title: Wnt3a signal pathways activate MyoD expression by targeting cis-elements inside and outside its distal enhancer.
abstract: Wnt proteins are secreted cytokines and several Wnts are expressed in the developing somites and surrounding tissues. Without proper Wnt stimulation, the organization of the dermomyotome and myotome can become defective. These Wnt signals received by somitic cells can lead to activation of Pax3/Pax7 and myogenic regulatory factors (MRFs), especially Myf5 and MyoD. However, it is currently unknown whether Wnts activate Myf5 and MyoD through direct targeting of their cis-regulatory elements or via indirect pathways. To clarify this issue, in the present study, we tested the regulation of MyoD cis-regulatory elements by Wnt3a secreted from human embryonic kidney (HEK)-293T cells. We found that Wnt3a activated the MyoD proximal 6.0k promoter (P6P) only marginally, but highly enhanced the activity of the composite P6P plus distal enhancer (DE) reporter through canonical and non-canonical pathways. Further screening of the intervening fragments between the DE and the P6P identified a strong Wnt-response element (WRE) in the upstream -8 to -9k region (L fragment) that acted independently of the DE, but was dependent on the P6P. Deletion of a Pax3/Pax7-targeted site in the L fragment significantly reduced its response to Wnt3a, implying that Wnt3a activates the L fragment partially through Pax3/Pax7 action. Binding of β-catenin and Pax7 to their target sites in the DE and the L fragment respectively was also demonstrated by ChIP. These observations demonstrated the first time that Wnt3a can directly activate MyoD expression through targeting cis-elements in the DE and the L fragment.
authors: *Department of Life Sciences, National Central University, 300 Jhongda Road, Jhongli 32001, Taiwan.
authors: Yu Chih
authors: YC
authors: Pan
authors: *Department of Life Sciences, National Central University, 300 Jhongda Road, Jhongli 32001, Taiwan.
authors: Xiao Wen
authors: XW
authors: Wang
authors: *Department of Life Sciences, National Central University, 300 Jhongda Road, Jhongli 32001, Taiwan.
authors: Han Feng
authors: HF
authors: Teng
authors: *Department of Life Sciences, National Central University, 300 Jhongda Road, Jhongli 32001, Taiwan.
authors: Yi Ju
authors: YJ
authors: Wu
authors: *Department of Life Sciences, National Central University, 300 Jhongda Road, Jhongli 32001, Taiwan.
authors: Hsuan Chia
authors: HC
authors: Chang
authors: *Department of Life Sciences, National Central University, 300 Jhongda Road, Jhongli 32001, Taiwan.
authors: Shen Liang
authors: SL
authors: Chen
mesh_terms: D002460:Cell Line; D005786:Gene Expression Regulation / Q000502:physiology*; D006801:Humans; D017570:MyoD Protein / Q000096:biosynthesis* / Q000235:genetics; D051787:Myogenic Regulatory Factor 5 / Q000235:genetics / Q000378:metabolism; D000072041:PAX3 Transcription Factor; D051763:PAX7 Transcription Factor / Q000235:genetics / Q000378:metabolism; D051761:Paired Box Transcription Factors / Q000235:genetics / Q000378:metabolism; D020218:Response Elements / Q000502:physiology*; D060449:Wnt Signaling Pathway / Q000502:physiology*; D060509:Wnt3A Protein / Q000235:genetics / Q000378:metabolism*
chemical_list: C497417:MYF5 protein, human; D017570:MyoD Protein; C057363:MyoD1 myogenic differentiation protein; D051787:Myogenic Regulatory Factor 5; D000072041:PAX3 Transcription Factor; C489409:PAX3 protein, human; D051763:PAX7 Transcription Factor; C497321:PAX7 protein, human; D051761:Paired Box Transcription Factors; C555510:WNT3A protein, human; D060509:Wnt3A Protein
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