Misregulation of Gwl by Polo interferes with cell cycle progression. (A) Overexpression of Polo in syncytial embryos compromised for gwl is lethal. Expression of UASp-Polo-Myc was driven by Maternal α-Tub Gal4-VP16 (OE: overexpression). No Tg: no Polo transgene. Error bars: SEM. (B) Western blot analysis of embryos analyzed in A. (C) Phenotypes of embryos where a majority of nuclei are in metaphase. Defects in mitotic entry are observed in embryos from mothers heterozygous for gwl^6a where Polo is overexpressed. Defective nuclei (yellow arrowheads) are characterized by the absence of a spindle, bright lamin staining, and undercondensed chromosomes (quantification is at the bottom).