title: Brachyury establishes the embryonic mesodermal progenitor niche.
abstract: Formation of the early vertebrate embryo depends on a Brachyury/Wnt autoregulatory loop within the posterior mesodermal progenitors. We show that exogenous retinoic acid (RA), which dramatically truncates the embryo, represses expression of the zebrafish brachyury ortholog no tail (ntl), causing a failure to sustain the loop. We found that Ntl functions normally to protect the autoregulatory loop from endogenous RA by directly activating cyp26a1 expression. Thus, the embryonic mesodermal progenitors uniquely establish their own niche--with Brachyury being essential for creating a domain of high Wnt and low RA signaling--rather than having a niche created by separate support cells.
authors.affiliation: Department of Biochemistry, University of Washington, Seattle, Washington 98195, USA.
authors.forename: Benjamin L
authors.initials: BL
authors.lastname: Martin
authors.forename: David
authors.initials: D
authors.lastname: Kimelman
mesh_terms: D000818:Animals; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D047108:Embryonic Development; D053595:Embryonic Stem Cells / Q000378:metabolism*; D025461:Feedback, Physiological; D005326:Fetal Proteins / Q000502:physiology*; D008648:Mesoderm / Q000166:cytology*; D000072516:Retinoic Acid 4-Hydroxylase; D055153:Stem Cell Niche / Q000166:cytology / Q000378:metabolism*; D020825:T-Box Domain Proteins / Q000502:physiology*; D014212:Tretinoin / Q000494:pharmacology; D051153:Wnt Proteins / Q000378:metabolism; D015027:Zebrafish; D029961:Zebrafish Proteins; D000098908:Brachyury Protein
chemical_list: D003577:Cytochrome P-450 Enzyme System; D005326:Fetal Proteins; D000072516:Retinoic Acid 4-Hydroxylase; D020825:T-Box Domain Proteins; D014212:Tretinoin; D051153:Wnt Proteins; D029961:Zebrafish Proteins; D000098908:Brachyury Protein; C000607085:cyp26a1 protein, zebrafish