Figure 1. Rho-GTPases and thymic development of T cells. Differentiation of T cells occurs within the thymus. Most T cells develop along 3 steps: CD4^- CD8^- double negative (DN), CD4⁺ CD8⁺ double positive (DP) and mature CD4⁺ or CD8⁺ single positive (SP) stages. Key regulatory signals are mediated through both the pre-TCR and TCR complexes. Signals from the pre-TCR allow cells to differentiate into DP cells and proliferate (β-selection). DP T cells rearrange their TCR and undergo further maturation process that leads to positive selection or nedative selection depenting to TCR binding avidity. DP cells with a MHC class I-restricted TCR differentiate into CD8⁺ SP T cells, whereas MHC class II-restricted cells are directed into CD4⁺ SP T cells. The Rho-GTPases shown to influence thymic selection using Rho-GTPases-deficient mice are indicated in the figure and discussed in more detail in the text.