LMNA variants cause cytoplasmic distribution of nuclear pore proteins in Drosophila and human muscle

Abstract

Mutations in the human LMNA gene, encoding A-type lamins, give rise to laminopathies, which include several types of muscular dystrophy. Here, heterozygous sequence variants in LMNA, which result in single amino-acid substitutions, were identified in patients exhibiting muscle weakness. To assess whether the substitutions altered lamin function, we performed in vivo analyses using a Drosophila model. Stocks were generated that expressed mutant forms of the Drosophila A-type lamin modeled after each variant. Larvae were used for motility assays and histochemical staining of the body-wall muscle. In parallel, immunohistochemical analyses were performed on human muscle biopsy samples from the patients. In control flies, muscle-specific expression of the wild-type A-type lamin had no apparent affect. In contrast, expression of the mutant A-type lamins caused dominant larval muscle defects and semi-lethality at the pupal stage. Histochemical staining of larval body wall muscle revealed that the mutant A-type lamin, B-type lamins, the Sad1p, UNC-84 domain protein Klaroid and nuclear pore complex proteins were mislocalized to the cytoplasm. In addition, cytoplasmic actin filaments were disorganized, suggesting links between the nuclear lamina and the cytoskeleton were disrupted. Muscle biopsies from the patients showed dystrophic histopathology and architectural abnormalities similar to the Drosophila larvae, including cytoplasmic distribution of nuclear envelope proteins. These data provide evidence that the Drosophila model can be used to assess the function of novel LMNA mutations and support the idea that loss of cellular compartmentalization of nuclear proteins contributes to muscle disease pathogenesis.

Nuclear matrix, nuclear envelope and premature aging syndromes in a translational research perspective

“…They allow the nuclear entry of proteins and the nuclear exit to the cytosol of nuclear proteins [226]. This increased NE permeability could be related to the redistribution of phenylalanine-glycine (FG) repeat-containing nucleoporins to the cytosol observed in human muscle cells bearing LMNA mutations [227]. Similar NE events have already observed during HIV [228] and adenoviral infection [229].…”

Unique and Shared Functions of Nuclear Lamina LEM Domain Proteins in Drosophila

“…Previous studies revealed that muscle-specific production of mutant Lamin C isoforms causes semilethality, with body wall muscles in larvae showing the formation of cytoplasmic aggregates of nuclear lamina components, such as the FGNups (Dialynas et al 2012). We wondered whether lethality of lem-d double mutants might be similarly related to muscle-specific dysfunction.…”

“…This model has been powerful in defining effects of novel disease-causing mutations in the human A-type lamin (Dialynas et al 2012), demonstrating that some disease-causing mutations cause a loss of nuclear compartmentalization of lamins and associated proteins, which may contribute to muscle disease. Drosophila encodes a three-member nuclear lamina LEM-D family ( Figure 1A).…”

Muscle development, regeneration and laminopathies: how lamins or lamina-associated proteins can contribute to muscle development, regeneration and disease

“…Exogenous MyoD enables muscle formation which is indiscernible from normal myogenesis with preservation of steps occurring in vivo and in vitro, including cell cycle withdrawal, subsequent expression of the proteins involved in the myogenic program (desmin, α-actinin, titin, troponin I, α-actin, myosin heavy chain) and fusion of the myoblasts into multinucleated myotubes (independent of surrounding extracellular matrix molecules). Activation of myogenesis leads to down regulation of the original differentiation program of the converted cell [64]. Transdifferentiation of various types of cell has been considered as medical treatment.…”