MADD-2 promotes stable UNC-40–mediated F-actin polarization. Anterior is left; ventral is down. (A) Time series shows F-actin stably polarized at the basal surface of the AC of a wild-type animal. (B) The volume of the stable basal F-actin patch (green line). (C) Similar localization in four other cases. (D) The time series shows multiple mislocalized F-actin patches in the AC of a madd-2 mutant. (E) The volume of individual F-actin patches in a madd-2 mutant. Green lines represent basal patches, and purple lines represent mislocalized patches. (F) Similar analysis of four additional madd-2 mutants. Large mislocalized F-actin patches were observed in 50% of madd-2 mutants (n = 6/12) but were not observed in any wild-type animals (n = 10/10). Isosurface thresholds were set to a stringent level that delineated ectopic and basal patches in madd-2 animals to evaluate the AC’s ability to polarize F-actin at the invasive membrane toward endogenous UNC-6 (see Materials and methods). This thresholding resulted in a reduction of reported F-actin volume compared with previous figures. All animals were examined at the P6.p two-cell stage. Bars, 5 µm.