The role of the guanine nucleotide exchange factor Tiam1 has long been known to stimulate the outgrowth of neurons (see here) by shifting the Rac / Rho actin polymerization equilibrium (see here) towards Rac. Now Fard et al. have used RNA interference in cell culture to show that Tiam1 is specifically associated with NGF/TrkA-dependent neurite elongation. Here is the mechanism they propose, involving tyrosine kinase receptors:
RNA interference is a useful technique for evaluating mechanisms. As opposed to pure gene knock-out studies, it can allow for the evaluation of a more dose-dependent relationship.
Shirazi Fard S, Kele J, Vilar M, Paratcha G, Ledda F (2010) Tiam1 as a Signaling Mediator of Nerve Growth Factor-Dependent Neurite Outgrowth. PLoS ONE 5(3): e9647. doi:10.1371/journal.pone.0009647