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A new myocyte-specific enhancer-binding factor that recognizes a conserved element associated with multiple
L A Gossett1, D J Kelvin, E A Sternberg
1Department of Biochemistry and Molecular Biology, University of Texas, M.D. Anderson Cancer Center, Houston 77030.
Molecular and Cellular Biology
|November 1, 1989
Summary
Muscle creatine kinase (mck) gene activation during muscle cell differentiation is mediated by a novel myocyte-specific enhancer-binding factor, MEF-2. This factor appears early in differentiation and is suppressed by growth factors, suggesting its role in coordinating muscle gene expression.
Area of Science:
- Molecular Biology
- Cellular Differentiation
- Gene Regulation
Background:
- Skeletal myoblasts activate muscle-specific genes, including muscle creatine kinase (mck), when exposed to growth factor-deficient medium.
- A muscle-specific enhancer between base pairs -1350 and -1048 of the mck gene is crucial for its tissue specificity, developmental regulation, and high-level expression.
Purpose of the Study:
- To define regulatory mechanisms controlling the selective activation of the mck enhancer in differentiating muscle cells.
- To identify and characterize nuclear factors interacting with the mck enhancer region.
Main Methods:
- Deletion mutagenesis to delimit enhancer boundaries.
- Gel retardation assays, DNase I footprinting, and diethyl pyrocarbonate interference to analyze nuclear factor interactions.
- Analysis of nuclear extracts from various myogenic and nonmyogenic cell types at different differentiation stages.
Main Results:
- A region between 1,204 and 1,095 bp upstream of mck acts as a weak muscle-specific enhancer, dependent on an adjacent element for strong activity.
- A myocyte-specific enhancer-binding factor, designated MEF-2, recognizes a conserved A+T-rich sequence within this region.
- MEF-2 is undetectable in myoblasts and nonmyogenic cells but appears rapidly upon differentiation, requiring protein synthesis and suppressed by growth factors.
Conclusions:
- MEF-2 is a novel, myocyte-specific transcription factor expressed early in muscle differentiation.
- MEF-2 binding sites are conserved across multiple muscle-specific genes, suggesting its role in the coordinate regulation of myogenesis.
- The appearance of MEF-2 is regulated by growth factor signaling pathways that inhibit muscle-specific gene induction.