A novel mutation causing nephronophthisis in the Lewis polycystic kidney rat localises to a conserved RCC1 domain in Nek8

John K McCooke,Justyna E Ozimek-Kulik,Roberto A Barrero,Rudi Appels,Mathew I Bellgard,Grant Morahan,Jacqueline K Phillips,Alice Ding

doi:10.1186/1471-2164-13-393

Abstract

BackgroundNephronophthisis (NPHP) as a cause of cystic kidney disease is the most common genetic cause of progressive renal failure in children and young adults. NPHP is characterized by abnormal and/or loss of function of proteins associated with primary cilia. Previously, we characterized an autosomal recessive phenotype of cystic kidney disease in the Lewis Polycystic Kidney (LPK) rat.ResultsIn this study, quantitative trait locus analysis was used to define a ~1.6Mbp region on rat chromosome 10q25 harbouring the lpk mutation. Targeted genome capture and next-generation sequencing of this region identified a non-synonymous mutation R650C in the NIMA (never in mitosis gene a)- related kinase 8 ( Nek8) gene. This is a novel Nek8 mutation that occurs within the regulator of chromosome condensation 1 (RCC1)-like region of the protein. Specifically, the R650C substitution is located within a G[QRC]LG repeat motif of the predicted seven bladed beta-propeller structure of the RCC1 domain. The rat Nek8 gene is located in a region syntenic to portions of human chromosome 17 and mouse 11. Scanning electron microscopy confirmed abnormally long cilia on LPK kidney epithelial cells, and fluorescence immunohistochemistry for Nek8 protein revealed altered cilia localisation.ConclusionsWhen assessed relative to other Nek8 NPHP mutations, our results indicate the whole propeller structure of the RCC1 domain is important, as the different mutations cause comparable phenotypes. This study establishes the LPK rat as a novel model system for NPHP and further consolidates the link between cystic kidney disease and cilia proteins.

Highlights

Nephronophthisis (NPHP) as a cause of cystic kidney disease is the most common genetic cause of progressive renal failure in children and young adults
Numerous studies have been carried out in humans, zebrafish and rodents [3,4] indicating the important function that cilia and associated proteins play in the pathogenesis of renal cystic diseases [5], including polycystic kidney disease (PKD) [6,7] and nephronophthisis (NPHP) [8] incorporating Merkel Gruber and Joubert Syndromes [9]
The cyst/kidney area ratio quantitative trait locus (QTL) (LPK phenotype) mapped the lpk locus with a logarithm of odds (LOD) score of 50 to the region defined by the markers D10Rat30 and D10Mgh14

Summary

Introduction

Nephronophthisis (NPHP) as a cause of cystic kidney disease is the most common genetic cause of progressive renal failure in children and young adults. Mutation of the Pkhd gene encoding for fibrocystin/polyductin results in autosomal recessive (AR) PKD This gene was first identified in the PCK rat [13] and encodes an integral structural component of both the cilia and basal body associated with the centrosome [14,15]. Another example relates to polycystin-1 and -2 expression, both of which have been shown to regulate the JAK-Stat pathway, which in turn controls cell cycle arrest in G0 and G1 [16]. Wnt signaling has been shown to have oncogenic activity, becoming deregulated in certain types of cancers [18,19] and polycystin-1 regulates genes responsive to Wnt signaling [20], inhibiting proliferation and maintaining normal microtubular structures

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