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Fig. 3 Overexpressed Bmp2 homodimers require both Bmpr1 and Acvr1 to signal: The HA-bmp2b RNA injected is 5- to 40-fold (5 to 10 pg) above the rescuing concentrations (0.25 to 1 pg) shown in SI Appendix, Fig. S4. Raw phenotype scores are shown in Dataset S2. MO concentrations and combinations are listed in SI Appendix, Table S4. (A) Overexpressed Bmp2 homodimers require Bmpr1 to signal. The bmp2b overexpression ventralizes bmp7−/− embryos (columns 1 and 2). The bmpr1a MO knockdown abates signaling caused by bmp2b overexpression (column 3). Efficacy of the bmpr1a MO mix is affirmed in WT embryos (columns 4 and 5). (B) In one model, the BMP2 homodimer forms a Bmpr1–Bmpr1 complex. (C) Overexpressed Bmp2 homodimers require Acvr1 to signal. Overexpressed bmp2b RNA ventralizes bmp7−/− embryos (columns 1 and 2). The acvr1l MO knockdown abates signaling caused by bmp2b overexpression (column 3). Efficacy of the acvr1l MO is affirmed in WT embryos too (columns 4 and 5). (D) In another model, the BMP2 homodimer binds to Acvr1 and Bmpr1. (E) Bmpr1–Acvr1 heteromeric complex is necessary for BMP2 homodimer signaling in the zebrafish.