Extended Data Figure 1. Embryo orientation for beads injection and live imaging.

(a) Body axis (red lines) of the Drosophila embryo. A transverse cross section of the embryo at 50% egg length is shown in blue. V: ventral; D: dorsal. (b) The definition of x, y coordinates used in this study. x-axis: ML-axis; y-axis: AB-axis. (c, d) Injection of uncoated fluorescent beads (c) or WGA-coated beads (d) into the cytoplasm or the perivitelline space of an embryo, respectively. The embryo is glued to the coverslip on its dorsal side (method 1). (e) Injection of uncoated fluorescent beads into the cytoplasm of an embryo with its ventral side glued to a coverslip (method 2). Method 1 is better suited than method 2 to introduce beads into the perivitelline space, while method 2 has the advantage of keeping the ventral side free of wound. Note that in method 2 the ventral surface of the embryo is slightly flattened due to contact with the coverslip. This nevertheless does not affect the hydrodynamic characteristics of the cytoplasmic flow. Method 1 was applied in experiments used for Fig. 1 and 2. Method 2 was applied in experiments used for Fig. 3–4 and Extended Data Fig. 10.