Fig. 2. Effect of P18 and P15 on cell growth and aggregation of the atrial epithelium in culture, 4 days after inoculation. (A) Control. Cells were allowed to grow in the serum-supplemented medium. Scale bar, 50 µm. (B) Experiment. The proteins (about 36 µg/ml) were added to the serum-supplemented medium. Note that cells aggregate. Scale bar, 50 µm. (C) In situ hybridization showing in vivo expression of -integrin homolog (blue) in the atrial epithelium (arrow). Scale bar, 20 µm. (D) In vitro induction of -integrin homolog by P18 and P15 (brown). Cell aggregates in culture were suspended by pipetting, mounted on cover slips coated with poly-L-lysine, and immunostained (arrow). Scale bar, 10 µm.