Fig. 3. Cytochalasin D results in disorganized fibres that fail to form a coherent actin cable. Confocal analysis of phalloidin-stained f-actin (green) and propridium iodide (red) was used to assess the effects of cytochalasin D on the organisation of the actin structures within the pouch endoderm (A-D) compared with an untreated specimen (E), all at equivalent stages. (A) Side view of an embryo that was treated by introducing cytochalasin D-soaked bead into the pharyngeal cavity at stage 14– and incubated for a further 5 hours; already there is evidence of aberrant pouch morphology, where pouches are contorted (1pp) or `relaxed' (2pp and 3pp). (B) High magnification of the dorsal tip of a second pouch shows that actin fibres fail to form a supracellular cable when treated with cytochalasin D; this embryo was treated by introduction of a bead into the pharyngeal cavity and incubated for a further 6 hours. (C,D) Mitotic cells (white arrows) are clearly evident within the pouch endoderm of embryos treated with cytochalasin D, either via a bead (C) or injection (D), as they are seen in the pouch endoderm of untreated embryos (E). CD, cytochalasin D. Anterior is towards the left.