Nesprins: tissue-specific expression of epsilon and other short isoforms.
Nesprin-1-giant and nesprin-2-giant regulate nuclear positioning by the interaction of their C-terminal KASH domains with nuclear membrane SUN proteins and their N-terminal calponin-homology domains with cytoskeletal actin. A number of short isoforms lacking the actin-binding domains are produced by internal promotion. We have evaluated the significance of these shorter isoforms using quantitative RT-PCR and western blotting with site-specific monoclonal antibodies. Within a complete map of nesprin isoforms, we describe two novel nesprin-2 epsilon isoforms for the first time. Epsilon isoforms are similar in size and structure to nesprin-1-alpha. Expression of nesprin isoforms was highly tissue-dependent. Nesprin-2-epsilon-1 was found in early embryonic cells, while nesprin-2-epsilon-2 was present in heart and other adult tissues, but not skeletal muscle. Some cell lines lack shorter isoforms and express only one of the two nesprin genes, suggesting that either of the giant nesprins is sufficient for basic cell functions. For the first time, localisation of endogenous nesprin away from the nuclear membrane was shown in cells where removal of the KASH domain by alternative splicing occurs. By distinguishing between degradation products and true isoforms on western blots, it was found that previously-described beta and gamma isoforms are expressed either at only low levels or with a limited tissue distribution. Two of the shortest alpha isoforms, nesprin-1-alpha-2 and nesprin-2-alpha-1, were found almost exclusively in cardiac and skeletal muscle and a highly conserved and alternatively-spliced exon, available in both nesprin genes, was always included in these tissues. These "muscle-specific" isoforms are thought to form a complex with emerin and lamin A/C at the inner nuclear membrane and mutations in all three proteins cause Emery-Dreifuss muscular dystrophy and/or inherited dilated cardiomyopathy, disorders in which only skeletal muscle and/or heart are affected.
Wolfson Centre for Inherited Neuromuscular Disease, RJAH Orthopaedic Hospital, Oswestry, United Kingdom; Institute of Genome Research (IGR), Vietnam Academy of Science and Technology (VAST), Hanoi, Vietnam.
Nguyen Thuy
NT
Duong
Wolfson Centre for Inherited Neuromuscular Disease, RJAH Orthopaedic Hospital, Oswestry, United Kingdom; Institute for Science and Technology in Medicine, Keele University, Staffordshire, United Kingdom.
Glenn E
GE
Morris
Wolfson Centre for Inherited Neuromuscular Disease, RJAH Orthopaedic Hospital, Oswestry, United Kingdom.
Le Thanh
le T
Lam
Cardiovascular Division, James Black Centre, King's College, London, United Kingdom.
Qiuping
Q
Zhang
Wolfson Centre for Inherited Neuromuscular Disease, RJAH Orthopaedic Hospital, Oswestry, United Kingdom; Dubowitz Neuromuscular Centre, Institute for Child Health and Great Ormond Street Hospital, London, United Kingdom.
Caroline A
CA
Sewry
Cardiovascular Division, James Black Centre, King's College, London, United Kingdom.
Catherine M
CM
Shanahan
Wolfson Centre for Inherited Neuromuscular Disease, RJAH Orthopaedic Hospital, Oswestry, United Kingdom; Institute for Science and Technology in Medicine, Keele University, Staffordshire, United Kingdom.
Ian
I
Holt
D017398:Alternative Splicing / Q000235:genetics; D000595:Amino Acid Sequence; D002460:Cell Line; D017124:Conserved Sequence / Q000235:genetics; D003598:Cytoskeletal Proteins; D018076:DNA, Complementary / Q000235:genetics; D053595:Embryonic Stem Cells / Q000378:metabolism; D005091:Exons / Q000235:genetics; D020869:Gene Expression Profiling; D006801:Humans; D008840:Microfilament Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D008969:Molecular Sequence Data; D018482:Muscle, Skeletal / Q000378:metabolism; D020389:Muscular Dystrophy, Emery-Dreifuss / Q000235:genetics; D009206:Myocardium / Q000378:metabolism; D009419:Nerve Tissue Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D009687:Nuclear Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D009928:Organ Specificity / Q000235:genetics*; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D017434:Protein Structure, Tertiary; D059748:Proteolysis; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D013154:Spleen / Q000378:metabolism
D003598:Cytoskeletal Proteins; D018076:DNA, Complementary; D008840:Microfilament Proteins; D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; D020033:Protein Isoforms; D012333:RNA, Messenger; C415465:SYNE1 protein, human; C485904:SYNE2 protein, human