Contact and adhesive specificities in the associations, migrations, and targeting of cells and axons

Abstract

What determines whether cells remain in one place, retaining their associations with their neighbors, or dissociate from these associations and move elsewhere? And, if they move, what determines where they go, where and when they stop, and whether or not they associate with like or unlike cells? These questions arise about many events during development, especially but not exclusively the development of the nervous system. The same questions arise when considering normal physiological processes, such as lymphocyte traffic, wound healing, and hemostasis, and pathologies such as invasion and metastasis, thrombosis, and inflammation. All these processes involve alterations in cell associations, many involve cellular (or axonal) migration, and all must be conducted with appropriate specificity to ensure proper development and function of the organism. Yn recent years there have been major advances in deciphering the molecular bases for the cell adhesion events underlying these biological phenomena. Perhaps it is not surprising that there are many different adhesive molecules involved; at times there appears to be a bewildering variety. However, common themes are emerging, and many of the molecules fall into families whose members appear in the different processes performing similar roles. This means that insights obtained in one system can be applied in others, and this cross fertilization among disciplines is proving very fruitful. In this review we will discuss current ideas concerning the roles of cell adhesion molecules and cell interactions, both in development and in several physiological and pathological processes, attempting to highlight the general features and commonalities and presenting working hypotheses.