NCAM and its polysialic acid moiety: a mechanism for pull/push regulation of cell interactions during development?

Many cell adhesion molecules have a distinct pattern of expression and well-defined role in cell-cell recognition. In contrast, NCAM is broadly expressed and perturbations of its function affect many diverse aspects of embryonic development. Evidence has been obtained suggesting that the molecule and its polysialic acid moiety serve not only to contribute to specific interactions, but also to regulate overall cell-cell apposition. In this latter mode, the molecule can have both a positive and a negative effect on a wide variety of contact-dependent cellular events.