Fig. 7.

PI3-kinase regulates formation of elongated, multicellular epithelial tubules. MDCK cells were incubated for 24h with collagen gel overlays lacking (a–c; Control) or containing 20 μM LY-294002 (d–f; Coll/LY-294002). Methanol-fixed cells were double-labeled for gp135 (red staining) and ZO-1 (green staining) to visualize apical membranes and tight junctions, respectively, and examined by confocal microscopy. Incubation with collagen gel overlays induced the formation of elongated, multicellular epithelial tubules with gp135-positive apical lumens and associated ZO-1 positive tight junctions (a–c;arrows). The basal membranes of cells comprising this tubule are outlined (c;dashed line). Incubation with collagen gel overlays containing LY-294002 only allowed the formation of small gp135-positive apical lumens with associated ring-like tight junctions (d–f; arrows). The membranes of the cell pair contributing to this tubule are outlined (f; dashed line). Scale bar, 10 μm.