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Lamin A/C (LMNA)

( LGMD1B, CMD1A, EDMD2/3, (F)PLD, CMT2B1, MAD, HGPS, LDHPC, WRN, CCPS, RD )

(last modified July 5, 2005)

Contents

• Summary
• The lamin A/C gene
  • summary table
• The lamin A/C mRNA
  • lamin A/C expression
• The lamin A/C protein
  • lamin A/C antibodies
• lamin A/C and disease:  LGMD1B, EDMD2, EDMD3, CMD1A, FPLD, CMT2B1, MAD, HGPS, WRN, CCPS
  • LMNA sequence variants (mutations and polymorphisms)
• Miscellaneous
  • DNA-primers
  • RNA-primers
  • lamin A/C sequences

Summary

Lamins are intermediate filament-type proteins which form major components of the nuclear lamina. Lamins form dimers through their rod domain and interact with chromatin and integral proteins of the inner nuclear membrane through binding sites located in their carboxy-terminal globular tail. Mammals have two main type lamins, A and B. B-type lamins B1 and B2 are encoded by two distinct genes, LMNB1 and LMNB2 (Höger et al., 1990). Lamin B3 is germ cell specific protein generated by differential splicing and alternative polyadenylation of the LMNB2 gene (Furukawa & Hotta, 1993). A-type lamins A and C are derived by differential splicing and alternative polyadenylation from one gene, the LMNA gene. Mutations in LMNA have been shown to cause a whole range of human disorders, including autosomal dominant and recessive forms of Emery-Dreifuss muscular dystrophy (EDMD2/3), Limb-Girdle muscular dystrophy (LGMD1B), dilated cardiomyopathy (conduction-system disease, CMD1A), familial autosomal dominant partial lipodystrophy (Dunnigan variety, FPLD), autosomal recessive Charcot-Marie-Tooth disease (CMT2B1), mandibuloacral dysplasia  (MAD),  Hutchinson-Gilford progeria syndrome (HGPS), lipoatrophy with diabetes, hepatic steatosis, hypertrophic cardiomyopathy and leukomelanodermic papules (LDHPC), Werner's syndrome (WRN), cardiocutaneous progeria syndrome (CCPS) and Restrictive Dermopathy (RD).

The lamin A/C gene

Links to other databases:
Gene Symbol nomenclature   LocusLink    OMIM Gene Map   GDB

The LGMB-1B locus was mapped to chromosome 1q11-q21 in .... 

The lamin A/C gene (Gene Symbol LMNA, alternatives CMD1A, EMD2, FPL, FPLD, LFP, LDP1, LMN1, LMNC) maps to chromosome1q21.2-q21.3. The gene is flanked by RAB25 and FLJ12287 (NM_022367). The LMNA gene has 12 exons. The gene measures 57.6 kb. Lamin C is derived from the LMNA gene using an alternative splice site located in intron 10; Lamin C thus differs C-terminally from the lamin A. 

Legend:
Exon: numbering of exons and intron/exon boundaries are according to ... with the first base of the Met-codon counted as position 1 (see Reference Sequence). Exon size: size of exon indicated in basepairs. Intron size: size of intron indicated in kilobasepairs. 5' cDNA position: first base of the exon (according to cDNA sequence reported by ...). Splice after: splicing occurs in between of two coding triplets (0), after the first (1) or the second (2) base of a triplet. Remarks: 5'UTR = 5' untranslated region, 3'UTR = 3' untranslated region.

primers for DNA-amplification

The lamin A/C mRNA

Links to other databases:     UniGene: Hs.77886    RefSeq: NM_170707 (lamin A, isoform 1), NM_005572 (lamin C, isoform 2), NM_170708 (laminAdel10, isoform 3)

On Northern-blot, LMNA RNA expression reveals two clear bands. The upper band represents the lamin A, the lower band the lamin C transcript.

