WDR81 Is Necessary for Purkinje and Photoreceptor Cell Survival

Abstract

The gene encoding the WD repeat-containing protein 81 (WDR81) has recently been described as the disease locus in a consanguineous family that suffers from cerebellar ataxia, mental retardation, and quadrupedal locomotion syndrome (CAMRQ2). Adult mice from the N-ethyl-N-nitrosourea-induced mutant mouse line nur5 display tremor and an abnormal gait, as well as Purkinje cell degeneration and photoreceptor cell loss. We have used polymorphic marker mapping to demonstrate that affected nur5 mice carry a missense mutation, L1349P, in the Wdr81 gene. Moreover, homozygous nur5 mice that carry a wild-type Wdr81 transgene are rescued from the abnormal phenotype, indicating that Wdr81 is the causative gene in nur5. WDR81 is expressed in Purkinje cells and photoreceptor cells, among other CNS neurons, and like the human mutation, the nur5 modification lies in the predicted major facilitator superfamily domain of the WDR81 protein. Electron microscopy analysis revealed that a subset of mitochondria in Purkinje cell dendrites of the mutant animals displayed an aberrant, large spheroid-like structure. Moreover, immunoelectron microscopy and analysis of mitochondrial-enriched cerebellum fractions indicate that WDR81 is localized in mitochondria of Purkinje cell neurons. Because the nur5 mouse mutant demonstrates phenotypic similarities to the human disease, it provides a valuable genetic model for elucidating the pathogenic mechanism of the WDR81 mutation in CAMRQ2.

Mini-Exome Coupled to Read-Depth Based Copy Number Variation Analysis in Patients with Inherited Ataxias

“…In patient ATX478, we found two compound heterozygous missense mutations in WDR81 (Wd Repeat‐Containing Protein 81, MIM# 614218), responsible for Cerebellar Ataxia, Mental Retardation, and disequilibrium syndrome 2 (CAMRQ2, MIM# 610185), combining cerebellar ataxia, mental retardation and peculiar ophthalmologic findings [Gulsuner et al., ; Sarac et al., ]: moreover a Wdr81 ‐mutated mouse model showed selective cerebellar and retinal involvement [Traka et al., ]. In this patient, the combination of early onset cerebellar ataxia and retinopathy could be in favor of WDR81 involvement; however, pathogenicity prediction of the two WDR81 missense mutations is un‐conclusive (Table ) and no biological marker is available to evaluate WDR81 implication.…”

Pathogenesis of severe ataxia and tremor without the typical signs of neurodegeneration

“…Genetic studies in mice and zebrafish show that loss of these genes mimics the main behavioral features of the human condition, and in each case Purkinje cells are the primary target (Jiao et al, 2005, Trommsdorff et al, 1999, Traka et al, 2013, Aspatwar et al, 2012). And, although Purkinje cell degeneration is a recurring feature of motor disease, it is intriguing that behavior can be affected early in life and without obvious structural pathology in the cerebellum (White et al, 2014).…”

Analysis of Brain Mitochondria Using Serial Block-Face Scanning Electron Microscopy

“…Earlier SBFSEM analysis was greatly hindered due to lower resolution, however newer sample preparation techniques involving enhanced staining methods 40 have considerably improved the resolution to an extent that even a single synaptic vesicle can be easily resolved. At this resolution ultrastructural defects in mitochondria such as vacuolation, membrane disruption, and loss of cristae can be easily observed, and the distribution of defective mitochondria within cells can be determined 38,39 . The high resolution of this technique provides a major advantage over light microscopy where the resolution is limited to ~200 nm in XY axis and ~500 nm in Z-axis.…”

“…Multiple studies since then have established this technique as a major tool in reconstruction analysis of neuronal circuitry 34 . Furthermore, for many smaller scale projects, it provides reconstruction analysis to identify cellular organelles 27,[35][36][37][38][39] . Since, the acquired images are derived from low voltage back scatter electrons, new staining protocols which combine different known heavy metal staining techniques were developed to increase the resolution 40 .…”

“…In this paper, we provide a protocol for utilizing 3D electron microscopy imaging and volumetric analysis of brain mitochondria based on methods that have previously been used by us and others 38,39,41 . The tissue post-processing methods used were as previously described by Deerinck et al 40 .…”