Ontogenetic expression of cell adhesion molecules: L-CAM is found in epithelia derived from the three primary germ layers.

Immunofluorescence techniques using specific antibodies against the liver cell adhesion molecule, L-CAM, were used to explore the appearance of L-CAM during early embryogenesis and organogenesis, as well as in adult tissue. Immunoblots of L-CAM from embryonic and adult organs indicated that molecules detected in each tissue were L-CAM, and that the antibodies were not simply detecting cross-reacting molecules. L-CAM was found in low levels on pregastrulation embryos. During gastrulation, the molecule remained present on ectoderm but was not detected on mesodermal and definitive endodermal cells. During neurulation, L-CAM disappeared from the neural ectoderm, in which staining for the neural cell adhesion molecule, N-CAM, had previously been shown to increase markedly. During organogenesis, L-CAM appeared in all endodermal structures, in ectoderm other than neural derivatives, in placodes, in extraembryonic ectoderm and endoderm, and in some mesodermal structures such as Wolffian ducts, oviduct, and kidney epithelium. Other mesodermal derivatives were not stained and the molecule was not detected in hemangioblastic areas of the lateral plate mesoderm nor in splanchnopleural derivatives such as spleen, adrenal glands, and gonads. During embryonic induction, for example, neurulation and in early kidney development, changes in L-CAM distribution were correlated with both locations and times of induction events. Analysis of distribution in the adult revealed that L-CAM was present in the stratum germinativum of the skin, in endodermally derived epithelia, in the female reproductive tract, and in the kidneys. In several fully differentiated glandular organs, L-CAM staining was restricted to basal or apical parts of the cell surface. When correlated with previous results obtained for N-CAM, these findings support the idea that local cell surface modulation of a small number of cell adhesion molecules may regulate other primary processes of development to yield specific patterns, both in early development and in organogenesis. Reflections of these patterns remain in adult life.