title: Early asymmetric cues triggering the dorsal/ventral gene regulatory network of the sea urchin embryo.
abstract: Dorsal/ventral (DV) patterning of the sea urchin embryo relies on a ventrally-localized organizer expressing Nodal, a pivotal regulator of the DV gene regulatory network. However, the inceptive mechanisms imposing the symmetry-breaking are incompletely understood. In Paracentrotus lividus, the Hbox12 homeodomain-containing repressor is expressed by prospective dorsal cells, spatially facing and preceding the onset of nodal transcription. We report that Hbox12 misexpression provokes DV abnormalities, attenuating nodal and nodal-dependent transcription. Reciprocally, impairing hbox12 function disrupts DV polarity by allowing ectopic expression of nodal. Clonal loss-of-function, inflicted by blastomere transplantation or gene-transfer assays, highlights that DV polarization requires Hbox12 action in dorsal cells. Remarkably, the localized knock-down of nodal restores DV polarity of embryos lacking hbox12 function. Finally, we show that hbox12 is a dorsal-specific negative modulator of the p38-MAPK activity, which is required for nodal expression. Altogether, our results suggest that Hbox12 function is essential for proper positioning of the DV organizer.
authors.affiliation: Department of Biological, Chemical and Pharmaceutical Sciences and Technologies, University of Palermo, Palermo, Italy.
authors.forename: Vincenzo
authors.initials: V
authors.lastname: Cavalieri
authors.affiliation: Department of Biological, Chemical and Pharmaceutical Sciences and Technologies, University of Palermo, Palermo, Italy.
authors.forename: Giovanni
authors.initials: G
authors.lastname: Spinelli
mesh_terms: D000818:Animals; D030801:Animals, Genetically Modified; D019521:Body Patterning / Q000235:genetics*; D016764:Cell Polarity; D003463:Cues; D004475:Ectoderm / Q000166:cytology; D004625:Embryo, Nonmammalian / Q000378:metabolism*; D047108:Embryonic Development / Q000235:genetics; D018507:Gene Expression Regulation, Developmental; D055785:Gene Knockdown Techniques; D053263:Gene Regulatory Networks; D018398:Homeodomain Proteins / Q000378:metabolism; D008954:Models, Biological; D009024:Morphogenesis / Q000235:genetics; D055457:Nodal Protein / Q000235:genetics / Q000378:metabolism; D047328:Paracentrotus / Q000196:embryology* / Q000235:genetics*; D012097:Repressor Proteins / Q000378:metabolism; D014158:Transcription, Genetic; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
chemical_list: D018398:Homeodomain Proteins; D055457:Nodal Protein; D012097:Repressor Proteins; D048051:p38 Mitogen-Activated Protein Kinases
keywords: cell biology; developmental biology; dorsal/ventral polarity; homeodomain repressor; nodal; p38 MAPK; sea urchin embryo; stem cells; symmetry breaking