Machiels et al. (1995) detected an irregular A-type lamin protein in intranuclear aggregates of GLC-A1 cells, a lung carcinoma cell line. Later, using RT-PCR specifically directed to the region from exon 6 to 12, the authors (Machiels et al., 1996) detected an alternatively spliced lamin A-type which lacks exon 10 (90 bp smaller). The new isoform, designated lamin Adel10, was present in all RNA's tested (several tissues and cell lines), although at different levels.

The expression of A-type lamins is developmentally regulated. In mouse, A-type lamins are absent from all pre-implantation stage embryonic cells (including embryonal carcinoma cells). Expression appears at about embryonic day 9 within the visceral endoderm and the trophoblast (Stewart & Burke 1987). Later, A-type lamins appear asynchronously in various tissues. In certain cell types the proteins do not appear until after birth (Rober et al. 1989). A few cells, i.e. cells of the immune system, pancreatic islets and Purkinje cells, only express B-type lamins (Rober et al. 1990). These findings indicate that at the cellular level, A-type lamins are nonessential.

primers for RNA-amplification

The lamin A/C protein

Links to other databases:   RefSeq: NP_005563 NP_733821 (lamin A), NP_005563 (lamin C), NP_733822 (laminAdel10)

Lamin A/C is an Intermediate Filament protein. IF proteins are primordial components of the cytoskeleton and the nuclear envelope. They generally form filamentous structures 8 to 14 nm wide. IF proteins are members of a very large multigene family of proteins which has been subdivided in five major subgroups (see SwissProt, PFAM00038); 

• type I: acidic cytokeratins
• type II: basic cytokeratins
• type III: vimentin, desmin, glial fibrillary acidic protein (GFAP), peripherin, and plasticin
• type IV: neurofilaments L, H and M, alpha-internexin and nestin
• type V: nuclear lamins A, B1, B2 and C. 

Lamin A/C is a type V nuclear lamin. The lamins are components of the nuclear lamina, a fibrous layer on the nucleoplasmic side of the inner nuclear membrane which is suggested to provide a framework for the nuclear envelope and may interact with chromatin.

All IF proteins are structurally similar and consist of;

• a central rod domain comprising some 300 to 350 residues arranged in coiled-coiled alpha-helices, with at least two short characteristic interruptions
• an N-terminal non-helical domain (head) of variable length
• a non-helical C-terminal domain (tail) which shows extreme length variation between different IF proteins

While IF proteins are evolutionary and structurally related, they have limited sequence homologies except in several regions of the rod domain.

Lamin A is a 664 amino acid protein with a molecular weight of 70 kDa (calculated 74,139 Da) and a pI of 7.0 (theoretical pI 7.4). Lamin A consists of a central rod domain flanked by hydrophobic N- and C-terminal domains. After farnesylation at the CAAX-box motif, the 18 most C-terminal amino acids of lamin-A are removed by proteolytic cleavage to generate the mature lamin-A protein (Hennekes & Nigg). Lamin C (572 amino acids) differs from lamin A after amino acid 566, containing an alternative 6 amino acid C-terminal end (VSGSRR). Lamin Adel10 has a Mw of 65 kDa and a pI of 8 (theoretical pI 8.58). It lacks the region encoded by exon 10 , resulting in the loss of an acidic and a polyhistidine domain. 

Lamin A/C contains several protein domains;

Ser22 is phosphorylated in cdc2 pathways (Draetta [1990], Nigg [1992]), inhibiting head-to-tail assembly of lamins (Peter 1990). Mutations in the phosphoacceptor site strongly interfere with lamina disassembly (Heald & McKeon 1990). Lamins A/C form dimers through their rod domain (...). They bind and assemble on the surface of mitotic chromosomes at specific sites on the rod and associate with integral proteins of the nuclear envelope (like lamin-associated polypeptides 1A and 1B, lamin B receptor and emerin).

