Prenatal differentiation of bovine oviductal epithelium: an electron microscopic study

In this study, we investigated the ultrastructural changes during the prenatal differentiation of oviductal epithelium in 16 bovine embryos and fetuses from CRL of 18.0 cm to a CRL of 94.0 cm. Ciliated and secretory cells of bovine uterine tube, a derivative of the Müllerian duct, differentiate to distinct development stages in the prenatal period. The typical cellular pattern, which is generally characteristic for the adult bovine oviduct, is also obtained during fetal life. In the early stages (CRL 18.0/20.4 cm), the bovine oviductal epithelium appears mostly undifferentiated. The epithelial cells show only a few mitochondria, some cisternae of rough endoplasmic reticulum (rER) and a small Golgi-complex. Most of the cytoplasm is filled with a large amount of glycogen, which decreases during later development. Interspersed between the undifferentiated epithelial cells, a few cells undergoing ciliogenesis can be observed. Ciliogenesis increased significantly during the later prenatal developmental stages. At a CRL of 55.0 cm, ciliated cells appear fully differentiated with mature cells covering their luminal surface. Formation of cilia usually use the acentriolar pathway. Fibrous granules occurred initially in association with the Golgi-apparatus and r(ER) in the supranuclear cytoplasm. Fibrous granules later fuse with deuterosomes and give rise to procentrioles, which are translocated to the luminal plasma membrane. There they become arranged in a line just beneath the apical cell membrane and further differentiate to basal bodies from which the formation of cilia and striated rootlets take place. Clear signs of differentiation of secretory cells were first seen in our material in fetuses with a CRL of 51.0 cm and 64.0 cm. These cells contain a well developed rER and Golgi-apparatus with dilated cisterns. In the supranuclear cytoplasm, the number of secretory granules continuously increases during later development and the cells adapt to the morphology of mature secretory cells at the CRL 94.0 cm.