Muscleblind isoforms are functionally distinct and regulate α -actinin splicing
Drosophila Muscleblind (Mbl) proteins control terminal muscle and neural differentiation, but their molecular function has not been experimentally addressed. Such an analysis is relevant as the human Muscleblind-like homologs (MBNL1–3) are implicated in the pathogenesis of the inherited muscular dev...
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Published in | Differentiation (London) Vol. 75; no. 5; pp. 427 - 440 |
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Main Authors | , , , , , , , |
Format | Journal Article |
Language | English |
Published |
Malden, USA
Elsevier B.V
01.06.2007
Blackwell Publishing Inc |
Subjects | |
Online Access | Get full text |
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Summary: | Drosophila Muscleblind (Mbl) proteins control terminal muscle and neural differentiation, but their molecular function has not been experimentally addressed. Such an analysis is relevant as the human Muscleblind-like homologs (MBNL1–3) are implicated in the pathogenesis of the inherited muscular developmental and degenerative disease myotonic dystrophy. The
Drosophila muscleblind gene expresses four protein coding splice forms (
mblA to
mblD) that are differentially expressed during the
Drosophila life cycle, and which vary markedly in their ability to rescue the embryonic lethal phenotype of
muscleblind mutant flies. Analysis of
muscleblind mutant embryos reveals misregulated alternative splicing of the transcripts encoding Z-band component α-Actinin, which can be replicated in human cells expressing a
Drosophila α
-actinin minigene and epitope-tagged Muscleblind isoforms. MblC appreciably altered α
-actinin splicing in this assay, whereas other isoforms had only a marginal or no effect, demonstrating functional specialization among Muscleblind proteins. To further analyze the molecular basis of these differences, we studied the subcellular localization of Muscleblind isoforms. Consistent with the splicing assay results, MblB and MblC were enriched in the nucleus while MblA was predominantly cytoplasmic. In myotonic dystrophy, transcripts bearing expanded non-coding CUG or CCUG repeats interfere with the function of human MBNL proteins. Co-expression of CUG repeat RNA with the α
-actinin minigene altered splicing compared with that seen in
muscleblind mutant embryos, indicating that CUG repeat expansion RNA also interferes with
Drosophila muscleblind function. Moreover MblA, B, and C co-localize with CUG repeat RNA in nuclear foci in cell culture. Our observations indicate that Muscleblind isoforms perform different functions
in vivo, that MblC controls
muscleblind-dependent alternative splicing events, and establish the functional conservation between Muscleblind and MBNL proteins both over a physiological target (α
-actinin) and a pathogenic one (CUG repeats). |
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Bibliography: | Present address: The Wellcome Trust Centre for Cell Biology, Michael Swann Building, Mayfield Road, Edinburgh EH9 3JR, U.K. * ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 |
ISSN: | 0301-4681 1432-0436 |
DOI: | 10.1111/j.1432-0436.2006.00156.x |