Molecular and genetic analysis of a new insertional mutation in the TgN(Imorpk)73Rpw line of mice that causes polycystic kidney disease.

A line of transgenic mice has been generated that contains an insertional mutation causing a phenotype similar to human autosomal recessive polycystic kidney disease. TgN737Rpw homozygotes display a complex phenotype that includes bilateral polycystic kidneys and an unusual liver lesion. The mutant locus was cloned and characterized through use of the transgene as a molecular marker. A deletion of no more than 2.77 kb, and the insertion of 21.0 kb of genomic mouse DNA that stably cointegrated with the transgene, occurred at the integration site. An extended physical analysis of the mutant locus, which included pulsed field gel electrophoresis (PFGE), detected no additional rearrangements beyond the insertion site. A candidate polycystic kidney disease (PKD) gene was identified whose structure and expression is directly associated with the mutant locus. A cDNA derived from this gene predicted a peptide containing multiple repeats of a degenerate 34-amino acid motif that defines members of the tetratricopeptide repeat (TPR) gene family, which are often involved in cell cycle control. The TgN737RpwcDNA hybridizes to multiple transcripts during embryogenesis and in all wild-type adult tissues examined, and a cDNA isolated from embryonic day 14.5 may represent an alternatively-spliced form of the TgN737Rpw gene. Physical mapping data and the gene's expression pattern suggest that the mutant phenotype in TgN73 7Rpw mice is due to the disruption of a single, ubiquitously-expressed gene that functions during embryonic development and into adulthood. The TgN737Rpw mutation is the first candidate gene accessed at the molecular level in any PKD model, and does not appear to be allelic with existing mouse models of PKD. The TgN737Rpw gene also represents the first in vivo TPR mutation in vertebrates. Moreover, the identification of the homologous human gene will permit a thorough molecular study of whether this gene is directly associated with any of the various forms of PKD in humans.