Interpreting the pathogenicity of Joubert syndrome missense variants in Caenorhabditis elegans.

Karen I Lange,Oliver E Blacque,Katarzyna Kucharska,Sofia Tsiropoulou

doi:10.1242/dmm.046631

Abstract

ABSTRACTCiliopathies are inherited disorders caused by defects in motile and non-motile (primary) cilia. Ciliopathy syndromes and associated gene variants are often highly pleiotropic and represent exemplars for interrogating genotype-phenotype correlations. Towards understanding disease mechanisms in the context of ciliopathy mutations, we have used a leading model organism for cilia and ciliopathy research, Caenorhabditis elegans, together with gene editing, to characterise two missense variants (P74S and G155S) in mksr-2/B9D2 associated with Joubert syndrome (JBTS). B9D2 functions within the Meckel syndrome (MKS) module at the ciliary base transition zone (TZ) compartment and regulates the molecular composition and sensory/signalling functions of the cilium. Quantitative assays of cilium/TZ structure and function, together with knock-in reporters, confirm that both variant alleles are pathogenic in worms. G155S causes a more severe overall phenotype and disrupts endogenous MKSR-2 organisation at the TZ. Recapitulation of the patient biallelic genotype shows that compound heterozygous worms phenocopy worms homozygous for P74S. The P74S and G155S alleles also reveal evidence of a very close functional association between the B9D2-associated B9 complex and MKS-2/TMEM216. Together, these data establish C. elegans as a model for interpreting JBTS mutations and provide further insight into MKS module organisation.This article has an associated First Person interview with the first author of the paper.

Highlights

Ciliopathy disorders affect the development and/or homeostasis of many body tissues and organs and consist of at least 35 clinically distinct genetically inherited diseases
Modelling pathogenic missense B9D2 variants associated with Joubert syndrome Human B9D2 and the C. elegans MKSR-2 orthologue possess 63.4% amino acid similarity (100% length, BLAST e-value 3×10−52; Fig. 1A)
MKSR-2 distribution at the transition zone (TZ) is severely altered by the G155S mutation First, we investigated whether the P74S and G155S mutations affect the TZ localisation of MKSR-2

Summary

Introduction

Ciliopathy disorders affect the development and/or homeostasis of many body tissues and organs and consist of at least 35 clinically distinct genetically inherited diseases. Ciliopathies result from defects in motile or primary cilia that extend from the surfaces. Non-motile primary cilia function as antenna-like organelles, responding to many extracellular sensory cues, such as light, odorants and osmotic strength, in addition to cell-cell signalling molecules (e.g. sonic hedgehog) that regulate cell behaviour, tissue formation and homeostasis (Anvarian et al, 2019). The canonical primary cilium consists of a cylinder of nine doublet microtubules extending from a plasma membrane-anchored basal body (Satir et al, 2010)

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