CADHERINS AND THE FORMATION OF NEURAL CIRCUITRY IN THE VERTEBRATE CNS

Cadherins are a family of calcium-dependent morphoregulatory molecules mediating cell-cell adhesion. More than a dozen cadherin subtypes are known to be expressed in the developing and mature CNS. Each of these subtypes shows a restricted and distinct expression pattern that diff ers from that of the other cadherins. During the formation of fiber tr acts and neural circuits, each cadherin is expressed by a subset of ne urite fascicles. The differential expression of cadherins provides a m olecular code for the high degree of specificity and selectivity in ne ural circuit formation. This code may be a combinatorial one, since th e expression of cadherins shows partial overlap. The expression data a nd experimental results available at present suggest a role for cadher ins in aspects of axon outgrowth, axon navigation, axon fasciculation, axonal target recognition, and, finally, in synaptogenesis. However, the precise role of cadherins in some of these processes and their fun ctional relationship to other molecules involved in neurite outgrowth remains to be experimentally established.