Loss of Ddx18 results in G1 cell-cycle arrest and elevated p21 levels. (A-D) DNA histograms from whole embryo cell suspensions (A-B) and Tg(pu.1:EGFP)–expressing cells (C-D) stained with propidium iodide. ddx18^{hi1727/hi1727} mutants (B,D) show increased numbers of cells in G1 and fewer cells in S and G2 phase compared with sibling controls (A,C). (E) Bar chart showing the number of cells in each phase of the cell-cycle in pu.1:EGFP⁺ cells from 3 experiments. *P < .05 (Student t test). (F) qRT-PCR for p21 shows expression of p21 is up-regulated in sorted Tg(pu.1:EGFP)–expressing myeloid cells from ddx18^{hi1727/hi1727} compared with sibling controls. Results of 3 experiments normalized to β-actin. *P < .05 (Student t test).