Identification of porcine polycystic kidney disease 1 ( PKD1) gene: Molecular cloning, expression profile, and implication in disease model

Abstract

The polycystic kidney disease 1 ( PKD1) gene, which accounts for ~ 85% of human autosomal dominant polycystic kidney disease (ADPKD) cases, has been extensively studied in human and mouse. Much information about the pathogenesis of and treatments for ADPKD has been gained from the use of mouse models. However, because mouse models pose some limitations, further studies in other model systems are needed to investigate the biological basis of ADPKD. The pig is regarded as an important biomedical model. Thus, we isolated a pig PKD1 homolog and characterized its cDNA sequence, genomic structure, expression profile, alternative splicing, methylation status, protein characteristics, and immunohistochemical features in both neonatal and adult pigs. The pig PKD1 cDNA is 14,209 bp long and encodes a 4305-residue polypeptide. The genomic sequence of PKD1 is ~ 50 kb with 46 exons. An alternative splice acceptor site was identified in intron 9. PKD1 is expressed in all tissues tested in both neonatal and adult pigs and exhibits a developmentally regulated expression pattern. Western blotting revealed that the molecular mass of polycystin-1 is ~ 460 kDa, but its expression level is relatively low. Immunohistochemical study of the kidneys shows that polycystin-1 is mainly expressed in the tubular epithelia. Bisulfite methylation analysis of CpG islands in the promoter region does not show a direct correlation between methylation status and expression level among different tissues/cells. The cloning and characterization of pig PKD1 indicates that the pig and human genes are highly similar in length of genomic and cDNA sequences, genomic structure and context, expression patterns, conserved transcription factor binding sites, and the molecular mass of the encoded polycystin-1. These data support our current understanding of PKD1, and suggest that the pig is an ideal candidate for development of an ADPKD disease model.