Figure 5: Blocking E and F divisions halts BM gap movement in an integrin-dependent fashion.

(a–j) DIC micrographs (left) and corresponding confocal sections of the BM (laminin::GFP, right). Dorsal schematics (far left) indicate the position of the VPCs at each developmental stage with the dashed black line denoting the location of the single lateral confocal slice depicted by the corresponding micrographs (right). Black arrowheads indicate position of the AC, white arrows delineate the BM gap, dashed lines, yellow and red asterisks indicate the D, E and F cells, respectively. (a–j) Pie charts depict BM gap position at the P6.p four- through eight-cell stages, n=40, 22, 56, 52, 41, 28, 14, 42, 46 and 32 cases observed for each stage, respectively (see Supplementary Fig. 5 for BM gap measurements and Supplementary Tables 2b,c for scoring data). (a–e) Expression of cdh-3>CKI-1::GFP (right) blocked the terminal division of the E and F cells (c,d) and inhibited BM gap expansion beyond these cells. (f–j) Expression of a dominant negative PAT-3 β-integrin construct (HA-β-tail) in the C-F cells (egl-17>HA-β-tail, expressed most strongly in the vulE and vulF precursors) resulted in a progressive overexpansion of the BM gap boundary when E and F cell division was blocked by expression of cdh-3>CKI-1::GFP (yellow arrows). (j) By the mid-L4 stage, the BM gap boundary expanded beyond the E and F cells 66% of the time (*P<0.0002; n=32, Fisher’s exact test as compared with (e, n=41)). Scale bar, 5 μm.