TY - JOUR TI - Early asymmetric cues triggering the dorsal/ventral gene regulatory network of the sea urchin embryo AU - Cavalieri, Vincenzo AU - Spinelli, Giovanni A2 - Krumlauf, Robb VL - 3 PY - 2014 DA - 2014/12/02 SP - e04664 C1 - eLife 2014;3:e04664 DO - 10.7554/eLife.04664 UR - https://doi.org/10.7554/eLife.04664 AB - 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. KW - dorsal/ventral polarity KW - symmetry breaking KW - homeodomain repressor KW - nodal KW - p38 MAPK KW - sea urchin embryo JF - eLife SN - 2050-084X PB - eLife Sciences Publications, Ltd ER -