Tissue-specific splicing of a ubiquitously expressed transcription factor is essential for muscle differentiation
- Soji Sebastian1,
- Hervé Faralli1,4,
- Zizhen Yao2,4,
- Patricia Rakopoulos1,3,
- Carmen Palii1,
- Yi Cao2,
- Kulwant Singh1,
- Qi-Cai Liu1,
- Alphonse Chu1,
- Arif Aziz1,
- Marjorie Brand1,3,
- Stephen J. Tapscott2 and
- F. Jeffrey Dilworth1,3,5
- 1Sprott Center for Stem Cell Research, Ottawa Hospital Research Institute, Ottawa, Ontario K1H 8L6, Canada,;
- 2Human Biology Division, Fred Hutchinson Cancer Research Center, Seattle, Washington 98109, USA;
- 3Department of Cellular and Molecular Medicine, University of Ottawa, Ontario K1H 8L6, Canada
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↵4 These authors contributed equally to this work.
Abstract
Alternate splicing contributes extensively to cellular complexity by generating protein isoforms with divergent functions. However, the role of alternate isoforms in development remains poorly understood. Mef2 transcription factors are essential transducers of cell signaling that modulate differentiation of many cell types. Among Mef2 family members, Mef2D is unique, as it undergoes tissue-specific splicing to generate a muscle-specific isoform. Since the ubiquitously expressed (Mef2Dα1) and muscle-specific (Mef2Dα2) isoforms of Mef2D are both expressed in muscle, we examined the relative contribution of each Mef2D isoform to differentiation. Using both in vitro and in vivo models, we demonstrate that Mef2D isoforms act antagonistically to modulate differentiation. While chromatin immunoprecipitation (ChIP) sequencing analysis shows that the Mef2D isoforms bind an overlapping set of genes, only Mef2Dα2 activates late muscle transcription. Mechanistically, the differential ability of Mef2D isoforms to activate transcription depends on their susceptibility to phosphorylation by protein kinase A (PKA). Phosphorylation of Mef2Dα1 by PKA provokes its association with corepressors. Conversely, exon switching allows Mef2Dα2 to escape this inhibitory phosphorylation, permitting recruitment of Ash2L for transactivation of muscle genes. Thus, our results reveal a novel mechanism in which a tissue-specific alternate splicing event has evolved that permits a ubiquitously expressed transcription factor to escape inhibitory signaling for temporal regulation of gene expression.
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Footnotes
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↵5 Corresponding author
E-mail jdilworth{at}ohri.ca
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Supplemental material is available for this article.
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Article published online ahead of print. Article and publication date are online at http://www.genesdev.org/cgi/doi/10.1101/gad.215400.113.
- Received February 4, 2013.
- Accepted April 26, 2013.
- Copyright © 2013 by Cold Spring Harbor Laboratory Press
Freely available online through the Genes & Development Open Access option.