Figure 2

actin(RNAi) affects extrusion of polar bodies, chromosome segregation, and relative timing and rotation of mitotic spindles. (A) In wild type, both polar bodies are extruded at the anterior end of the embryo (arrow indicates second polar body). Anaphase during the second round of mitosis occurs asynchronously, with the larger AB cell dividing first. The spindle in the P1 cell rotates and divides later and perpendicularly to the spindle in AB. (B) Class I (n = 5) embryos depleted of actin show synchronous second anaphase spindles. This is a unique case in which the polar bodies appear at the posterior pole of the embryo, indicating a reversal of polarity or that they have migrated with the secretion of the eggshell. (C) Class II (n = 5) embryos show anaphase spindles in the second division that are both synchronous and oriented parallel to each other. (D) Class III (n = 4) embryos show chromosome segregation and spindle elongation defects at anaphase in the first and second divisions. (E) Class IV (n = 4) embryos fail to extrude both polar bodies, which remain attached to the maternal pronucleus. Chromosome segregation and spindle elongation defects can also be seen (insets in D and E). Arrows in A-E point to polar bodies. Arrowheads in insets (D and E) point to chromatin bridges. Scale bar is 10 μm.