PI(4,5)P2/AM injection causes shortening of the cells and exclusion of nuclei from the epithelium. (A–A″) Still frame from time-lapse two-photon movies of a cellularizing embryo expressing histone::GFP injected before the beginning of cellularization with: carrier (A), PI(4,5)P2/AM (A′), and PI(3,4,5)P3/AM (A″) taken 50 min after the beginning of cellularization. In control-injected embryos nuclei area attached at the cortex and elongate over the course of cellularization (A). In PI(4,5)P2/AM-injected embryos, nuclei remain trapped in actomyosin hyper-constricted rings and are dragged toward the interior of the embryo (A′). PI(3,4,5)P3/AM-injected nuclei do not elongate and detach from the cortex, resulting in multi-layering (A″). Red line indicates the furrow position in each condition. (B–B″) Still frame from time-lapse two-photon movies of a cellularizing embryo expressing Spider::GFP injected before the beginning of cellularization with: carrier (B), PI(4,5)P2/AM (B′), and PI(3,4,5)P3/AM (B″) taken 50 min after the beginning of cellularization. In control-injected embryos plasma membrane invaginates uniformly, giving rise to cells of ∼40 µm (B). In PI(4,5)P2/AM-injected embryos, plasma membrane invaginates in an irregular manner, resulting in the formation of shortened cells (B′). PI(3,4,5)P3/AM-injected embryos show no delay in the rate of plasma membrane invagination, although cells have an abnormal shape (B″). The red line in B′ and B″ indicates the cell length of the control-injected embryo shown in B. Bar, 10 µm.
