Expression and localization of nuclear proteins in autosomal-dominant Emery-Dreifuss muscular dystrophy with LMNA R377H mutation.
BACKGROUND
The autosomal dominant form of Emery-Dreifuss muscular dystrophy (AD-EDMD) is caused by mutations in the gene encoding for the lamins A and C (LMNA). Lamins are intermediate filament proteins which form the nuclear lamina underlying the inner nuclear membrane. We have studied the expression and the localization of nuclear envelope proteins in three different cell types and muscle tissue of an AD-EDMD patient carrying a point mutation R377H in the lamin A/C gene.


RESULTS
Lymphoblastoid cells, skin fibroblasts, primary myoblasts and muscle thin sections were studied by immunocytochemistry and electron microscopy. Cellular levels of A-type lamins were reduced compared to control cells. In contrast, the amount of emerin and lamin B appeared unaltered. Cell synchronization experiments showed that the reduction of the cellular level of A-type lamin was due to instability of lamin A. By electron microscopy, we identified a proportion of nuclei with morphological alterations in lymphoblastoid cells, fibroblasts and mature muscle fibres. Immunofluorescence microscopy showed that a major population of the lamin B receptor (LBR), an inner nuclear membrane protein, was recovered in the cytoplasm in association with the ER. In addition, the intranuclear organization of the active form of RNA polymerase II was markedly different in cells of this AD-EDMD patient. This aberrant intranuclear distribution was specifically observed in muscle cells where the pathology of EDMD predominates.


CONCLUSIONS
From our results we conclude: Firstly, that structural alterations of the nuclei which are found only in a minor fraction of lymphoblastoid cells and mature muscle fibres are not sufficient to explain the clinical pathology of EDMD; Secondly, that wild type lamin A is required not only for the retention of LBR in the inner nuclear membrane but also for a correct localization of the transcriptionally active RNA pol II in muscle cells. We speculate that a rearrangement of the internal chromatin could lead to muscle-specific disease symptoms by interference with proper mRNA transcription.
Reichart
Beate
B
Department of Cell and Developmental Biology, University of Würzburg, Germany. beatereichart@web.de
Klafke
Ruth
R
Dreger
Christine
C
Krüger
Eleonora
E
Motsch
Isabell
I
Ewald
Andrea
A
Schäfer
Jochen
J
Reichmann
Heinz
H
Müller
Clemens R
CR
Dabauvalle
Marie-Christine
MC
D019943:Amino Acid Substitution; D002467:Cell Nucleus / Q000737:chemistry / Q000648:ultrastructure; D002843:Chromatin / Q000648:ultrastructure; D006801:Humans; D034904:Lamin Type A / Q000235:genetics* / Q000378:metabolism; D020389:Muscular Dystrophy, Emery-Dreifuss / Q000235:genetics* / Q000378:metabolism* / Q000473:pathology; D032446:Myoblasts / Q000737:chemistry / Q000166:cytology; D009685:Nuclear Envelope / Q000648:ultrastructure; D009687:Nuclear Proteins / Q000032:analysis* / Q000378:metabolism*; D017354:Point Mutation; D012319:RNA Polymerase II / Q000032:analysis; D018160:Receptors, Cytoplasmic and Nuclear / Q000032:analysis; D000097682:Lamin B Receptor
D002843:Chromatin; D034904:Lamin Type A; D009687:Nuclear Proteins; D012319:RNA Polymerase II; D018160:Receptors, Cytoplasmic and Nuclear; D000097682:Lamin B Receptor