Mapping disease-related missense mutations in the immunoglobulin-like fold domain of lamin A/C reveals novel genotype-phenotype associations for laminopathies.

Mutations in A-type nuclear lamins cause laminopathies. However, genotype-phenotype correlations using the 340 missense mutations within the LMNA gene are unclear: partially due to the limited availability of three-dimensional structure. The immunoglobulin (Ig)-like fold domain has been solved, and using bioinformatics tools (including Polyphen-2, Fold X, Parameter OPtimized Surfaces, and PocketPicker) we characterized 56 missense mutations for position, surface exposure, change in charge and effect on Ig-like fold stability.

Defective skeletal muscle growth in lamin A/C-deficient mice is rescued by loss of Lap2α.

Mutations in lamin A/C result in a range of tissue-specific disorders collectively called laminopathies. Of these, Emery-Dreifuss and Limb-Girdle muscular dystrophy 1B mainly affect striated muscle. A useful model for understanding both laminopathies and lamin A/C function is the Lmna(-/-) mouse.

Nuclear envelope disease and chromatin organization.

The fifth U.K. meeting on nuclear envelope disease and chromatin brought together international experts from across the field of nuclear envelope biology to discuss the advancements in a class of tissue-specific degenerative diseases called the laminopathies.

Novel and recurrent EMD mutations in patients with Emery-Dreifuss muscular dystrophy, identify exon 2 as a mutation hot spot.

Emery-Dreifuss muscular dystrophy (EDMD) is a neuromuscular disorder exhibiting a cardiomyopathy with cardiac conduction defects. X-linked EDMD arises from mutations in the EMD gene, which encodes for a nuclear membrane protein termed emerin. In this study, we describe novel and recurrent EMD mutations identified in 18 probands and three carriers from a cohort of 255 North American patients referred for EDMD genetic mutation analysis.

Uncoordinated transcription and compromised muscle function in the lmna-null mouse model of Emery- Emery-Dreyfuss muscular dystrophy.

LMNA encodes both lamin A and C: major components of the nuclear lamina. Mutations in LMNA underlie a range of tissue-specific degenerative diseases, including those that affect skeletal muscle, such as autosomal-Emery-Dreifuss muscular dystrophy (A-EDMD) and limb girdle muscular dystrophy 1B. Here, we examine the morphology and transcriptional activity of myonuclei, the structure of the myotendinous junction and the muscle contraction dynamics in the lmna-null mouse model of A-EDMD.

Novel LMNA mutations in patients with Emery-Dreifuss muscular dystrophy and functional characterization of four LMNA mutations.

Mutations in LMNA cause a variety of diseases affecting striated muscle including autosomal Emery-Dreifuss muscular dystrophy (EDMD), LMNA-associated congenital muscular dystrophy (L-CMD), and limb-girdle muscular dystrophy type 1B (LGMD1B). Here, we describe novel and recurrent LMNA mutations identified in 50 patients from the United States and Canada, which is the first report of the distribution of LMNA mutations from a large cohort outside Europe. This augments the number of LMNA mutations known to cause EDMD by 16.

Genotype-phenotype correlations in laminopathies: how does fate translate?

A-type laminopathies are a group of diseases resulting from mutations in the intermediate filament proteins lamin A and C (both encoded by the LMNA gene), but for which the pathogenic mechanisms are little understood. In some laminopathies, there is a good correlation between the presence of a specific LMNA mutation and the disease diagnosed. In others however, many different mutations can give rise to the same clinical condition, even though the mutations may be distributed throughout one, or more, of the three functionally distinct protein domains of lamin A/C.

Identification of an emerin-beta-catenin complex in the heart important for intercalated disc architecture and beta-catenin localisation.

How mutations in the protein emerin lead to the cardiomyopathy associated with X-linked Emery-Dreifuss muscular dystrophy (X-EDMD) is unclear. We identified emerin at the adherens junction of the intercalated disc, where it co-localised with the catenin family of proteins. Emerin bound to wild type beta-catenin both in vivo and in vitro.

Mammalian SUN protein interaction networks at the inner nuclear membrane and their role in laminopathy disease processes.

The nuclear envelope (NE) LINC complex, in mammals comprised of SUN domain and nesprin proteins, provides a direct connection between the nuclear lamina and the cytoskeleton, which contributes to nuclear positioning and cellular rigidity. SUN1 and SUN2 interact with lamin A, but lamin A is only required for NE localization of SUN2, and it remains unclear how SUN1 is anchored. Here, we identify emerin and short nesprin-2 isoforms as novel nucleoplasmic binding partners of SUN1/2.

Defects in cell spreading and ERK1/2 activation in fibroblasts with lamin A/C mutations.

In-frame mutations in nuclear lamin A/C lead to a multitude of tissue-specific degenerative diseases known as the 'laminopathies'. Previous studies have demonstrated that lamin A/C-null mouse fibroblasts have defects in cell polarisation, suggesting a role for lamin A/C in nucleo-cytoskeletal-cell surface cross-talk. However, this has not been examined in patient fibroblasts expressing modified forms of lamin A/C.

Further characterisation of the molecular signature of quiescent and activated mouse muscle satellite cells.

Satellite cells are the resident stem cells of adult skeletal muscle. To date though, there is a paucity of native markers that can be used to easily identify quiescent satellite cells, with Pax7 probably being the best that is currently available. Here we have further characterized a number of recently described satellite cell markers, and also describe novel ones.

Molecular signatures of Emery-Dreifuss muscular dystrophy.