See also Functionally tested variants.

lamin A/C antibodies

Novelli et al. (2002) describe the use of monoclonal anti-LMNA antibody 4A7 (kindly provided by G. Morris).

lamin A/C and disease: LGMD-1B

Links to other databases:   OMIM: 181350 (EDMD2); 604929 (EDMD3); 159001 (LGMD1B); 115200 (CMD1A); 151660 (FPLD); CMT2B1 (605588); 248370 (MAD); 176670 (HGPS); 608056 (LDHPC); 277700 (WRN); OMIM- (CCPS); OMIM: 275210 (RD)

LGMB-1B is an autosomal dominantly inherited, slowly progressive limb girdle muscular dystrophy. LGMD-1B patients present with slowly progressive pelvic girdle weakness with late involvement of humeral muscles and sparing of the peroneal and tibial muscles, age-related atrioventricular cardiac conduction disturbances and dilated cardiomyopathy. The disease was linked to chromosome 1q11-q21, with maximum LOD-scores >6 at theta=0 (van der Kooi et al., 1997). The region contained the LMNA-gene shown by Bonne et al. to be mutated in the autosomal dominant form of Emery-Dreifuss muscular dystrophy (AD-EDMD). To identify whether or not LGMD1B and AD-EDMD are allelic disorders, Muchir et al. performed a search for mutations in the LMNA gene in patients from three LGMD1B families linked to chromosome 1q11-q21. Mutations were identified in all affected members of the three families: a missense mutation, a deletion of a codon and a splice donor site mutation, respectively (Muchir).

Mutations in lamin A/C have been shown to cause a series of diseases (lamin A/C sequence variation database);

