Origin, differentiation and renewal of the four main epithelial cell types in the mouse small intestine III. Entero‐endocrine cells

Abstract

The origin, differentiation and renewal of entero‐endocrine cells was examined in the duodenum, jejunum and ileum of the mouse using light and electron microscopic radioautography after a single injection or continuous infusion of 3 H‐thymidine. When s‐collidine buffered glutaraldehyde was used for fixation prior to electron microscopic study, all granules in all entero‐endocrine cells were spheroidal and, therefore, their shape could not be used to classify the cells into subgroups, as done after fixation in phosphate buffered aldehyde. Thus, the cells were all considered as belonging in a single family. In the light microscope, mitosis is not observed in the entero‐endocrine cells identified by iron hematoxylin staining. However, under the electron microscope, a few cells that contain a small number of characteristic granules, some filament bundles and many free ribosomes are in division or are labeled one hour after an injection of 3 H‐thymidine. These cells are interpreted as young entero‐endocrine cells. They are located in the crypt base. They resemble crypt‐base columnar cells and are, therefore, suspected of arising from them. Differentiation may be examined by following the fate of the young enteroendocrine cells which are labeled by 3 H‐thymidine. Within the crypts, these cells acquire a gradually increasing number of granules while losing the ability to divide. The few granules initially present usually have a particulate content and may include a small dense core; but, as differentiation proceeds and granules accumulate, their content is mostly dense and homogeneous. The differentiation of precursor cells into mature entero‐endocrine cells takes about two days. Meanwhile, in the same manner as columnar and mucous cells, enteroendocrine cells migrate up the crypt, reach the villus and are lost at the extrusion zone. The turnover time of entero‐endocrine cells is estimated to be 3.9 days in duodenum and 4.0 days in jejunum.