Fig. 3. (A) Distribution of bifurcations in 5 day DMSO- and DAPT-treated metanephroi. DBA-stained metanephroi were examined as described in the Materials and methods, and the frequency of branches with the given number of bifurcations was determined. Note the shift to fewer bifurcations in DAPT. This is not due to loss of Ret signaling, because even in the presence of DAPT, Ret was activated in response to 40 ng/ml Gdnf, as judged by Ret tyrosine phosphorylation (at the autocatalytic tyrosine Tyr905 and at Tyr1062) and subsequent activation of the downstream MAPK pathway (B).