title: Mechanisms underlying intranuclear rod formation.
abstract: Specific mutations within the alpha-skeletal actin gene (ACTA1) result in intranuclear rod myopathy (IRM), characterized by rod-like aggregates containing actin and alpha-actinin-2 inside the nucleus of muscle cells. The mechanism leading to formation of intranuclear aggregates containing sarcomeric proteins and their impact on cell function and contribution to disease pathogenesis is unknown. In this study, we transfected muscle and non-muscle cells with mutants of alpha-skeletal actin (Val163Leu, Val163Met) associated with intranuclear rod myopathy. By live-cell imaging we demonstrate that nuclear aggregates of actin form within the nuclear compartment, rather than entering the nucleus after formation in the cytoplasm, and are highly motile and dynamic structures. Thus, the nuclear environment supports the polymerization of actin and the movement and coalescence of the polymerized actin into larger structures. We show that the organization of actin within these aggregates is influenced by the binding of alpha-actinin, and that alpha-actinin is normally present in the nucleus of muscle and non-muscle cells. Furthermore, we demonstrate that, under conditions of cell stress (cytoskeletal disruption and ATP depletion), WT skeletal actin forms aggregates within the nucleus that are similar in morphology to those formed by the mutant actin, suggesting a common pathogenic mechanism for aggregate formation. Finally, we show that the presence of intranuclear actin aggregates significantly decreases the mitotic index and hence impacts on the function of the cell. Intranuclear aggregates thus likely contribute to the pathogenesis of muscle weakness in intranuclear rod myopathy.
authors.affiliation: Institute for Neuromuscular Research, Children's Hospital at Westmead, NSW, Australia.
authors.forename: Ana
authors.initials: A
authors.lastname: Domazetovska
authors.forename: Biljana
authors.initials: B
authors.lastname: Ilkovski
authors.forename: Sandra T
authors.initials: ST
authors.lastname: Cooper
authors.forename: Majid
authors.initials: M
authors.lastname: Ghoddusi
authors.forename: Edna C
authors.initials: EC
authors.lastname: Hardeman
authors.forename: Laurie S
authors.initials: LS
authors.lastname: Minamide
authors.forename: Peter W
authors.initials: PW
authors.lastname: Gunning
authors.forename: James R
authors.initials: JR
authors.lastname: Bamburg
authors.forename: Kathryn N
authors.initials: KN
authors.lastname: North
mesh_terms: D008841:Actin Cytoskeleton / Q000502:physiology; D000185:Actinin / Q000235:genetics / Q000378:metabolism; D000199:Actins / Q000235:genetics* / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002467:Cell Nucleus / Q000378:metabolism; D002478:Cells, Cultured; D051379:Mice; D008940:Mitotic Index; D009154:Mutation; D017696:Myopathies, Nemaline / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D014162:Transfection
chemical_list: D000199:Actins; D000185:Actinin; D000255:Adenosine Triphosphate