Cystin, a novel cilia-associated protein, is disrupted in the cpk mouse model of polycystic kidney disease
Xiaoying Hou, … , David R. Beier, Lisa M. Guay-Woodford
Xiaoying Hou, … , David R. Beier, Lisa M. Guay-Woodford
Published February 15, 2002
Citation Information: J Clin Invest. 2002;109(4):533-540. https://doi.org/10.1172/JCI14099.
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Article Genetics

Cystin, a novel cilia-associated protein, is disrupted in the cpk mouse model of polycystic kidney disease

Abstract

The congenital polycystic kidney (cpk) mutation is the most extensively characterized mouse model of polycystic kidney disease (PKD). The renal cystic disease is fully expressed in homozygotes and is strikingly similar to human autosomal recessive PKD (ARPKD), whereas genetic background modulates the penetrance of the corresponding defect in the developing biliary tree. We now describe the positional cloning, mutation analysis, and expression of a novel gene that is disrupted in cpk mice. The cpk gene is expressed primarily in the kidney and liver and encodes a hydrophilic, 145–amino acid protein, which we term cystin. When expressed exogenously in polarized renal epithelial cells, cystin is detected in cilia, and its expression overlaps with polaris, another PKD-related protein. We therefore propose that the single epithelial cilium is important in the functional differentiation of polarized epithelia and that ciliary dysfunction underlies the PKD phenotype in cpk mice.

Authors

Xiaoying Hou, Michal Mrug, Bradley K. Yoder, Elliot J. Lefkowitz, Gabriel Kremmidiotis, Peter D’Eustachio, David R. Beier, Lisa M. Guay-Woodford

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Organization of the cpk genomic sequence and identification of the cpk m...
Organization of the cpk genomic sequence and identification of the cpk mutation. (a) Alignment of the cpk cDNA, the UniGene consensus sequences, and the BAC genomic sequence demonstrated that the cpk gene is encoded in five exons spanning 14.4 kb of genomic DNA. The first nucleotide of the cDNA corresponds to the first nucleotide of exon 1, which spans 1,184 bp and is the largest of the five exons. This exon contains an ATG start site that lies within a Kozak consensus sequence (CGCGCCatgG). The 435-bp ORF extends into exon 3. Exons 4 and 5 are apparently untranslated, and a putative cryptic splice site (gaacagCTG) within exon 5 appears to account for the 1,856-bp and 1,786-bp (gray box) splice variants. An atypical polyadenylation signal (ATTAAA) lies 22-nt upstream of the poly(A+) tail. Of note, the microsatellite marker, D12Mit12, lies within intron 1 of the cpk gene. (b) PCR amplification and direct sequence analysis identified tandem 12-bp and 19-bp deletions in exon 1 of the cpk gene. The comparative sequence is indicated in bold text. The resulting frameshift truncates the predicted protein. The position of the PCR primers is identified by arrows. The putative Kozak sequence is underlined and italicized. (c) Primers flanking the tandem deletion in the cpk mutant allele amplify a 351-bp product from wild-type (B6 and D2) DNA, a 320-bp product from B6-cpk/cpk DNA, and both bands from B6-+/cpk and F1+/cpk heterozygotes. In the key F2cpk/cpk recombinants (R1–R5), only the 320-bp mutant allele was amplified.