CELL-CELL ADHESION AMONG EMBRYONIC CELLS

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During embryonic development, cells are brought together by mechanochemical means resulting in embryonic induction. This milieu-dependent differentiation gives rise in turn to tissues and organs. The long term goal of this proposal is to analyze how the cellular interactions of embryonic induction lead to morphogenesis in normal development and how derangements of these interactions give rise to developmental defects. Because of the central role of cell contact in these events, our approach has been to identify and chemically define the structure and activities of cell adhesion molecules (CAMs). Several CAMS have now been identified and characterized in detail and cDNA probes for these molecules have been defined. Immunohistochemical studies show that CAMs are expressed at sites of embryonic induction as well as at salient stages of tissue and organ formation. Early in development, this expression follows a definite set of rules which are general to a great variety of tissues. These observations suggest that locale-specific regulation of defined molecules mediates the pivotal process of cell adhesion in morphogenesis and histogenesis. Two main complementary approaches will be used to extend and deepen this conclusion. First, detailed localization of CAMs in normally developing tissues will be carried out by immunological and gene probe techniques and correlated with known developmental interactions and processes. Second, the function of CAMs will be perturbed at different stages of development and the biochemical and histological changes caused by the perturbations will be analyzed in light of the localization studies. Specifically we will: (1) make a detailed analysis of CAM expression in liver, kidney, limb, and lung and in optic and otic placodes (2) use antibodies to perturb CAM functions in organ and cell cultures of these tissues and in the intact embryo at stages of development when inductive and morphogenetic events are known to occur (3) continue studies to detect, isolate, and characterize new CAMs (4) determine the role of CAMs in the formation of neuronal connections in the cerebellum and the retinotectal system and (5) utilize cultures of skin cells producing appendages such as feathers as well as nervous tissue explants to define factors that are involved in the control of CAM expression.