Cloning and characterization of zebrafish protocadherin-17.

Protocadherins constitute the largest subgroup within the cadherin superfamily of cell surface molecules. In this study, we report the molecular cloning and expression analysis of the non-clustered protocadherin-17 (pcdh17) in the embryonic zebrafish nervous system. The zebrafish Pcdh17 protein is highly conserved, exhibiting 73% sequence homology with the human protein. The zebrafish pcdh17 gene consists of four exons spread over 150 kb, and this organization is highly conserved throughout vertebrates. Pcdh17 message is first detectable by 6 h postfertilization in the developing embryo, and the expression is maintained throughout development. Zebrafish embryos express pcdh17 in all of the major subdivisions of the central nervous system, including the telencephalon, diencephalon, mesencephalon, and rhombencephalon. Analysis of the genomic sequence upstream of pcdh17 in several species reveals a pattern of paired CpG islands. While the CpG islands in zebrafish are further upstream than in other teleosts, alignment of the identified sequences reveals a high degree of conservation, suggesting that the sequences may be important for the regulation of pcdh17 expression.