Identification of fibronectin 1 as a candidate genetic modifier in a Col4a1 mutant mouse model of Gould syndrome.

Mao Mao,Saunak Sen,Marion Jeanne,Tanav Popli,Douglas B Gould,Kendall Hoff

doi:10.1242/dmm.048231

Abstract

ABSTRACTCollagen type IV alpha 1 and alpha 2 (COL4A1 and COL4A2) are major components of almost all basement membranes. COL4A1 and COL4A2 mutations cause a multisystem disorder that can affect any organ but typically involves the cerebral vasculature, eyes, kidneys and skeletal muscles. In recent years, patient advocacy and family support groups have united under the name of Gould syndrome. The manifestations of Gould syndrome are highly variable, and animal studies suggest that allelic heterogeneity and genetic context contribute to the clinical variability. We previously characterized a mouse model of Gould syndrome caused by a Col4a1 mutation in which the severities of ocular anterior segment dysgenesis (ASD), myopathy and intracerebral hemorrhage (ICH) were dependent on genetic background. Here, we performed a genetic modifier screen to provide insight into the mechanisms contributing to Gould syndrome pathogenesis and identified a single locus [modifier of Gould syndrome 1 (MoGS1)] on Chromosome 1 that suppressed ASD. A separate screen showed that the same locus ameliorated myopathy. Interestingly, MoGS1 had no effect on ICH, suggesting that this phenotype could be mechanistically distinct. We refined the MoGS1 locus to a 4.3 Mb interval containing 18 protein-coding genes, including Fn1, which encodes the extracellular matrix component fibronectin 1. Molecular analysis showed that the MoGS1 locus increased Fn1 expression, raising the possibility that suppression is achieved through a compensatory extracellular mechanism. Furthermore, we found evidence of increased integrin-linked kinase levels and focal adhesion kinase phosphorylation in Col4a1 mutant mice that is partially restored by the MoGS1 locus, implicating the involvement of integrin signaling. Taken together, our results suggest that tissue-specific mechanistic heterogeneity contributes to the variable expressivity of Gould syndrome and that perturbations in integrin signaling may play a role in ocular and muscular manifestations.

Highlights

Collagens are the most abundant proteins in the body, making up ∼30% of the dry weight
We identified a region of interest on CAST Chr 1 with a logarithm of the odds (LOD) score of 11.2 and Bayesian confidence interval extending from 51.3 to 73.0 Mb (Fig. 1C)
Here, we performed a genetic modifier screen in Col4a1 mutant mice to gain insight into the pathogenic mechanisms that contribute to Gould syndrome

Summary

Introduction

Collagens are the most abundant proteins in the body, making up ∼30% of the dry weight. The collagen superfamily of extracellular matrix (ECM) molecules comprises 28 members encoded by 46 genes (Ricard-Blum, 2011). Type IV collagens are primordial ECM molecules and are fundamental constituents of specialized structures called basement membranes (Fidler et al, 2017). Six genes encode the type IV collagens (Col4a1 to Col4a6) and their protein products assemble into three distinct heterotrimers [α1α1α2(IV), α3α4α5(IV) or α5α5α6(IV)]. Studies in humans and mice have subsequently expanded the phenotypic spectrum, and it is well established that mutations in COL4A1 and COL4A2 cause a multisystem syndrome (Jeanne and Gould, 2017; Labelle-Dumais et al, 2019; Mao et al, 2015; Meuwissen et al, 2015; Yoneda et al, 2013; Zagaglia et al, 2018)

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