Zebrafish mbnl mutants model physical and molecular phenotypes of myotonic dystrophy.

Melissa N Hinman,Rose A Sockol,Sarah J Stednitz,J Andrew Berglund,Eliza D Aronson,Katrina N Murray,Karen Guillemin,Jared I Richardson

doi:10.1242/dmm.045773

Abstract

ABSTRACTThe muscleblind RNA-binding proteins (MBNL1, MBNL2 and MBNL3) are highly conserved across vertebrates and are important regulators of RNA alternative splicing. Loss of MBNL protein function through sequestration by CUG or CCUG RNA repeats is largely responsible for the phenotypes of the human genetic disorder myotonic dystrophy (DM). We generated the first stable zebrafish (Danio rerio) models of DM-associated MBNL loss of function through mutation of the three zebrafish mbnl genes. In contrast to mouse models, zebrafish double and triple homozygous mbnl mutants were viable to adulthood. Zebrafish mbnl mutants displayed disease-relevant physical phenotypes including decreased body size and impaired movement. They also exhibited widespread alternative splicing changes, including the misregulation of many DM-relevant exons. Physical and molecular phenotypes were more severe in compound mbnl mutants than in single mbnl mutants, suggesting partially redundant functions of Mbnl proteins. The high fecundity and larval optical transparency of this complete series of zebrafish mbnl mutants will make them useful for studying DM-related phenotypes and how individual Mbnl proteins contribute to them, and for testing potential therapeutics.This article has an associated First Person interview with the first author of the paper.

Highlights

The muscleblind (MBNL) family of RNA-binding proteins (MBNL1, MBNL2 and MBNL3) is highly conserved in structure and function across multicellular species (Oddo et al, 2016)
All homozygous mbnl1, mbnl2 and mbnl3 mutants survived to adulthood in roughly Mendelian ratios (Table S3), were fertile, and did not exhibit the dramatic morphological phenotypes that were previously observed in mbnl2 morpholino-injected larvae (MachucaTzili et al, 2011)
Our analysis of previously published RNA sequencing (RNA-Seq) data (Mehjabin et al, 2019) indicated that all three mbnl mRNAs were present at low or very low levels in wild-type (WT) unfertilized eggs (Fig. S1G), consistent with a previous report that only maternally deposited mRNAs of mbnl1 and mbnl2 could be detected by non-quantitative reverse transcription PCR (RT-PCR) (Liu et al, 2008)

Summary

Introduction

The muscleblind (MBNL) family of RNA-binding proteins (MBNL1, MBNL2 and MBNL3) is highly conserved in structure and function across multicellular species (Oddo et al, 2016). Elizabeth Patton Received 15 May 2020; Accepted 4 May 2021 in target RNAs and regulate multiple aspects of RNA metabolism, including alternative splicing (Ashwal-Fluss et al, 2014; Batra et al, 2014; Goers et al, 2010; Grammatikakis et al, 2011; Ho et al, 2004; Rau et al, 2011; Wang et al, 2012; Warf and Berglund, 2007). MBNL proteins promote exon skipping or inclusion when bound to introns upstream or downstream of an alternative exon, respectively (Du et al, 2010; Goers et al, 2010; Wang et al, 2012). Regulation of alternative splicing by MBNL proteins influences the molecular and biological functions of hundreds of target genes

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