Figure 2. .

GDF1 activity assay by morphological phenotype. Twenty picograms of mRNA synthesized from humanized wild-type (WT) and mutant GDF1 constructs were injected at the one-cell stage. Embryos were allowed to develop for 27 h and were assayed for severity of developmental defects. Representative samples from injected clutches are shown. WT humanized GDF1 exhibited the severest developmental defects indicative of strongest activity. Mutant GDF1 constructs exhibited varying degrees of decreased activity compared with WT GDF1. Uninjected WT embryos are included for comparison. Twenty picograms of LacZ mRNA was injected as control and did not exhibit any phenotype (data not shown). mGDF1 = murine GDF1.