UNC-40 (DCC) presages and then enriches at the basement membrane breach. (A) The netrin receptor UNC-40::GFP (middle, arrow) enriches at the site of basement membrane breach (right, arrow). (B) A ventral view time series shows that UNC-40::GFP (middle row, arrows) presages and then progressively enriches at the basement membrane breach as it expands (bottom, arrows). (C) Timing of basement membrane breach in wild-type, unc-40 (e271), and unc-6 (ev400) mutant animals (n ≥ 14 animals observed for each genotype, at each time point). Timing was assigned in relationship to the divisions of the neighboring uterine and P6.p vulval cells (Fig. S1). The time between the mid P6.p two-cell stage when wild-type animals initiate breach and early P6.p four-cell stage when unc-40 mutants penetrate basement membrane is ∼1.5 h at 20°C. Bars, 5 µm.