FIG. 4.

Trio is required for netrin-1-induced axon outgrowth. (A) Neurite outgrowth of Trio^+/+ or Trio^−/− cortical neurons expressing GFP at day in vitro 1.5 treated with control buffer, netrin-1, or glutamate for 24 h. Scale bar, 25 μm. (B) Quantification of average axon length of cortical neurons presented in panel A. Values are represented as a percentage of average axon length of wt cortical neurons at day in vitro (DIV) 1.5 incubated with control buffer. When indicated, neurons were incubated with control Igs or DCC blocking antibodies before netrin-1 addition. **, P <0.001 for the comparison to wt neurons expressing GFP, except for the dotted line that refers to GFP-transfected Trio-null neurons (n = 8 for +/+ and n = 10 for −/− embryos). (C) Distribution of axon length from panel B. (D) E11.5 dorsal spinal cord explants from Trio^+/+ or Trio^−/− embryos were incubated with control buffer or netrin-1 for 35 h. Scale bar, 100 μm. (E) Quantification of the average length of axon bundles per explant after a 35-h incubation with netrin-1 (n = 10 for Trio^+/+, and n = 4 for Trio^−/− embryos; **, P < 0.001) or after 70 h in the absence of netrin-1 (n = 3 for +/+ and −/− embryos).