Macrophage development is dependent on microRNA expression. (A) MZdicer KO embryos were rescued in development by injection of mature miR-430 RNA.²⁶  Comparison of L-plastin⁺ macrophages between WT and rescued MZdicer KO (MZdicer⁺⁴³⁰) zebrafish embryos 24-30 hpf. Macrophage development can be detected in early stages in the yolk sac and after that in the mesenchyme of the head and the blood circulation. Each embryo is shown as an overview (scale bar indicates 1 mm) and as a lateral magnified view of the head (scale bar indicates 100 μm). Nine embryos were analyzed in each experiment. (B) Quantification of L-plastin⁺ macrophage numbers in z-stack image files of whole-mount in situ hybridizations from controls or MZdicer⁺⁴³⁰ zebrafish as shown in panel A. **P < .001 by Student t test. Error bars indicate SD.