• LGMD1B; see above
• EDMD2 / EDMD3; autosomal dominant (EDMD2, EDMD-AD) and autosomal recessive (EDMD3, EDMD-AR) forms of Emery-Dreifuss muscular dystrophy. EDMD are characterized by early contractures of elbows and Achilles tendons, a slowly progressing muscle waisting and weakness and a life-threatening cardiomyopathy with conduction blocks. Three modes of inheritance exist, X-linked (OMIM: 310300), autosomal dominant (OMIM: 181350) and autosomal recessive (OMIM: 604929).
• CDM1A; cardiomyopathy, dilated, type 1A (conduction-system disease) (OMIM: 115200)
• FPLD; familial autosomal dominant partial lipodystrophy (Dunnigan variety), a degenerative disorder of the adipose tissue (OMIM: 151660)
• CMT2B1; autosomal recessive Charcot-Marie-Tooth disorder type 2 (AR-CMT2, OMIM: 605588). Main clinical symptoms in 90% of cases are early onset, symmetrical muscle weakness and wasting (predominantly in the distal lower limbs), foot deformities and walking difficulties associated with reduced or absent tendon reflexes (De Jonghe et al. 1998, Gemignani et al. 2001). Confirmation of diagnosis relies essentially on electrophysiology, showing NCVs >38 m/s at the median nerve and on histopathology after nerve biopsy, showing a loss of myelinated fibers with (for AD-CMT2) or without (for AR-CMT2) regenerative attempts (De Jonghe et al. 1998, Gemignani et al. 2001). De Sandre-Giovannoli et al. (2002) reported a mutation in the LMNA gene in two consanguineous Algerian families.
• MAD; mandibuloacral dysplasia (OMIM: 248370). Main clinical symptoms are mandibular and clavicular hypoplasia, acroosteolysis, delayed closure of the cranial suture, joint contractures and types A and B patterns of lipodystrophy (Simha & Garg, 2002). Novelli et al. (2002) identified 5 consanguineous MAD families with 9 patients, all from a sparsely populated area from central Italy. The patients showed no detectable muscle wasting or weakness and creatine kinase levels were normal. Patients reported no cardiac symptoms and electrocardiograms were normal. The lipodystrophy features of the patients made the authors test the LMNA gene as a candidate. First, linkage analysis of the chromosome 1q21 region surrounding the LMNA gene was performed. Mulitpoint analysis identified linkage with a maximum LOD score of 9.05 in the interval defined by D1S2715 and D1S2721 (both were homozygous). Sequence analysis revealed a homozygous c.1580G>A (p.Arg527His) change in exon 9 in all patients. Heterozygous parents were healthy and showed no disease features. 
• HGPS; Hutchinson-Gilford progeria syndrome (OMIM: 176670) is a rare genetic disorder characterized by premature senescence, both clinically and in cell culture. Affected children appear normal at birth, but within a year develop characteristic features of failure to thrive, delayed dentition, alopecia and sclerodermatous skin changes. On average, death occurs at an age of 13 years. Most patients die from progressive atherosclerosis of the coronary and cerebrovascular arteries. Until Eriksson et al. (2003) reported the identification of disease causing mutations in the LMNA-gene, the prevailing hypothesis was that HGPS was a sporadic autosomal dominant disorder. The possibility of autosomal recessive inheritance led Eriksson et al. to perform a genome-wide scan searching for evidence of homozygosity. No evidence of homozygosity was identified but two HGPS samples showed uniparental isodisomy (UPD) of proximal chromosome 1q. This ultimately led to the identification of a predominant c.1824C>T mutation in the LMNA gene in 18/23 classical HGPS cases as well as two other mutations in two other HGPS patients. The c.1824C>T mutation turned out to affect splicing by creating a new splice donor site. Translation of the resulting mRNA produces a LMNA-A protein with an internal deletion (p.Val607_Gln656del) removing the internal proteolytic cleavage site which is used normally to remove the last 18 C-terminal amino acids to generate the mature LMNA protein (see also Mounkes et al.). The authors noted several cases where a cell line contained a secondary somatic mutation rescueing a deleterious change (twice a large deletion and once a somatic recombination).
• LDHPC; Lipoatrophy with diabetes, hepatic steatosis, hypertrophic cardiomyopathy and leukomelanodermic papules (OMIM: 608056). In a male LDHPC patient Caux et al. (2003) found a heterozygous change in exon 2 of the LMNA gene resulting in an p.Arg133Leu change in the dimerization rod domain of lamins A and C. Immunofluorescence analysis of cultured skin fibroblasts showed nuclear disorganization and abnormal distribution of A-type lamins.
• WRN; Werner's syndrome (OMIM: 277700) is a progeroid syndrome caused by mutations at the WRN helicase locus. Chen et al. (2003) screened 26/129 index patients with 'atypical' WRN, i.e. having a more severe phenotype and no mutations in the RECQL2 gene, for mutations in the LMNA-gene. Heterozygous changes in the LMNA-gene were detected in four cases.
• CCPS; Judge et al. (ASHG meeting 2003 in Los Angeles) reported a mutation in the LMNA gene in six patients of a four generation family with a novel dominant disorder, designated cardiocutaneous progeria syndrome (CCPS). Clinical manifestations involve premature aging (average age at death 36.5 years) including graying of hair, loss of fat, wrinkled skin, dysfunction of cardiac valves, and aggressive atherosclerosis involving the coronary, cerebral, and peripheral arterial systems. Additional manifestations include skin malignancy and nephrosclerosis. Genome-wide linkage analysis pointed at a region at 1q21.2, including the LMNA-gene.
• RD: Navarro et al. (2004) reported a mutation in LMNA in two families with restrictive dermopathy (RD), also called tight skin contracture syndrome (OMIM: 275210). RD is a rare disorder
  mainly characterized by intrauterine growth retardation, tight and rigid skin with erosions, prominent
  superficial vasculature and epidermal hyperkeratosis, facial features (small mouth, small pinched nose
  and micrognathia), sparse/absent eyelashes and eyebrows, mineralization defects of the skull, thin
  dysplastic clavicles, pulmonary hypoplasia, multiple joint contractures and an early neonatal lethal
  course. Liveborn children usually die within the first week of life.

Functionally tested variants

Mutations in the phosphoacceptor site (Ser22...) strongly interfere with lamina disassembly (Heald & McKeon 1990). Mutations in the two segments at either end of the ~45 kDa alpha-helical rod domain showed that these play a crucial role in in the assembly of IF-dimers into higher order oligomers (McCormick [1993], Stuurman [1996]).

