Ogt overexpressing embryos have defects in the yolk cytoskeleton. Confocal z-stacks of immunofluorescent images of embryos injected with β-galactosidase mRNA (A, D, G, J), variant 4 ogt mRNA (B, E, H, K) and hOga mRNA (C, F, I, L). Embryos at 4 hpf were incubated with the 12G10 1° antibody to reveal microtubule filaments (A-F) and 8 hpf embryos were incubated with rhodamine phalloidin (G-L). 12G10 reactivity reveals mitotic spindles in the blastomeres of controls embryos (A) Ogt expressing embryos (B) and hOga embryos (C). Within the yolk, long MT arrays extend around through the cortical cytoplasm toward the vegetal pole (A, D, arrowhead). In Ogt expressing embryos, many MTs appear thicker than normal and the arrays do not extend far towards the vegetal pole (B, E, arrowhead). Similarly, the MTs in the yolk are thicker than normal in hOga expressing embryos (F, arrowhead). Staining with rhodamine-phalloidin reveals actin filaments associated with the plasma membranes of EVL cells and the contractile actin ring in the yolk syncytial layer (YSL) (G-L). The contractile actin ring is apparent within the YSL of controls (G, J arrow), but not in OGT overexpressing embryos (H, K, arrow) or hOga expressing embryos (I, L, arrow). The EVL cells are highly irregular in size and shape in Ogt overexpressing embryos (H, K) and hOga expressing embryos (I, L). Red lines indicate the position of the YSL (A-C). Animal pole is to the top. Bars = 100 μm.