Mutations in genes encoding the nuclear envelope proteins emerin and lamin A/C lead to a range of tissue-specific degenerative diseases. These include dilated cardiomyopathy, limb-girdle muscular dystrophy and X-linked and autosomal dominant EDMD (Emery-Dreifuss muscular dystrophy). The molecular mechanisms underlying these disorders are poorly understood; however, recent work using animal models has identified a number of signalling pathways that are altered in response to the deletion of either emerin or lamin A/C or expression of Lmna mutants found in patients with laminopathies.

Does satellite cell dysfunction contribute to disease progression in Emery-Dreifuss muscular dystrophy?

Muscular dystrophies comprise at least 34 conditions, characterized by progressive skeletal muscle weakness and degeneration. The loci affected include mutations in both muscle-specific genes and genes that are more widely expressed such as LMNA and EMD, responsible for EDMD (Emery-Dreifuss muscular dystrophy). LMNA encodes A-type lamins, whereas EMD encodes emerin, both located in the nuclear envelope.

NEP-A and NEP-B both contribute to nuclear pore formation in Xenopus eggs and oocytes.

In vertebrates, the nuclear envelope (NE) assembles and disassembles during mitosis. As the NE is a complex structure consisting of inner and outer membranes, nuclear pore complexes (NPCs) and the nuclear lamina, NE assembly must be a controlled and systematic process. In Xenopus egg extracts, NE assembly is mediated by two distinct membrane vesicle populations, termed NEP-A and NEP-B.

Nesprin-1 and -2 are involved in the pathogenesis of Emery Dreifuss muscular dystrophy and are critical for nuclear envelope integrity.

Emery-Dreifuss muscular dystrophy (EDMD) is a heterogeneous late-onset disease involving skeletal muscle wasting and heart defects caused, in a minority of cases, by mutations in either of two genes encoding the inner nuclear membrane (INM) proteins, emerin and lamins A/C. Nesprin-1 and -2 are multi-isomeric, spectrin-repeat proteins that bind both emerin and lamins A/C and form a network in muscle linking the nucleoskeleton to the INM, the outer nuclear membrane, membraneous organelles, the sarcomere and the actin cytoskeleton. Thus, disruptions in nesprin/lamin/emerin interactions might play a role in the muscle-specific pathogenesis of EDMD.

Distinct functional domains in nesprin-1alpha and nesprin-2beta bind directly to emerin and both interactions are disrupted in X-linked Emery-Dreifuss muscular dystrophy.

Emerin and specific isoforms of nesprin-1 and -2 are nuclear membrane proteins which are binding partners in multi-protein complexes spanning the nuclear envelope. We report here the characterisation of the residues both in emerin and in nesprin-1alpha and -2beta which are involved in their interaction and show that emerin requires nesprin-1 or -2 to retain it at the nuclear membrane. Using several protein-protein interaction methods, we show that residues 368 to 627 of nesprin-1alpha and residues 126 to 219 of nesprin-2beta, which show high homology to one another, both mediate binding to emerin residues 140-176.

The Emery-Dreifuss muscular dystrophy associated-protein emerin is phosphorylated on serine 49 by protein kinase A.

Emerin is a ubiquitously expressed inner nuclear membrane protein of unknown function. Mutations in its gene give rise to X-linked Emery-Dreifuss muscular dystrophy (X-EDMD), a neuromuscular condition with an associated life-threatening cardiomyopathy. We have previously reported that emerin is phosphorylated in a cell cycle-dependent manner in human lymphoblastoid cell lines [Ellis et al.

The inner nuclear membrane protein emerin regulates beta-catenin activity by restricting its accumulation in the nucleus.

Emerin is a type II inner nuclear membrane (INM) protein of unknown function. Emerin function is likely to be important because, when it is mutated, emerin promotes both skeletal muscle and heart defects. Here we show that one function of Emerin is to regulate the flux of beta-catenin, an important transcription coactivator, into the nucleus.

Lamins A and C are differentially dysfunctional in autosomal dominant Emery-Dreifuss muscular dystrophy.

Mutations in the LMNA gene, which encodes nuclear lamins A and C by alternative splicing, can give rise to Emery-Dreifuss muscular dystrophy. The mechanism by which lamins A and C separately contribute to this molecular phenotype is unknown. To address this question we examined ten LMNA mutations exogenously expressed as lamins A and C in COS-7 cells.

Nesprin-2 is a multi-isomeric protein that binds lamin and emerin at the nuclear envelope and forms a subcellular network in skeletal muscle.

Nesprin-2 is a multi-isomeric, modular protein composed of variable numbers of spectrin-repeats linked to a C-terminal transmembrane domain and/or to N-terminal paired calponin homology (CH) domains. The smaller isoforms of nesprin-2 co-localize with and bind lamin A and emerin at the inner nuclear envelope (NE). In SW-13 cells, which lack lamin A/C, nesprin-2 epitopes and emerin were both mislocalized and formed aggregates in the endoplasmic reticulum (ER).

Muscular dystrophies, dilated cardiomyopathy, lipodystrophy and neuropathy: the nuclear connection.

An understanding of muscle structure and function is central to improving our knowledge of the group of muscle diseases referred to as muscular dystrophies. These diseases involve a progressive weakening and wasting of skeletal muscle, which can be associated with life-threatening cardiac arrhythmias. The vast majority of these diseases arise from defects in either cytoskeletal or structural proteins, resulting in a breakdown of muscle cell integrity.

The cell cycle dependent mislocalisation of emerin may contribute to the Emery-Dreifuss muscular dystrophy phenotype.

Emerin is the nuclear membrane protein defective in X-linked Emery-Dreifuss muscular dystrophy (X-EDMD). The majority of X-EDMD patients have no detectable emerin. However, there are cases that produce mutant forms of emerin, which can be used to study its function.