Fig. 5. Activation of the MAP kinase pathway is compromised in Frs2^cn prostates during branching morphogenesis. (A,B) Western analyses (A) of the indicated proteins from Triton-extracts of mouse prostates at the indicated ages. β-actin was used as a loading control. Note that phosphorylated FRS2 and ERK1/2 were prominent in 1- and 2-week-old prostates and were diminished in 4-week-old prostates, whereas phosphorylated AKT remained constant in the prostates. The specific bands were quantitated (B) by densitometry. (C,D) Immunostaining of phosphorylated ERK1/2 (C) and phosphorylated AKT (D) in tissue sections of 1-week-old prostates. The specific staining was visualized with confocal microscopy. Note that phosphorylated ERK1/2 was reduced in the epithelial cells, but not in the stromal cells, of Frs2^cn prostates, and that both phosphorylated ERK1/2 and phosphorylated AKT were reduced in epithelial cells of Fgfr2^cn prostates. Arrows indicate epithelial cells. (E) Newborn prostate rudiments cultured with 10 µM ERK1/2 (MEK1/2) or PI3 kinase inhibitor, as indicated, for 3 days. Arrows indicate lumens of the prostatic ductal structures. pERK1/2, phosphorylated ERK1/2; pAKT, phosphorylated AKT; F/F, homozygous Frs2^flox mice; CN, Frs2^cn mice.