DIFFERENTIATION OF THE CHORIONIC EPITHELIUM OF CHICK-EMBRYOS MAINTAINED IN SHELL-LESS CULTURE

In order to determine whether the chorionic epithelium (CE) of the chorioallantoic membrane (CAM) of chick embryos maintained in shell-less culture might be suitable for studies of calcium translocation and/or tissue grafting, membranes from 10- to 18-day embryos were studied histologically using Nomarski differential interference optics on living, unfixed tissue and ultrastructurally using scanning and transmission electron microscopy. Differentiation of the CAM of cultured embryos appeared similar to thatin ovo. At 10 days, an electron-lucent squamous cell layer covered much of the CE. Intraepithelial capillaries were separated from the chorionic surface by a relatively thick (>5-μm) cytoplasmic layer. By 12 days, dense, vacuolated, apparently degenerating cells covered much of the CE. At later stages (14 to 16 days), degenerating cells were seen infrequently and most capillaries were covered by thin (<0.2-μm) cytoplasmic processes. By 18 days cultured CAM no longer appeared normal, but demonstrated local sites of squamous metaplasia. Villus-cavity and capillary-covering cells were observed in culture by 10 to 14 days of total incubation. These studies indicate that the presence and active transport of large amounts of calcium from the eggshell are unnecessary for normal differentiation of the CAM. Thinning of the cytoplasmic barrier overlying the chorionic capillaries and progressive rounding of endothelial cell nuclei indicate that vascularization of the CAM in culture follows a course similar to thatin ovo. © 1979 Academic Press, Inc. All rights reserved.