The Arg482Gln mutation was tested by Holt et al. (2001) in transfected COS-cells; it did not affect the ability of lamin A to form a nuclear lamina or to interact with the nuclear membrane protein emerin. The consequences of changes in the lamin A/C sequence have also been studied by Brown CA et al. (ASHG-meeting 2002, abstract 2185, Am.J.Hum.Genet. 71: S542). Expression of an EGFP-lamin A fusion protein in mouse C2C12 or monkey COS7 cells showed;

• normal localisation for the changes Arg190dup, Arg527Pro, Leu530Pro, Arg541Ser and Gly602Ser
• mislocalisation for the changes Arg133Pro, Gln355del and Glu361Lys
• mislocalisation incl. of endogenous lamin C and emerin for the changes Thr150Pro, Glu358Lys and Arg453Trp

An increased number of irregular shaped fibroblast nuclei have been seen in combination with some LMNA mutations, e.g. Leu140Arg (419T>G) Chen [2003] causing atypical Werner's syndrome.

lamin A/C sequence variations (mutations and polymorphisms)

Animal models

By deleting exons 8-11, Sullivan et al. (1999) generated a LMNA knock-out mouse. The mice lack detectable lamins A/C and show a dystrophic condition related to EDMD, i.e. the appearance of skeletal and cardiac muscle alterations and perturbations of the nuclear envelope.

A mouse knock-out of the Zmpste24 metalloproteinase gene showed defective pre-lamin-A processing; homozygote mice show a phenotype resembling the clinical features observed in HPGS-patients (Mounkes et al.).

Miscellaneous

DNA-primers

RNA-primers

Legend:
Exonic sequences are in upper case, intronic and gene flanking sequences in lower case and added primer tails in italics. Amplified: region amplified (cDNA Reference Sequence). Length: length of PCR-product in basepairs. Reference: publication describing the primer(s). Forward primer: sequence of forward primer. Reverse primer: sequence of reverse primer. Name: name of the primers.

lamin A/C sequences

• cDNA-sequence
  • human
    • RefSeq - NM_170707 (lamin A), NM_005572 (lamin C), NM_170708 (laminAdel10)
    • cDNA Reference Sequence (used for mutation description)
    • AJ011098 at GenBank, copy at this site
  • other species
    • mouse - NM_019390 / D13181
    • rat - X66870 / X76297
    • chicken - X16879
    • X.laevis - X06345
• gene sequence
  • GenBank AC007227, AL135927, AL356734 (exon 2-end), L12399 (exon 1), L12400 (exon 2), L12401 (exon 3-12)
  • other species
    • mouse - D49732 (exon 1), D49734 (exon 2), D49735 (exon 3-5), D49733 (exon 6-12)
    • rat - Y15465
• protein sequences
  • human RefSeq - NP_005563 NP_733821 (lamin A), NP_005563 (lamin C), NP_733822 (laminAdel10)
  • other species
    • mouse - P48678
    • rat - P48679
    • chicken - P13648
    • [Danio rerio] - NP_694503
    • [Xenopus laevis] - P11048

similar sequences

• lamin B
  • human: B1 - NP_005564 / B2 - Q03252
  • mouse: B1 - NP_034851 / B2 - NP_034852
  • rat: B1 - NP_446357
  • chicken: B1 - P14731 / B2 - P14732
  • [Carassius auratus]: B2 - BAB32978 / B3 - BAB32977
  • [Danio rerio]: B1 - NP_694504 / B2 NP_571077 / L3 - NP_694505
• lamin
  • [Xenopus laevis]: LI - P09010 / LII - P21910 / LIII - S01301
  • [Drosophila melanogaster]: NP_476616 / C - NP_523742
• peripherin (PRPH) - NP_006253
• desmin (DES) - AAH32116
• internexin neuronal intermediate filament protein, alpha (INA) - NP_116116

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