Postfertilization production of Ybx1 is required for embryonic cell proliferation and epiboly initiation. (A) Bright-field images of embryos injected with cMO or yMO. Some yMO-injected embryos underwent yolk collapse and died, thus reducing the number of embryos with the representative phenotypes from 6 hpf to 10 hpf. (B) yMO-injected WT and Tg(ef1α:GFP-ybx1) embryos. Fluorescent images show the GFP-ybx1 transgene expression driven by zebrafish ef1α promoter. (C) Labelling of pH3-positive cells in MO-injected embryos fixed at 4 hpf, with the quantification displayed by box-and-whisker plots in D. *P<0.05; n=9 regions of interest from three embryos; Student's t-test. (E) Confocal z-projections of DAPI staining. Measurement of the nucleus area is presented as mean±s.d. (n=20 nuclei). (F) Quantification of extracted genomic DNAs from equal numbers of cMO or yMO-injected embryos. Each circle represents the value of a sample containing ten embryos. ns, not significant; *P<0.05, **P<0.01; n=3; Student's t-test. Scale bars: 200 μm in A-C; 10 μm in E.