(A–G) Single notochord cells from embryos expressing H2A-RFP (nuclear RFP), and either a Pk-myc or Stbm-Venus fusion protein (as indicated). Arrowheads indicate anteriorly localized reporter protein. Embryos were treated with either DMSO (vehicle), cytochalasin B, latrunculin B, or blebbistatin (also as indicated). (H, I, and J) Cortical actin staining of notochord cells with phalloidin in embryos treated with vehicle only (DMSO), cytochalasin B, or latrunculin B, as indicated. Arrows in H indicate the equatorial contractile ring of actin. (H′, I′, and J′) Co-staining of samples for the cortical protein atypical protein kinase C (aPKC). Arrowhead in H′ indicates concentrated staining at center of cell cortex. Scale bar in A is 5 μm.