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Tissue-specific gene activation by MyoD: determination of specificity by cis-acting repression elements
H Weintraub1, T Genetta, T Kadesch
1Hutchinson Cancer Center, Howard Hughes Medical Institute, Seattle, Washington 98104.
Genes & Development
|September 15, 1994
Summary
MyoD and E12 are transcription factors that bind DNA similarly. A negative element in the IgH enhancer represses MyoD, explaining its muscle-specific gene activation.
Area of Science:
- Molecular Biology
- Genetics
- Biochemistry
Background:
- MyoD and E12 are basic helix-loop-helix (bHLH) transcription factors.
- They bind to similar E-box sequences (CANNTG) in DNA.
- MyoD is muscle-specific, while E12 is a B-cell activator.
Purpose of the Study:
- Investigate the mechanism of enhancer specificity for MyoD and E12.
- Determine why MyoD activates muscle genes but not non-muscle genes like IgH.
Main Methods:
- Analysis of immunoglobulin heavy chain (IgH) and muscle creatine kinase (MCK) enhancers.
- Reporter gene assays to measure enhancer activity.
- Site-directed mutagenesis to identify regulatory elements.
Main Results:
- IgH enhancer is activated by E12 but repressed by MyoD.
- MCK enhancer is strongly activated by MyoD but not E12.
- A cis-acting negative element within the IgH enhancer specifically represses MyoD activity via its bHLH region.
Conclusions:
- The IgH enhancer contains a MyoD-specific negative element crucial for its repression.
- This negative element's flanking sequences determine specificity, not just the E-box.
- MyoD's exclusive activation of myogenic genes is due to negative elements in non-muscle enhancers preventing its activity.