Fig. 3. The apical cap is asymmetric and dynamic. (A-F) Three-dimensional imaging and reconstruction of the anterior region of stage 8 egg chambers, showing GFP-Vkg (green), Fas2 (red) and Hoeschst (blue, in A). (A) The original stack is a projection of 20 z sections (total depth is 7.6 µm). (B) Intermediate processing showing BM (green), polar cells (white) and apical cap (blue). (C) The resulting 3D-reconstructed polar cells with the apical cap. (D-F) Three other examples of reconstructed polar cells with their apical cap. Insets in C-F show the apical side of polar cells. The red line is the boundary between the two polar cells. (G-O) GFP-Vkg (green; G-0) egg chambers showing Fas2 (G-L), Crumbs (M,O) or Fas3 (N) in red. The process of apical capping is transient and can be described in four discrete phases (1-4; see text for details). After shedding (L), the BC delaminate and invade the nurse cell compartment (M). During migration (phase 5), a BM containing GFP-Vkg is present in polar cells specifically (M-O), opposite to the apical side (marked with Crumbs in M and O). The polar cell BM is maintained when BCs reach the oocyte (O). Anterior is to the left. Scale bars: in A, 5 µM for A-F; in G, 5 µm for G-O.