E-box- and MEF-2-independent muscle-specific expression, positive autoregulation, and cross-activation of the chicken MyoD (CMD1) promoter reveal an indirect regulatory pathway.
Members of the MyoD family of gene-regulatory proteins (MyoD, myogenin, myf5, and MRF4) have all been shown not only to regulate the transcription of numerous muscle-specific genes but also to positively autoregulate and cross activate each other's transcription. In the case of muscle-specific genes, this transcriptional regulation can often be correlated with the presence of a DNA consensus in the regulatory region CANNTG, known as an E box. Little is known about the regulatory interactions of the myogenic factors themselves; however, these interactions are thought to be important for the activation and maintenance of the muscle phenotype. We have identified the minimal region in the chicken MyoD (CMD1) promoter necessary for muscle-specific transcription in primary cultures of embryonic chicken skeletal muscle. The CMD1 promoter is silent in primary chick fibroblast cultures and in muscle cell cultures treated with the thymidine analog bromodeoxyuridine. However, CMD1 and chicken myogenin, as well as, to a lesser degree, chicken Myf5 and MRF4, expressed in trans can activate transcription from the minimal CMD1 promoter in these primary fibroblast cultures. Here we show that the CMD1 promoter contains numerous E-box binding sites for CMD1 and the other myogenic factors, as well as a MEF-2 binding site. Surprisingly, neither muscle-specific and the other myogenic factors, as well as a MEF-2 binding site. Surprisingly, neither muscle-specific expression, autoregulation, or cross activation depends upon the presence of of these E-box or MEF-2 binding sites in the CMD1 promoter. These results demonstrate that the autoregulation and cross activation of the chicken MyoD promoter through the putative direct binding of the myogenic basic helix-loop-helix regulatory factors is mediated through an indirect pathway that involves unidentified regulatory elements and/or ancillary factors.
Dechesne
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CA
Laboratory of Biochemistry, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892.
Wei
Q
Q
Eldridge
J
J
Gannoun-Zaki
L
L
Millasseau
P
P
Bougueleret
L
L
Caterina
D
D
Paterson
B M
BM
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D002645:Chickens; D003001:Cloning, Molecular; D004268:DNA-Binding Proteins / Q000378:metabolism; D005786:Gene Expression Regulation; D005796:Genes; D018257:Helix-Loop-Helix Motifs; D064326:MEF2 Transcription Factors; D008969:Molecular Sequence Data; D009124:Muscle Proteins / Q000502:physiology; D009132:Muscles / Q000502:physiology*; D017570:MyoD Protein / Q000235:genetics*; D051787:Myogenic Regulatory Factor 5; D018006:Myogenic Regulatory Factors / Q000502:physiology; D018008:Myogenin / Q000502:physiology; D011401:Promoter Regions, Genetic; D015534:Trans-Activators; D014157:Transcription Factors / Q000378:metabolism
D004268:DNA-Binding Proteins; D064326:MEF2 Transcription Factors; D009124:Muscle Proteins; D017570:MyoD Protein; D051787:Myogenic Regulatory Factor 5; D018006:Myogenic Regulatory Factors; D018008:Myogenin; D015534:Trans-Activators; D014157:Transcription Factors; C063403:myogenic factor 6