title: Pbx homeodomain proteins direct Myod activity to promote fast-muscle differentiation.
abstract: The basic helix-loop-helix (bHLH) transcription factor Myod directly regulates gene expression throughout the program of skeletal muscle differentiation. It is not known how a Myod-driven myogenic program is modulated to achieve muscle fiber-type-specific gene expression. Pbx homeodomain proteins mark promoters of a subset of Myod target genes, including myogenin (Myog); thus, Pbx proteins might modulate the program of myogenesis driven by Myod. By inhibiting Pbx function in zebrafish embryos, we show that Pbx proteins are required in order for Myod to induce the expression of a subset of muscle genes in the somites. In the absence of Pbx function, expression of myog and of fast-muscle genes is inhibited, whereas slow-muscle gene expression appears normal. By knocking down Pbx or Myod function in combination with another bHLH myogenic factor, Myf5, we show that Pbx is required for Myod to regulate fast-muscle, but not slow-muscle, development. Furthermore, we show that Sonic hedgehog requires Myod in order to induce both fast- and slow-muscle markers but requires Pbx only to induce fast-muscle markers. Our results reveal that Pbx proteins modulate Myod activity to drive fast-muscle gene expression, thus showing that homeodomain proteins can direct bHLH proteins to establish a specific cell-type identity.
authors: Division of Human Biology, Fred Hutchinson Cancer Research Center, Seattle, Washington 98109, USA. lmaves@fhcrc.org
authors: Lisa
authors: L
authors: Maves
authors: Andrew Jan
authors: AJ
authors: Waskiewicz
authors: Biswajit
authors: B
authors: Paul
authors: Yi
authors: Y
authors: Cao
authors: Ashlee
authors: A
authors: Tyler
authors: Cecilia B
authors: CB
authors: Moens
authors: Stephen J
authors: SJ
authors: Tapscott
mesh_terms: D000818:Animals; D015870:Gene Expression; D018507:Gene Expression Regulation, Developmental; D053823:Hedgehog Proteins / Q000235:genetics / Q000378:metabolism; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism*; D024510:Muscle Development / Q000235:genetics*; D018482:Muscle, Skeletal / Q000196:embryology* / Q000378:metabolism; D017570:MyoD Protein / Q000235:genetics / Q000378:metabolism*; D018008:Myogenin / Q000378:metabolism; D020411:Oligonucleotide Array Sequence Analysis; D012333:RNA, Messenger / Q000032:analysis / Q000378:metabolism; D015027:Zebrafish / Q000196:embryology / Q000235:genetics; D029961:Zebrafish Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D053823:Hedgehog Proteins; D018398:Homeodomain Proteins; D017570:MyoD Protein; D018008:Myogenin; D012333:RNA, Messenger; D029961:Zebrafish Proteins