer during postnatal development. Epithelial cells lining the entire mucosal surface are undifferentiated and proliferative by day 15 of gestation. On day 16 of gestation, cells lose their proliferative capability at the upper part of the high villi, while cells lining the lower part of the villi and intervillous region remain undifferentiated as well as proliferative. As the crypt develops during postnatal development, undifferentiated proliferative cells are restricted in it, coming to reside in the lower two thirds of the crypt by day 28. The fine structural differentiation of absorptive cells starts at the upper part of villi on day 16 of gestation. The apical tubular system develops during the perinatal period. Large vacuoles, many lysosomes and lipid globules appear in suckling mice. The cells show the typical morphology of the absorptive cells by postnatal day 21. Undifferentiated proliferative cells show only little change during development: cytoplasmic organelles increase slightly and small apical granules appear during postnatal development.