RAP-011 antagonizes the function of Lft1. (A) Illustrated cross-section of ICM region. Secreted factors from somites, neurotube, notochord, mesenchyme, and endothelial cells can affect erythroid development. (B, left) In situ hybridization for GDF6a, GDF11, Lft1, and BMP4 at 18 hpf. (B, right) Illustration of the expression pattern of various TGF-β family members. (C) Transcript quantification of TGF-β family members in rpl11 morphants compared with control embryos at 48 hpf. (D) hsp:Cre-dsRed transgenic embryos injected with plasmid for the temporal expression of Lft1. Embryos were also treated with IgG or RAP-011. o-Dianisidine staining of embryos at 48 hpf. The arrows point to elevated erythroid cells seen in the caudal vein and head region (D’). Observed phenotype (D): Uninjected (no heatshock) = 30/30, Uninjected (heatshock) = 26/26, Injected (no heatshock) = 26/28, Injected (heatshock) = 25/30, Injected (heatshock) + IgG = 23/25, Injected (heatshock) + RAP-011 = 23/30.