title: Head formation: OTX2 regulates Dkk1 and Lhx1 activity in the anterior mesendoderm.
abstract: The Otx2 gene encodes a paired-type homeobox transcription factor that is essential for the induction and the patterning of the anterior structures in the mouse embryo. Otx2 knockout embryos fail to form a head. Whereas previous studies have shown that Otx2 is required in the anterior visceral endoderm and the anterior neuroectoderm for head formation, its role in the anterior mesendoderm (AME) has not been assessed specifically. Here, we show that tissue-specific ablation of Otx2 in the AME phenocopies the truncation of the embryonic head of the Otx2 null mutant. Expression of Dkk1 and Lhx1, two genes that are also essential for head formation, is disrupted in the AME of the conditional Otx2-deficient embryos. Consistent with the fact that Dkk1 is a direct target of OTX2, we showed that OTX2 can interact with the H1 regulatory region of Dkk1 to activate its expression. Cross-species comparative analysis, RT-qPCR, ChIP-qPCR and luciferase assays have revealed two conserved regions in the Lhx1 locus to which OTX2 can bind to activate Lhx1 expression. Abnormal development of the embryonic head in Otx2;Lhx1 and Otx2;Dkk1 compound mutant embryos highlights the functional intersection of Otx2, Dkk1 and Lhx1 in the AME for head formation.
authors.affiliation: Embryology Unit, Children's Medical Research Institute, Locked Bag 23, Wentworthville, New South Wales 2145, Australia Discipline of Medicine, Sydney Medical School, University of Sydney, New South Wales 2006, Australia.
authors.forename: Chi Kin
authors.initials: CK
authors.lastname: Ip
authors.affiliation: Embryology Unit, Children's Medical Research Institute, Locked Bag 23, Wentworthville, New South Wales 2145, Australia Discipline of Medicine, Sydney Medical School, University of Sydney, New South Wales 2006, Australia nfossat@cmri.org.au.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Fossat
authors.affiliation: Embryology Unit, Children's Medical Research Institute, Locked Bag 23, Wentworthville, New South Wales 2145, Australia.
authors.forename: Vanessa
authors.initials: V
authors.lastname: Jones
authors.affiliation: Equipe Neurodéveloppement, Institut de Biologie Valrose, UMR UNS/CNRS 7277/INSERM 1091, Université Nice Sophia Antipolis, Parc Valrose, 06108 Nice cedex 2, France.
authors.forename: Thomas
authors.initials: T
authors.lastname: Lamonerie
authors.affiliation: Embryology Unit, Children's Medical Research Institute, Locked Bag 23, Wentworthville, New South Wales 2145, Australia Discipline of Medicine, Sydney Medical School, University of Sydney, New South Wales 2006, Australia.
authors.forename: Patrick P L
authors.initials: PP
authors.lastname: Tam
mesh_terms: D016475:3T3 Cells; D000818:Animals; D003433:Crosses, Genetic; D018507:Gene Expression Regulation, Developmental; D006257:Head / Q000196:embryology*; D036341:Intercellular Signaling Peptides and Proteins / Q000378:metabolism*; D060850:LIM-Homeodomain Proteins / Q000378:metabolism*; D008156:Luciferases / Q000378:metabolism; D008648:Mesoderm / Q000502:physiology*; D051379:Mice; D009154:Mutation; D051857:Otx Transcription Factors / Q000502:physiology*; D010641:Phenotype; D014157:Transcription Factors / Q000378:metabolism*
chemical_list: C501127:Dkk1 protein, mouse; D036341:Intercellular Signaling Peptides and Proteins; D060850:LIM-Homeodomain Proteins; C499523:Lhx1 protein, mouse; D051857:Otx Transcription Factors; C497660:Otx2 protein, mouse; D014157:Transcription Factors; D008156:Luciferases
keywords: Anterior mesendoderm; Dkk1; Head formation; Lhx1; Mouse; Otx2