Nonsense-associated alternative splicing as a putative reno-protective mechanism in Pkhd1cyli/Pkhd1cyli mutant mice

Autosomal recessive polycystic kidney disease (ARPKD) is a hereditary hepato-renal fibrocystic disorder and a significant genetic cause of childhood morbidity and mortality. Mutations in the Polycystic Kidney and Hepatic Disease 1 (PKHD1) gene cause all typical forms of ARPKD. Several mouse strains carrying diverse genetically engineered disruptions in the orthologous Pkhd1 gene have been generated. The current study describes a novel spontaneous mouse recessive mutation causing a cystic liver phenotype resembling the hepato-biliary disease characteristic of human ARPKD. Here we describe mapping of the cystic liver mutation to the Pkhd1 interval on Chromosome 1 and identification of a frameshift mutation within Pkhd1 exon 48 predicted to result in premature translation termination. Mice homozygous for the new mutation, symbollzed Pkhd1cyli, lack renal pathology, consistent with previously generated Pkhd1 mouse mutants that fail to recapitulate human kidney disease. We have identified a profile of alternatively spliced Pkhd1 renal transcripts that are distinct in normal versus mutant mice. The Pkhd1 transcript profile in mutant kidneys is consistent with predicted outcomes of nonsense-associated alternative splicing (NAS) and nonsense mediated decay (NMD). Overall levels of Pkhd1 transcripts in mutant mouse kidneys were reduced compared to kidneys of normal mice, and Pkhd1 encoded protein in mutant kidneys was undetectable by immunoblotting. We suggest that in Pkhd1cyli/Pkhd1cyli (cyli) mice, mutation-promoted Pkhd1 alternative splicing in the kidney yields transcripts encoding low-abundance protein isoforms lacking exon 48 encoded amino acid sequences that are sufficiently functional so as to attenuate expression of a renal cystic disease phenotype.