The Xvex-1 antimorph reveals the temporal competence for organizer formation and an early role for ventral homeobox genes.
The organizer in vertebrate embryos has been shown to play a central role in their development by antagonizing ventralizing signals and promoting dorsal development. The ventral homeobox gene, Xvex-1, is capable of fulfilling some of the functions of BMP-4. By fusion to activation and repression domains, Xvex-1 was shown to function as a repressor of transcription. The activator version of Xvex-1, the antimorph, was made inducible by fusion to the ligand binding domain of the glucocorticoid receptor. The organizer genes, gsc and Otx-2, were identified as direct targets of Xvex-1. The XVEX-1 antimorph can induce the formation of secondary axes. Temporal analysis of secondary axis induction revealed that the competence to induce a secondary organizer ends with the onset of gastrulation. The same temporal competence window was exhibited by an inducible gsc construct. Partial loss of Xvex-1 activity was able to improve the efficiency of secondary axis induction by the dominant negative BMP receptor or Smad6. These observations together with the early widespread expression of Xvex-1 throughout the embryo prior to gastrulation encoding a homeodomain repressor protein, suggest that elements of the ventral signaling pathway play an important role during late blastula in restricting the formation of Spemann's organizer.
Shapira
E
E
Department of Cellular Biochemistry and Human Genetics, Faculty of Medicine, Hebrew University, P.O. Box 12272, Jerusalem, Israel.
Marom1
K
K
Levy
V
V
Yelin
R
R
Fainsod
A
A
D000818:Animals; D019677:Artificial Gene Fusion; D055415:Bone Morphogenetic Protein 4; D019485:Bone Morphogenetic Proteins / Q000235:genetics*; D004625:Embryo, Nonmammalian / Q000196:embryology; D018507:Gene Expression Regulation, Developmental; D018398:Homeodomain Proteins / Q000235:genetics*; D014981:Xenopus / Q000196:embryology* / Q000235:genetics*; D029867:Xenopus Proteins
D055415:Bone Morphogenetic Protein 4; D019485:Bone Morphogenetic Proteins; D018398:Homeodomain Proteins; D029867:Xenopus Proteins; C525812:bmp4 protein, Xenopus; C121962:ventx3.2 protein, Xenopus