(A) The range of zebrafish phenotypes observed after overexpression of oyster Activin type II receptor (Cg-ActRII). Examples showing the dorsalized phenotypes obtained after overexpression of Cg-ActRII. These phenotypes ranged from the least (D1) to the most severe (D3). Examples showing the ventralized phenotypes obtained after overexpression of truncated DN-Cg-ActRII (dominant negative) lacking the intracellular domain. These phenotypes ranged from the least (V1) to the most severe (V3). (B) Dose-dependent phenotype distribution obtained by overexpression of Cg-ActRII and truncated Cg-ActRII (DN-Cg-ActRII). Results are expressed as percent of embryos showing a given phenotype. The number of embryos injected for each concentration of mRNA is indicated in brackets. Paired comparisons of phenotype distributions obtained for each dose of Cg-ActRII mRNA (a, b, c) or DN-Cg-ActRII mRNA (d, e, f) were statistically tracked using χ² test: Significant differences were observed for a, b, c (P < 10^- 4), d (P < 0.005), e (P < 10^- 4) and f (P < 10^- 3). (C) Characteristic phenotype of somite development alteration (C1) resulting from overexpression of Cg-ActRII compared to wild type phenotype (C2) and of fused eyes phenotypes obtained after overexpression of truncated Cg-ActRII (DN-Cg-ActRII) (25 ng/μL) (C3-4). (D) Whole mount in situ hybridization of zebrafish embryos using the dorsal mesoderm marker Goosecoid (Gsc) (D1-3-5) and the ventro-lateral mesoderm marker Tbx6 (D2-4-6). Expression pattern of gsc and tbx6 genes upon injection of Cg-ActRII and DN-Cg-ActRII (75 ng/μL) at 80% epiboly.