Patterns of proliferation in the hypophysis of the mouse embryo

Summary

The process of proliferation and growth in the neurohypophysis and adenohypophysis of the mouse embryo was studied by means of tritiated thymidine autoradiography. the percent of cells labeled (labelings index, LI) was determined in embryos ranging from 9 through 16 days of gestation one hour after an intraperitoneal injection of ³H-thymidine in the mother. The infundibular region of the diencephalon showed an early abd dramatic decrease in proliferation between the tenth and eleventh days of gestation, in contrast to the hypophyseal (Rathke's) pouch which showed a consistently high level of activity during these stages. During days 12–16 the infundibulum was very sparsely labeled but continued to exhibit a low rate of mitotic activity as it developed into the neurohypophysis. The dorsal wall of the hypophyseal pouch which represents the intermediate lobe of the hypophysis was well labeled, and even at 16 days of gestation its labeling index was approximately 25%. The major portion of the hypophyseal pouch representing the pars distalis showed a highly active proliferation, particularly in its lateral regions at early stages, but by 13 and 14 days of gestation many of the cells failed to incorporate the label as they became grouped into loose clusters. By 15 days' gestation much of the hypophyseal pouch, particularly its ventral and lateral portions, became highly vascularized, and the majority of its labeled nuclei represented those of endothelial cells.