Differential expression,alternative splicing,and adhesive properties of the zebrafish δ1-protocadherins

Protocadherins comprise the largest family within the cadherin superfamily of cell surface receptors. Here, we characterize the δ1-protocadherin subfamily during the development of the zebrafish nervous system. In zebrafish, there are five δ1-protocadherins: pcdh1a, pcdh1b, pcdh7a, pcdh7b, and pcdh9. Each protocadherin gene is highly homologous to its human ortholog. While the expression pattern in the developing CNS is similar for each δ1-protocadherin, with labeling observed in all major subdivisions, the detailed patterns are distinct. In addition, we provide evidence for alternative splicing of the pcdh7b and pcdh9 genes, resulting in variation in their respective cytoplasmic domains. As protocadherins are widely regarded to act as cell adhesion molecules, we used in vitro assays of δ1-pcdh ectodomains to directly test their adhesive properties. We found no evidence for calcium-dependent, homophilic adhesion, contrasting sharply with the behavior of classical cadherins.