Cadherins as regulators for the emergence of neural nets from embryonic divisions

Cadherins are a large family of cell adhesion molecules that are expressed in a spatially restricted fashion during vertebrate CNS development. Each cadherin shows a characteristic expression pattern that differs from that of other cadherins. Early in development, the cadherin expression domains relate to the neuromeric organization of the vertebrate CNS. Later, as functional structures (brain nuclei, cortical regions, fiber tracts and synapses) emerge, the expression patterns of each cadherin become restricted to subsets of these structures that form parts of specific neural nets. Cadherins thus represent a system of potentially adhesive cues that play a role in the emergence of neural nets from embryonic CNS divisions. We review descriptive and experimental evidence for such a role of cadherins in CNS development. It is argued that descriptive studies (i.e., the mapping of gene expression) and functional studies (i.e., experimental manipulation of gene expression) are equally important for generating specific and firm ideas on the function of genes in brain development.