Cdk1 is enriched at cell junctions. (A) Left: Image from a live stage 10 embryo expressing eGFP-Cdk1. Image shown is z-projection of apical region showing the native GFP signal along junctions, particularly tricell junctions. Bar, 20 µm. Right: Stage 10 embryo fixed and immunostained with antibody specific for Y15 phosphorylated Cdk1 (pCdk1). Bar, 20 µm. Arrows show tricell junctions. (B) Left: Stage 10 control embryos immunostained with ZO-1 (red) and Cdk1–phosphorylated tyrosine 15 (green). Bar, 10 µm. Right: A 3D projection of the boxed region, rotated 90 degrees, with the apical surface to the right. Bar, 2.5 µm. (C) Apical projections of stage 10 embryo fixed in methanol/DMSO and immunostained with antibodies for cyclin B. Arrows show tricell junctions. Bar, 20 µm. (D) Midcell projections of stage 10 embryo fixed in formaldehyde and immunostained with antibodies for cyclin B (green) and microtubules (red). Arrowhead shows poleward spindle staining of cyclin B. Bar, 20 µm. (E) Apical projection of stage 10 embryo fixed in methanol/DMSO and immunostained with antibodies for cyclin B (green) and ZO-1 (red). Bar, 20 µm. (F) Series of still images from a movie of stage 10 embryos expressing mChe–histone H2B (red) and cyclin B–GFP (green). Time stamps indicate minutes after first frame. Bar, 20 µm. See also Video 1.