Identification of gammaA-like protocadherin expressed during chick development

The protocadherins are calcium-dependent cell adhesion molecules of the cadherin superfamily that have been described in numerous species. Although less well characterized than classical cadherins, the protocadherins are also thought to facilitate critical cell-cell interactions during embryonic development. We have cloned a novel protocadherin from the embryonic chick utilizing a monoclonal antibody produced against a peanut agglutinin-binding fraction of cultured chick limb tissue to screen a lambdaZAP cDNA expression library from the stage 25 limb. A 2.8 kb cDNA clone was obtained that encoded multiple cadherin-like ectodomains. Northern blotting revealed a single 4.6 kb RNA transcript that was highly enriched in the stage 43 chick brain. Utilization of 3' Rapid amplification of cDNA ends (RACE) identified the entire 2.4 kb reading frame. The chick protocadherin contained five cadherin-like extracellular repeats and a highly conserved cytoplasmic domain. Amino acid alignment of the extracellular domains revealed marked identity to the human gammaA protocadherin subfamily. In situ hybridization showed low levels of mRNA localization in several developing chick tissues, but stronger expression in the neural tube and dorsal root ganglia at stage 27. In the stage 43 chick brain, protocadherin mRNA was noted in discrete regions, particularly within the developing optic lobe. As for protocadherins described in other species, these results suggest that this novel gammaA-like protocadherin may also play a role in chick neural development.