title: Transcription of the myogenic regulatory gene Mef2 in cardiac, somatic, and visceral muscle cell lineages is regulated by a Tinman-dependent core enhancer.
abstract: The MADS-box transcription factor MEF2 is expressed specifically in developing cardiac, somatic, and visceral muscle cell lineages during Drosophila embryogenesis and is required for myoblast differentiation and muscle morphogenesis. To define the mechanisms that regulate Mef2 transcription, we have analyzed the Mef2 upstream region for sequences sufficient to recapitulate the expression pattern of the gene in Drosophila embryos. Here we describe a complex enhancer located 5.8 kb upstream of the Drosophila Mef2 gene that controls transcription in cardial cells of the dorsal vessel, a subset of somatic muscle founder cells, and the visceral muscle cells. The core of this enhancer contains two evolutionarily conserved binding sites for the homeodomain protein Tinman (Tin), expressed in developing cardiac, somatic, and visceral muscle lineages. Both Tin binding sites are required for enhancer activity in all three muscle cell lineages. Whereas the 285-bp enhancer core alone is sufficient for expression in cardiac cells, expression in somatic founder cells and visceral muscle is dependent on the core enhancer plus unique flanking sequences that include an evolutionarily conserved E box. These results reveal an essential role for Tin in activation of Mef2 transcription in multiple myogenic lineages and demonstrate that transcriptional activity of Tin is dependent on combinatorial interactions with other factors unique to different muscle cell types.
authors.affiliation: Department of Molecular Biology, University of Texas Southwestern Medical Center at Dallas, 6000 Harry Hines Boulevard, Dallas, Texas 75235-9148, USA.
authors.forename: R M
authors.initials: RM
authors.lastname: Cripps
authors.forename: B
authors.initials: B
authors.lastname: Zhao
authors.forename: E N
authors.initials: EN
authors.lastname: Olson
mesh_terms: D000818:Animals; D005075:Biological Evolution; D004268:DNA-Binding Proteins / Q000235:genetics*; D004330:Drosophila / Q000196:embryology*; D029721:Drosophila Proteins; D004742:Enhancer Elements, Genetic; D018507:Gene Expression Regulation, Developmental; D018398:Homeodomain Proteins / Q000502:physiology*; D064326:MEF2 Transcription Factors; D009132:Muscles / Q000196:embryology*; D018006:Myogenic Regulatory Factors; D012097:Repressor Proteins / Q000502:physiology; D015534:Trans-Activators / Q000502:physiology; D014157:Transcription Factors / Q000235:genetics*; D014158:Transcription, Genetic
chemical_list: D004268:DNA-Binding Proteins; D029721:Drosophila Proteins; D018398:Homeodomain Proteins; D064326:MEF2 Transcription Factors; C499409:Mef2 protein, Drosophila; D018006:Myogenic Regulatory Factors; D012097:Repressor Proteins; D015534:Trans-Activators; D014157:Transcription Factors; C104163:bagpipe protein, Drosophila; C102933:tin protein, Drosophila