Fig. 5. XPak3 is involved in cell cycle regulation. (A) Pigmented embryos were injected into one blastomere of two- or four-cell stage embryos with either XPak3-myr RNA or XPak3-MO; these embryos were allowed to develop to the stages indicated. The arrowhead shows the injected side: (1) 50 pg of Xpak3-myr induce cell cycle inhibition before MBT (100%, n = 75); (2) 25 pg give a similar phenotype after MBT (100%, n = 83). (3) Microinjection of 2.5–5 pmol of XPak3-MO induces neural plate expansion (67%, n = 116); (4–6) immunostained embryos showing increased signal on the injected side (arrowhead) for phosphorylated histone H3 (54%, n = 54), BrdU (58%, n = 48) and PCNA (79%, n = 62). (7 and 8) TUNEL staining of embryos injected with 10 pg of XPak3-myr RNA or 2.5 pmol of XPak3-MO shows no significant effect on apoptosis; rather, apoptotic cell death appears to correlate with increased proliferation. (B) Embryos were injected into one blastomere of two-cell stage embryos with either XPak3-myr RNA alone or XPak3-myr RNA and XPak3-MO together. By stage 10–11, XPak3-myr-injected embryos stopped growing (100%, n = 107), while XPak3-myr/XPak3-MO-co-injected ones continued to develop (79%, n = 95). Embryos were fixed at the stages indicated. (C) Deletion mutants of XPak3 were generated and tested for their influence on cell cycle regulation and neuronal differentiation. The corresponding phenotypes are indicated.