title: Wnt signaling and tbx16 form a bistable switch to commit bipotential progenitors to mesoderm.
abstract: Anterior to posterior growth of the vertebrate body is fueled by a posteriorly located population of bipotential neuro-mesodermal progenitor cells. These progenitors have a limited rate of proliferation and their maintenance is crucial for completion of the anterior-posterior axis. How they leave the progenitor state and commit to differentiation is largely unknown, in part because widespread modulation of factors essential for this process causes organism-wide effects. Using a novel assay, we show that zebrafish Tbx16 (Spadetail) is capable of advancing mesodermal differentiation cell-autonomously. Tbx16 locks cells into the mesodermal state by not only activating downstream mesodermal genes, but also by repressing bipotential progenitor genes, in part through a direct repression of sox2. We demonstrate that tbx16 is activated as cells move from an intermediate Wnt environment to a high Wnt environment, and show that Wnt signaling activates the tbx16 promoter. Importantly, high-level Wnt signaling is able to accelerate mesodermal differentiation cell-autonomously, just as we observe with Tbx16. Finally, because our assay for mesodermal commitment is quantitative we are able to show that the acceleration of mesodermal differentiation is surprisingly incomplete, implicating a potential separation of cell movement and differentiation during this process. Together, our data suggest a model in which high levels of Wnt signaling induce a transition to mesoderm by directly activating tbx16, which in turn acts to irreversibly flip a bistable switch, leading to maintenance of the mesodermal fate and repression of the bipotential progenitor state, even as cells leave the initial high-Wnt environment.
authors.affiliation: Department of Biochemistry, University of Washington, Seattle, WA 98195, USA.
authors.forename: Cortney M
authors.initials: CM
authors.lastname: Bouldin
authors.affiliation: Department of Biochemistry, University of Washington, Seattle, WA 98195, USA.
authors.forename: Alyssa J
authors.initials: AJ
authors.lastname: Manning
authors.affiliation: Department of Biochemistry, University of Washington, Seattle, WA 98195, USA.
authors.forename: Yu-Hsuan
authors.initials: YH
authors.lastname: Peng
authors.affiliation: Department of Biochemistry, University of Washington, Seattle, WA 98195, USA.
authors.forename: Gist H
authors.initials: GH
authors.lastname: Farr
authors.affiliation: Department of Biochemistry, University of Washington, Seattle, WA 98195, USA.
authors.forename: King L
authors.initials: KL
authors.lastname: Hung
authors.affiliation: Department of Biochemistry, University of Washington, Seattle, WA 98195, USA.
authors.forename: Alice
authors.initials: A
authors.lastname: Dong
authors.affiliation: Department of Biochemistry, University of Washington, Seattle, WA 98195, USA kimelman@uw.edu.
authors.forename: David
authors.initials: D
authors.lastname: Kimelman
mesh_terms: D000818:Animals; D019521:Body Patterning; D002454:Cell Differentiation; D019070:Cell Lineage; D002465:Cell Movement; D018507:Gene Expression Regulation, Developmental; D006360:Heat-Shock Proteins / Q000378:metabolism; D017403:In Situ Hybridization; D008648:Mesoderm / Q000378:metabolism*; D051379:Mice; D008856:Microscopy, Fluorescence; D009132:Muscles / Q000196:embryology / Q000378:metabolism; D009474:Neurons / Q000378:metabolism; D009841:Oligonucleotides / Q000737:chemistry; D011401:Promoter Regions, Genetic; D013234:Stem Cells / Q000166:cytology; D020825:T-Box Domain Proteins / Q000378:metabolism*; D019076:Transgenes; D060449:Wnt Signaling Pathway; D060509:Wnt3A Protein / Q000378:metabolism; D015027:Zebrafish; D029961:Zebrafish Proteins / Q000378:metabolism*
chemical_list: D006360:Heat-Shock Proteins; D009841:Oligonucleotides; D020825:T-Box Domain Proteins; D060509:Wnt3A Protein; C555512:Wnt3a protein, zebrafish; D029961:Zebrafish Proteins; C112539:tbx16 protein, zebrafish
keywords: Bipotential; Neuromesodermal; Somitogenesis; Spadetail; Tbx16; Wnt