Layer-specific expression of multiple cadherins in the developing visual cortex (V1) of the ferret

Cadherins are superfamily of Ca2+-dependent transmembrane glycoproteins with more than 100 members. They play a role in a wide variety of developmental mechanisms, including cell proliferation, cell differentiation, cell-cell recognition, neurite outgrowth and synaptogenesis. We cloned 16 novel members of the classic cadherin and delta-protocadherin subgroups from ferret brain. Their expression patterns were investigated by in situ hybridization in the developing primary visual cortex (V1) of the ferret. Fifteen out of the 16 cadherins are expressed in a spatiotemporally restricted fashion throughout development. Each layer of V1 can be characterized by the combinatorial expression of a subset of cadherins at any given developmental stage. A few cadherins are expressed by subsets of neurons in specific layers or by neurons dispersed throughout all cortical layers. Generally, the expression of protocadherins is more widespread, whereas that of classic cadherins is more restricted to specific layers. At the V1/V2 boundary, changes in layer-specific cadherin expression are observed. In conclusion, our results suggest that cadherins provide a code of potentially adhesive cues for layer formation in ferret V1. The persistence of expression in the adult suggests a functional role also in the mature cortex.