Par-1 kinase activity is required for Drosophila embryo metaphase compartments. (A) Schematic side views of three cortical nuclei. At interphase and prophase, each nucleus induces an apical actin cap (green) encircled by an actomyosin border (orange; shown in cross section). By metaphase, each cap grows into a compartment for a mitotic spindle. (B) Cycle 12 metaphase. For control RNAi embryos (shRNA targeting nonexpressed mCherry), phalloidin-stained (F-actin positive) furrows fully surround each tubulin-stained mitotic spindle. With par-1 RNAi, many furrows are lost, and abnormal interspindle contacts arise (arrowheads). Coexpression of RNAi-resistant GFP–Par-1 rescues the par-1 RNAi defects, but a kinase-deficient (KD) version does not. Both Par-1 constructs localize to the embryo cortex (bottom right panels). (C) Furrow defects quantified as three classes (see Materials and methods). Embryo numbers on the bars.