Capping protein activity mediates the function of Wts in polarizing F-actin and promoting border cell migration. (A) Control egg chamber at stage 9. (B) Control egg chamber at stage 10. (C and D) Capping protein β (cpb^M143) mutant border cell clusters are strongly delayed at stage 9 (C) and 10 (D), with strong accumulation of F-actin throughout the border cell cluster (inset), similar to a wts^X1 mutant (see Fig 3). (E and F) wts^X1 mutant clusters rescued by expression of UAS.cpb at stage 9 (E) or 10 (F) migrate normally and show normal F-actin polarization and levels (insets). (G) Quantification of migration index in stage 10 wts^X1 (n = 17) and cpb^M143 mutants (n = 31) and of the rescue of wts^X1 mutants by overexpression of cpb^M143 (n = 41). Bars, 50 µm (5 µm for insets).