Fig. 1. Three domains of yolk-stalk diameters and depth of cellularization. Wild-type embryos stained for Myosin. (A) Cross-section of late-cellularization embryo showing depth of cellularization. (B) Same embryo as in A observed in grazing section at the depth of the furrow canals. (C) Higher magnification view of B. Arrows in B,C indicate anterior domain, arrowheads indicate pre-CF domain. (D-F) 1 µm optical sections of wild-type embryo proceeding from interior of embryo (D) towards surface-most section (F). Each section is separated from the next by 2 µm. Arrows indicate pre-CF domain. (G,H) +/CyO, hb-lacZ embryo stained for Myosin (basal localization, same as in A) and ß-gal (cytoplasmic). These embryos are normal for cellularization, but the cytoplasmic ß-gal allows for easier visualization of cell depth. The great difference in the depth of cellularization between the anterior pole (15-20 µm) and the rest of the embryo (35 µm) means that this difference can be seen in a cross-sectional view of the embryo. The small difference in depth between the pre-CF domain and the posterior domain (a difference of 2-3 µm) means that this difference can not be easily viewed in cross-section (G,H), but can be visualized with optical sectioning technique (D-F).