title: The molecular basis of variable phenotypic severity among common missense mutations causing Rett syndrome.
abstract: Rett syndrome is caused by mutations in the X-linked MECP2 gene, which encodes a chromosomal protein that binds to methylated DNA. Mouse models mirror the human disorder and therefore allow investigation of phenotypes at a molecular level. We describe an Mecp2 allelic series representing the three most common missense Rett syndrome (RTT) mutations, including first reports of Mecp2[R133C] and Mecp2[T158M] knock-in mice, in addition to Mecp2[R306C] mutant mice. Together these three alleles comprise ∼25% of all RTT mutations in humans, but they vary significantly in average severity. This spectrum is mimicked in the mouse models; R133C being least severe, T158M most severe and R306C of intermediate severity. Both R133C and T158M mutations cause compound phenotypes at the molecular level, combining compromised DNA binding with reduced stability, the destabilizing effect of T158M being more severe. Our findings contradict the hypothesis that the R133C mutation exclusively abolishes binding to hydroxymethylated DNA, as interactions with DNA containing methyl-CG, methyl-CA and hydroxymethyl-CA are all reduced in vivo. We find that MeCP2[T158M] is significantly less stable than MeCP2[R133C], which may account for the divergent clinical impact of the mutations. Overall, this allelic series recapitulates human RTT severity, reveals compound molecular aetiologies and provides a valuable resource in the search for personalized therapeutic interventions.
authors.affiliation: Wellcome Trust Centre for Cell Biology, University of Edinburgh, Michael Swann Building, Max Born Crescent, Edinburgh EH9 3BF, UK.
authors.forename: Kyla
authors.initials: K
authors.lastname: Brown
authors.affiliation: Wellcome Trust Centre for Cell Biology, University of Edinburgh, Michael Swann Building, Max Born Crescent, Edinburgh EH9 3BF, UK.
authors.forename: Jim
authors.initials: J
authors.lastname: Selfridge
authors.affiliation: Wellcome Trust Centre for Cell Biology, University of Edinburgh, Michael Swann Building, Max Born Crescent, Edinburgh EH9 3BF, UK.
authors.forename: Sabine
authors.initials: S
authors.lastname: Lagger
authors.affiliation: Wellcome Trust Centre for Cell Biology, University of Edinburgh, Michael Swann Building, Max Born Crescent, Edinburgh EH9 3BF, UK.
authors.forename: John
authors.initials: J
authors.lastname: Connelly
authors.affiliation: Wellcome Trust Centre for Cell Biology, University of Edinburgh, Michael Swann Building, Max Born Crescent, Edinburgh EH9 3BF, UK.
authors.forename: Dina
authors.initials: D
authors.lastname: De Sousa
authors.affiliation: Wellcome Trust Centre for Cell Biology, University of Edinburgh, Michael Swann Building, Max Born Crescent, Edinburgh EH9 3BF, UK.
authors.forename: Alastair
authors.initials: A
authors.lastname: Kerr
authors.affiliation: Wellcome Trust Centre for Cell Biology, University of Edinburgh, Michael Swann Building, Max Born Crescent, Edinburgh EH9 3BF, UK.
authors.forename: Shaun
authors.initials: S
authors.lastname: Webb
authors.affiliation: Wellcome Trust Centre for Cell Biology, University of Edinburgh, Michael Swann Building, Max Born Crescent, Edinburgh EH9 3BF, UK.
authors.forename: Jacky
authors.initials: J
authors.lastname: Guy
authors.affiliation: Wellcome Trust Centre for Cell Biology, University of Edinburgh, Michael Swann Building, Max Born Crescent, Edinburgh EH9 3BF, UK.
authors.forename: Cara
authors.initials: C
authors.lastname: Merusi
authors.affiliation: Wellcome Trust Centre for Cell Biology, University of Edinburgh, Michael Swann Building, Max Born Crescent, Edinburgh EH9 3BF, UK.
authors.forename: Martha V
authors.initials: MV
authors.lastname: Koerner
authors.affiliation: Wellcome Trust Centre for Cell Biology, University of Edinburgh, Michael Swann Building, Max Born Crescent, Edinburgh EH9 3BF, UK a.bird@ed.ac.uk.
authors.forename: Adrian
authors.initials: A
authors.lastname: Bird
mesh_terms: D000483:Alleles; D019943:Amino Acid Substitution; D000818:Animals; D004247:DNA / Q000235:genetics / Q000378:metabolism; D019175:DNA Methylation; D004195:Disease Models, Animal; D005786:Gene Expression Regulation; D055879:Gene Knock-In Techniques; D006801:Humans; D008297:Male; D051783:Methyl-CpG-Binding Protein 2 / Q000235:genetics* / Q000378:metabolism; D051379:Mice; D008822:Mice, Transgenic; D008958:Models, Molecular; D020125:Mutation, Missense; D010641:Phenotype; D011485:Protein Binding; D015518:Rett Syndrome / Q000235:genetics* / Q000378:metabolism / Q000401:mortality / Q000473:pathology*; D012720:Severity of Illness Index; D015398:Signal Transduction; D016019:Survival Analysis
chemical_list: C497392:MECP2 protein, human; D051783:Methyl-CpG-Binding Protein 2; D004247:DNA