Proliferation studies on dre-oprm1 morphants. Phospho-histone 3 (Ser10) immunostaining (red) was assayed on whole-mounts of control and dre-oprm1 morphants of 24 and 48 hpf. The cell nuclei are counterstained with DAPI (blue) to give a better overview of the embryo. Dorsal views of the flat-mounts are shown, and embryos are oriented anterior toward the left and posterior toward the right. A total of 25 embryos were used for each treatment and for each time point, and the experiment was repeated three times. dre-mor MOR, morpholino designed against dre-oprm1 gene.