Reduced <i>bmp</i> expression but intact BMP signal transduction in <i>p18ahub</i> mutants.

<p>(A–H) <i>In situ</i> hybridization on early gastrula stage embryos or equivalent, except (C) and (D) are mid gastrula stage or equivalent. Embryos were stage-matched. Animal pole views, dorsal to the right for all. Expression of <i>bmp</i> ligand gene in WT embryos (A, n = 32, C, n = 43, and E, n = 21) and <i>p18ahub</i> embryos (B, n = 30, D, n = 18, and F, n = 16). Expression of the BMP antagonist <i>chordin</i> (<i>chd</i>) was confined to the dorsal side of WT embryos (G, n = 21) but was expanded around the entire margin of <i>p18ahub</i> embryos (H, n = 20) by early gastrulation. (I–N) Pie charts indicate fractions of embryos at 24 hpf that displayed the indicated phenotypes (categories described in the text). Number of embryos is shown at the center of each chart. <i>p18ahub</i> embryos (I, O, uninjected) that were injected with 20 pg <i>bmp2b</i> mRNA were rescued to WT or ventralized (K, P, +<i>bmp2b</i> mRNA) similarly to WT embryos (J, +<i>bmp2b</i> mRNA). <i>p18ahub</i> mutant embryos (L, uninjected) depleted of Chordin, Noggin1, and Follistatin-like 2b proteins by MO injection were similarly ventralized (N, +MO<i>cnf</i>) to WT embryos (M, +MO<i>cnf</i>).