Materials. The following antibodies were purchased: anti-Src kinase, anti-Vav2, anti-phosphorylated (pTyr¹⁷²) Vav2, and anti-RhoA (Santa Cruz Biotechnology); anti-phosphorylated (pTyr⁴¹⁶) Src kinase (Cell Signaling Technology, Beverly, MA); and anti-p75^NTR from Promega. Clostridium botulinum C3 exoenzyme, Y-27632, PP1, and PP3 were purchased from Calbiochem. Collagen (type I), fibronectin, and laminin were purchased from Sigma. BDNF, NT3, TrkB-Fc, and TrkC-Fc were gifts from Regeneron Pharmaceuticals (Tarrytown, NY). GST-tagged mDia1-Rho-binding domain and RhoAG17A proteins were purified from Escherichia coli BL21 (DE3) pLysS, as described (1).

Plasmids. The following plasmids were purchased: pUSE-c-Src (Upstate, Charlottesville, VA); and pEGFP-C1 (BD Biosciences, Clontech). The plasmid encoding wild type Vav2 was generously provided by C. L. Carpenter (Harvard University, Boston) (2). The fragment of Vav2D Cat lacking amino acids 202–375 (catalytic Dbl-homology domain) was inserted into the mammalian expression vector p3XFLAG-CMV (Sigma). The coding region of p75^NTR was amplified from a mouse brain cDNA library and ligated into pCMV. The RhoA carrying a G17A mutation was subcloned into the E. coli GST-tagged expression vector pET42a (Novagen). The pCMV-RhoA and pET42a-mDia1-Rho-binding domain plasmids were constructed as described (1).

Small-Interfering RNA (siRNA) Preparation. The siRNA duplexes were synthesized by Dharmacon (Lafayette, CO). The following siRNA target sequences were used: rat p75^NTR, 5'-AAGGAGACATGTTCCACAGGC-3'; rat Vav2, 5'-AAGGTCATCTCTGCCGTGTCC-3'. Control GFP siRNA (Dharmacon) was used as a negative control.

1. Yamauchi, J., Chan, J. R. & Shooter, E. M. (2003) Proc. Natl. Acad. Sci. USA 100, 14421–14426.

2. Marignani, P. A. & Carpenter, C. L. (2001) J. Cell Biol. 154, 177–186.