title: An RMND1 Mutation causes encephalopathy associated with multiple oxidative phosphorylation complex deficiencies and a mitochondrial translation defect.
abstract: Mutations in the genes composing the mitochondrial translation apparatus are an important cause of a heterogeneous group of oxidative phosphorylation (OXPHOS) disorders. We studied the index case in a consanguineous family in which two children presented with severe encephalopathy, lactic acidosis, and intractable seizures leading to an early fatal outcome. Blue native polyacrylamide gel electrophoretic (BN-PAGE) analysis showed assembly defects in all of the OXPHOS complexes with mtDNA-encoded structural subunits, and these defects were associated with a severe deficiency in mitochondrial translation. Immunoblot analysis showed reductions in the steady-state levels of several structural subunits of the mitochondrial ribosome. Whole-exome sequencing identified a homozygous missense mutation (c.1250G>A) in an uncharacterized gene, RMND1 (required for meiotic nuclear division 1). RMND1 localizes to mitochondria and behaves as an integral membrane protein. Retroviral expression of the wild-type RMND1 cDNA rescued the biochemical phenotype in subject cells, and siRNA-mediated knockdown of the protein recapitulated the defect. BN-PAGE, gel filtration, and mass spectrometry analyses showed that RMND1 forms a high-molecular-weight and most likely homopolymeric complex (∼240 kDa) that does not assemble in subject fibroblasts but that is rescued by expression of RMND1 cDNA. The p.Arg417Gln substitution, predicted to be in a coiled-coil domain, which is juxtaposed to a transmembrane domain at the extreme C terminus of the protein, does not alter the steady-state level of RMND1 but might prevent protein-protein interactions in this complex. Our results demonstrate that the RMND1 complex is necessary for mitochondrial translation, possibly by coordinating the assembly or maintenance of the mitochondrial ribosome.
authors.affiliation: Department of Human Genetics, McGill University, 1205 Penfield Avenue, Montréal, QC H3A 1B1, Canada.
authors.forename: Alexandre
authors.initials: A
authors.lastname: Janer
authors.forename: Hana
authors.initials: H
authors.lastname: Antonicka
authors.forename: Emilie
authors.initials: E
authors.lastname: Lalonde
authors.forename: Tamiko
authors.initials: T
authors.lastname: Nishimura
authors.forename: Florin
authors.initials: F
authors.lastname: Sasarman
authors.forename: Garry K
authors.initials: GK
authors.lastname: Brown
authors.forename: Ruth M
authors.initials: RM
authors.lastname: Brown
authors.forename: Jacek
authors.initials: J
authors.lastname: Majewski
authors.forename: Eric A
authors.initials: EA
authors.lastname: Shoubridge
mesh_terms: D018797:Cell Cycle Proteins / Q000235:genetics*; D003241:Consanguinity; D004272:DNA, Mitochondrial / Q000235:genetics; D059472:Exome; D005260:Female; D020022:Genetic Predisposition to Disease; D006720:Homozygote; D006801:Humans; D007231:Infant, Newborn; D008607:Intellectual Disability / Q000235:genetics*; D065768:Lennox Gastaut Syndrome; D008565:Membrane Proteins / Q000235:genetics; D008928:Mitochondria / Q000235:genetics*; D028361:Mitochondrial Diseases / Q000235:genetics*; D024101:Mitochondrial Proteins / Q000235:genetics*; D020125:Mutation, Missense; D010641:Phenotype; D014176:Protein Biosynthesis; D054730:Protein Interaction Domains and Motifs / Q000235:genetics; D012270:Ribosomes / Q000235:genetics; D013036:Spasms, Infantile / Q000235:genetics*
chemical_list: D018797:Cell Cycle Proteins; D004272:DNA, Mitochondrial; D008565:Membrane Proteins; D024101:Mitochondrial Proteins; C578871:RMND1 protein, human