FIG. 2.

Sonic hedgehog does not recruit quiescent CGNPs into the cell cycle. CGNPs were treated with Shh for 24 h after the indicated period of serum withdrawal, and then DNA synthesis levels were determined by measuring BrdU incorporation (solid bars). Alternatively, serum was replaced with Shh for 3 h; CGNPs were then serum and Shh starved for the indicated periods, after which Shh was added back for 24 h (striped bars). Note that Shh promoted significantly (approximately sixfold) increased levels of proliferation up to 6 h after serum withdrawal but not thereafter (solid bars). Similar results were obtained when an Shh pulse (3 h) was initially applied (striped bars). The infinity symbol (∞) indicates samples in which Shh added at t = 0, removed after 3 h, and measured for BrdU incorporation 24 h later (no Shh retreatment). Shh-induced BrdU incorporation is shown as the fold increase over baseline levels of BrdU incorporation in samples treated with vehicle alone. All data shown reflect results of three independent cerebellar preparations per time point treated with Shh versus vehicle alone. The asterisks indicate significant differences between Shh- and vehicle-treated CGNPs at P < 0.01 (∗∗) and P < 0.05 (∗) confidence levels.