Polarity determinants and F-actin regulators affect F-actin dynamics during early embryogenesis. Columns show successive images from time-series analyses, from pronuclear formation to first mitotic division. Labels for each row of micrographs indicate hallmark events in WT at corresponding timepoints. Wild-type: F-actin becomes enriched in the anterior half of the embryo during the first cell division; maximum enrichment occurs after pronuclear meeting. Note the change from F-actin meshwork to discrete foci. par-6(RNAi) (n = 8): Initial clearing of the posterior end is lost by the time of pronuclear centration and rotation. The cell undergoes an equal cell division. par-2(RNAi) (n = 5): An initial displacement of F-actin occurs as in WT, but after pronuclear meeting F-actin begins to accumulate at the posterior. par-1(RNAi) (n = 11): F-actin becomes hyper-asymmetrically enriched, occupying approximately one-quarter the length of the embryo. No F-actin accumulates at the posterior. cdc-42(RNAi) (n = 6): F-actin progressively becomes asymmetrically distributed until pronuclear meeting, at which time F-actin begins to accumulate at the posterior. F-actin forms a weak filamentous network at the cortex and few foci are observed. pfn-1(RNAi) (n = 6): Only discrete foci are observed at the cortical surface of the embryo. These foci appear to move passively toward the anterior until pronuclear meeting, at which point foci begin to agglomerate into larger foci that disperse throughout the entire embryo cortex. Cytokinesis does not occur. nmy-2(RNAi) (n = 4): Weak depletion of NMY-2 disrupts the actomyosin network at the cortex. Very weak filamentous structures are observed with few thick foci forming at pronuclear meeting. The contractile ring is slow to form and eventually disintegrates (data not shown). arx-1(RNAi) (n = 4): Almost no detectable F-actin structures are observed at the cortical surface. F-actin was recruited to the contractile ring and cytokinesis occurred as in WT. The last two rows depict actin morphology at the cortex (in green) during pronuclear meeting and pronuclear centration and rotation (pronuclei in gray). Scale bar is 10 μm.