Fig. 1. An mnk-null mutation suppresses the cellularization- and gastrulation-defects associated with the grp mutation. (A,B) Control (w¹¹¹⁸) and mnk-null mutant (mnk) embryos cellularize during interphase 14; a uniform monolayer of nuclei surrounded by a hexagonal network of membrane and associated actin network (insets) can be seen. (C) grp-null mutant embryos fail to cellularize and nuclei are either lost from the surface or fuse to form aggregates, and the actin cytoskeleton is disorganized (inset). (D) By contrast, mnk grp double-mutant embryos cellularize and show a near wild-type hexagonal actin network and uniform cortical nuclear monolayer (inset). However, the nuclei are significantly larger than in wild-type or mnk mutant embryos. (A-D) The actin cytoskeleton (green) was labeled with an anti--Spectrin antibody and nuclei were labeled with TOTO3 (Molecular Probes; red). Insets are enlarged images of -Spectrin staining. (E-L) Still images from transmitted light time-lapse recordings of control (w¹¹¹⁸), mnk- and grp-null single mutant, and mnk grp double-mutant embryos. Control (E,F), mnk-null mutant (G,H) and mnk grp double-mutant (K,L) embryos cellularize and gastrulate. By contrast, grp-null mutant embryos (I,J) do not cellularize or gastrulate. Arrows indicate the cellularization front; arrowheads indicate pole cells migrating towards the anterior during gastrulation. Scale bars: 100 µm in A-L; 10 µm in insets in A-D.