Fig. 4. Aub, Osk and Vas in structures characteristic of polar granule material. Donut-shaped structures in pole cells of cellularized embryos contain GFP-Aub (A), Osk (B,E) and Vas-GFP (D). Each of the structures containing GFP-Aub also contains Osk, as shown in the overlap of the two signals (C). Note that GFP-Aub is limited to the cytoplasm (filled arrowheads), with the nuclear Osk-containing donut-shaped structures lacking Aub (open arrowheads). All Osk-containing structures also include Vas-GFP, as seen in the overlap of the Osk and Vas-GFP signals (F). Scale bar: 5 µm. Most of the donut-shaped structures have diameters of approximately 0.5 to 1.0 µm, consistent with a diameter of 0.75 µm to 1.0 µm for polar granules and nuclear bodies as reported by Mahowald (Mahowald et al., 1976).