DDX18-E76del expression in ddx18^hi1727/+ animals identifies a dominant-negative effect on myeloid cells. (A-F) Expression of control (mCherry encoding; A-B), DDX18-WT encoding (C-D), or DDX18-E76del (E-F) encoding RNA in ddx18^{hi1727/hi1727} mutant (A,C,E) or ddx18^+/+ (B,D,F) embryos shows the DDX18-E76del variant cannot rescue the phenotype of ddx18^{hi1727/hi1727}. Lateral views, head to the left, dorsal upward of 27-hpf embryos. (G) Quantitation of myeloid cell numbers from individual genotyped (imaged) embryos injected with control, DDX18-WT, and DDX18-E76del encoding mRNAs. Embryos injected with control or DDX18-WT encoding RNA show no difference in myeloid cell numbers between heterozygous ddx18^hi1727/+ and ddx18^+/+ siblings. Embryos injected with DDX18-E76del encoding mRNA, however, have a statistically significant reduction in myeloid cell numbers compared with control or DDX18-WT–injected ddx18^hi1727/+ siblings. **P = .002 (unpaired Student t test).