Expression of the membrane-anchored C-terminal cytoplasmic domain of polycystin-1 induces branching morphogenesis in IMCD cells. (a) CD16.7-positive (control) and CD16.7.PKD1-positive IMCD cells (PKD1) were subjected to branching morphogenesis assays. All cells were positive for the transgene, and expressed the CD16.7 fusion protein at the plasma membrane, as demonstrated by immunofluorescence microscopy of unfixed, nonpermeabilized cells. Expression of the cytoplasmic tail of polycystin-1 induces branching and augments the HGF-stimulated response. (b) IMCD cells cultured for 48 hours in Matrigel in the absence of HGF display a branching, elongated phenotype, as compared to the cystic phenotype seen in control cells. (c) Evaluation of three independent experiments demonstrates the highly significant effect of polycystin-1 on both basal and HGF-stimulated branching morphogenesis. Black bars, basal condition; gray bars, HGF-stimulated IMCD cells. **P < 0.01.