The Oak Ridge Polycystic Kidney mouse: modeling ciliopathies of mice and men

Abstract

The Oak Ridge Polycystic Kidney (ORPK) mouse was described nearly 14 years ago as a model for human recessive polycystic kidney disease. The ORPK mouse arose through integration of a transgene into an intron of the Ift88 gene resulting in a hypomorphic allele (Ift88Tg737Rpw). The Ift88Tg737Rpw mutation impairs intraflagellar transport (IFT), a process required for assembly of motile and immotile cilia. Historically, the primary immotile cilium was thought to have minimal importance for human health; however, a rapidly expanding number of human disorders have now been attributed to ciliary defects. Importantly, many of these phenotypes are present and can be analyzed using the ORPK mouse. In this review, we highlight the research conducted using the OPRK mouse and the phenotypes shared with human cilia disorders. Furthermore, we describe an additional follicular dysplasia phenotype in the ORPK mouse, which alongside the ectodermal dysplasias seen in human Ellis-van Creveld and Sensenbrenner's syndromes, suggests an unappreciated role for primary cilia in the skin and hair follicle.

Figure 1. Summary of phenotypes characterized in the ORPK mouse

The ORPK (FVB/N) mouse (left panels) has phenotypes in numerous tissues compared to wild type controls (right panels). (A) Cystic lesions are seen in the kidney. (B) The liver is characterized by biliary (arrow) and bile duct (arrow head) hyperplasia. Inset is a higher magnification view of a central vein showing the multiple dysplastic bile ductules. (C) In the pancreas, ducts become dilated (arrowhead) and acini atrophy (arrow). Insert shows the typical pancreatic phenotype seen in ORPK-C3H mutants (P is pancreas, L is liver, and K is kidney). (D) In contrast to wild type mice, the ORPK mutant has disrupted discs and outer segments that are misshapen and filled with amorphous material that extends into the inner segment of the rod and cone photoreceptors (data is from 10 day old mice, IS=inner segment, and CC=connecting cilium). The images were adapted with permission from Pazour et al. (Pazour et al., 2002a). Reproduced from The Journal of Cell Biology, 2002, 157:103-113. Copyright 2002 The Rockefeller University Press. (E) The ORPK mutants are ataxic due to hypoplasia of the cerebellum which is associated with loss of Shh signaling. Red bars indicate the length of the wild-type and ORPK cerebellum along the anteroposterior axis. Images adapted from Chizhikov et al. (Chizhikov et al., 2007). Copyright 2007 by the Society for Neuroscience. (F) ORPK mutants develop hydrocephalus. (G) ORPK mutants have defects in neuroblast migration. Shown are neuroblasts in whole mounts of the lateral ventricle stained with an antibody against Poly-Sialated Neural Cell Adhesion Molecule (PSA-NCAM). In wild type (WT) controls there are well-organized chains of neuroblasts migrating toward the olfactory bulb. In ORPK mutants, chains of neuroblasts form but the direction of migration is disorganized. Higher magnification views of the boxed region are shown in the inserts. Images were adapted from (Sawamoto et al., 2006). Reprinted with permission from AAAS. (H and I) ORPK mutants also exhibit numerous skeletal defects including preaxial polydactyly (H, arrow head) and formation of an extra molar tooth (I, labeled 0). Images adapted from Zhang et al. (Zhang et al., 2003) Copyright 2003 Wiley-Liss, Inc.

Figure 2. Gross epidermal and cilia phenotypes in the ORPK mouse

(A) Dry and flaky skin with sparse fur is noticeable in the ORPK mutant (right, C) by P16 compared to its wild type littermate control (left, B). (D-E) Primary cilia are found in the follicles of both adult (D) wild type and (E) ORPK mutant hair follicles by 3-D immunofluorescence confocal imaging for IFT88 (Red) and DAPI nuclear stain (Blue). (F-G) Higher magnification images of the cilia found in the hair follicle from the boxed regions in wild type (F) and ORPK (G) mutants. As seen in other tissues the primary cilia are stunted in ORPK mice compared to wild type controls.

Figure 3. Skin and follicular abnormalities in the ORPK mouse

At P1 (A) ORPK mice have mild growth delay with reduced adnexa in early follicular development compared to (D) wild type littermates. (E) P18 wild type littermates have normal follicles in telogen, whereas the skin of ORPK mice (B) is characterized by orthokeratotic hyperkeratosis, follicular accumulation of keratinaceous debris, and follicles in catagen. (H) Some follicles rupture, leading to a giant cell inflammatory response (arrow) and foreign body granulomas (trichogranulomas) (I, arrow). At P25, wild type follicles (F) are in anagen, whereas the follicles of ORPK mice (C) remain in first telogen. (G) Relative quantification of Shh pathway expression as determined by quantitative RT-PCR standardized to 18S RNA. Relative fold change was calculated by the 2^-ΔΔCT method by comparing the normalized gene expression level for each gene between the mutant and the control (±SD). Shh expression is identical between P14 ORPK skin and littermate controls, but downstream components of the pathway Ptch1 and Gli1 are downregulated. Scale bars= 50 microns.