Fig. 4. Cytoskeletal actin disruption does not inhibit DNA replication. (A) Untreated 24-hour-old control zygotes showing zygotic polarization and mitotic division. Zygotes were loaded with 1.0 µM DiOC₆(3) for 15 minutes to visualise daughter nuclei (yellow arrows) by negative staining. (B) Representative 24-hour-old zygote (n>100) treated with 0.1 µM latrunculin B continuously from 20 minutes after fertilization and showing complete mitosis, but no zygotic polarization or cytokinesis (no dividing cell wall). The zygote was imaged with two separate confocal scans to allow for the different depths of each daughter nucleus (yellow arrows). (C) Representative 24 hour old zygote (n>100) treated continuously with 1.0 µM latrunculin B. The nucleus is displaced from the usual central location, but the chromosomes are condensed, indicating M-phase entry. (D) Enlarged section from C highlighting condensed chromosomes. (E) Cytoskeletal actin disruption does not inhibit entry into M phase. Zygotes were treated with 0.1 µM latrunculin B continuously from 30 minutes after fertilization (black circles) or not treated (white circles), and scored for entry into M phase by the presence of condensed nuclei (visualized by staining with 5 µM fluorescein diacetate and 100 µM Hoechst 33342). Data are mean±s.e.m. (F) Cytoskeletal actin disruption does inhibit polarization. Length/width ratios were measured for the zygotes in E. Control zygotes (white circles) displayed steady growth which was completely inhibited in 0.1 µM latrunculin B-treated zygotes (black circles). Data are mean± s.e.m.; ^*P<0.05.