Cell proliferation in developing human jejunum.

Cell proliferation of the developing human jejunum was investigated by radioautography using organ culture. The sites of [3H]-thymidine uptake were localized in the epithelium, the mesenchyme and the muscularis externa of fetal human small intestinal explants from 8 to 18 weeks of gestation. Proliferating cells were abundant and scattered throughout the stratified epithelium before the appearance of villi. Many nuclei in the mesenchyme and the muscular layer were labeled. With the villi formation and the simplification of the epithelium, there was a confinement of the proliferating zone in the intervillus areas and developing crypts. The quantitation of proliferating cells showed a labeling index at its highest value between 8 and 10 weeks of gestation decreasing gradually up to 18 weeks of gestation at the epithelial and mesenchymal level. In the muscularis externa, the labeling remained more or less constant between 11 and 18 weeks of gestation. The organ culture of intestinal explants for 5 days did not modify epithelial cell proliferation. The present investigation provides for the first time basic quantitative data regarding cell proliferation in the developing human jejunum.