title: The pitx2 homeobox protein is required early for endoderm formation and nodal signaling. .
abstract: Nodal and Nodal-related factors play fundamental roles in a number of developmental processes,   including mesoderm and endoderm formation, patterning of the anterior neural plate, and determination   of bilateral asymmetry in vertebrates. pitx2, a paired-like homeobox gene, has been proposed to act   downstream of Nodal in the gene cascade providing left-right cues to the developing organs. Here, we   report that pitx2 is required early in the Nodal signaling pathway for specification of the endodermal and   mesodermal germ layers. We found that pitx2 is expressed very early during Xenopus and zebrafish   development and in many regions where Nodal signaling is required, including the presumptive   mesoderm and endoderm at the blastula and gastrula stages and the prechordal mesoderm at later   stages. In Xenopus embryos, overexpression of pitx2 caused ectopic expression of goosecoid and   sox-17 and interfered with mesoderm formation. Overexpression of pitx2 in Xenopus animal cap   explants partially mimics the effects of Nodal overexpression, suggesting that pitx2 is a mediator of   Nodal signaling during specification of the endoderm and prechordal plate, but not during mesoderm   induction. We further demonstrate that pitx2 is induced by Nodal signaling in Xenopus animal caps and   that the early expression of zebrafish pitx2 is absent when the Nodal signaling pathway is inactive.   Inhibition of pitx2 function using a chimeric EnR-pitx2 blocked specification of the mesoderm and   endoderm and caused severe embryonic defects resembling those seen when Nodal signaling is   inhibited. Following inhibition of pitx2 function, the fate of ventral vegetal blastomeres was shifted from   an endodermal to a more mesodermal fate, an effect that was reversed by wild-type pitx2. Finally, we   show that inhibition of pitx2 function interferes with the response of cells to Nodal signaling. Our results   provide direct evidence that pitx2 function is required for normal specification of the endodermal and   mesodermal germ layers.
authors.affiliation: Observatoire Oceanologique, UMR 7009 CNRS, Université de Paris   VI, 06230, Villefranche-sur-Mer, France.
authors.forename: M
authors.initials: M
authors.lastname: Faucourt
authors.forename: E
authors.initials: E
authors.lastname: Houliston
authors.forename: L
authors.initials: L
authors.lastname: Besnardeau
authors.forename: D
authors.initials: D
authors.lastname: Kimelman
authors.forename: T
authors.initials: T
authors.lastname: Lepage
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D003001:Cloning, Molecular; D004625:Embryo, Nonmammalian / Q000502:physiology*; D004707:Endoderm / Q000502:physiology*; D005775:Gastrula / Q000502:physiology*; D018507:Gene Expression Regulation, Developmental / Q000502:physiology*; D006657:Histones / Q000235:genetics; D018398:Homeodomain Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D008969:Molecular Sequence Data; D055457:Nodal Protein; D009687:Nuclear Proteins; D016366:Open Reading Frames; D051761:Paired Box Transcription Factors; D011994:Recombinant Proteins / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction / Q000502:physiology*; D014157:Transcription Factors / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D014158:Transcription, Genetic; D016212:Transforming Growth Factor beta / Q000235:genetics / Q000502:physiology*; D014714:Vertebrates; D014981:Xenopus / Q000196:embryology; D015027:Zebrafish / Q000196:embryology; D015053:Zygote / Q000502:physiology; D000097577:Homeobox Protein PITX2
chemical_list: D006657:Histones; D018398:Homeodomain Proteins; D055457:Nodal Protein; D009687:Nuclear Proteins; D051761:Paired Box Transcription Factors; D011994:Recombinant Proteins; D014157:Transcription Factors; D016212:Transforming Growth Factor beta; D000097577:Homeobox Protein PITX2; C101485:homeobox protein PITX1; C433629:homeobox protein PITX3