Inhibition of Rho at different stages of thymocyte development gives different perspectives on Rho function

• Published in: Current biology Vol. 9; no. 12; pp. 657,S1 - 660,S1
• Main Authors: Cleverley, Steve, Henning, Stefan, Cantrell, Doreen
• Format: Journal Article
• Language: English
• Published: England Elsevier Inc 17.06.1999
• Subjects: ADP Ribose Transferases - genetics; ADP Ribose Transferases - metabolism; Animals; Botulinum Toxins; CD2 Antigens - genetics; CD2 Antigens - metabolism; Cell Differentiation; Clostridium botulinum - enzymology; Clostridium botulinum - genetics; Female; Genes, Bacterial; GTP-Binding Proteins - metabolism; GTPase-Activating Proteins; Lymphocyte Specific Protein Tyrosine Kinase p56(lck) - genetics; Lymphocyte Specific Protein Tyrosine Kinase p56(lck) - metabolism; Male; Mice; Mice, Transgenic; Receptors, Antigen, T-Cell, alpha-beta - genetics; T-Lymphocytes - cytology; T-Lymphocytes - immunology; T-Lymphocytes - metabolism
• ISSN: 0960-9822; 1879-0445
• DOI: 10.1016/S0960-9822(99)80289-9

Development of thymocytes can be staged according to the levels of expression of the cell-surface markers CD4, CD8, CD44, CD25 and CD2. Thymocyte development is regulated by a complex signalling network [1], one component of which is the GTPase Rho. The bacterial enzyme C3 transferase from Clostridium botulinum selectively ADP-ribosylates Rho in its effector-binding domain and thereby abolishes its biological function [2,3]. To explore the function of Rho in thymocyte development, we previously used the proximal promoter of the gene encoding the Src-family kinase p56lck to make transgenic mice that selectively express C3 transferase in the thymus [4–6]. In these mice, which lack Rho function from the earliest thymocyte stages, thymocyte numbers are reduced by approximately 50- to 100-fold. Here, we describe transgenic mice that express C3 transferase under the control of the locus control region (LCR) of the CD2 gene; this regulatory element drives expression at a later stage of thymocyte development than the lck proximal promoter [7]. In these mice, thymocyte numbers were also reduced by 50- to 100-fold, but unlike the lck–C3 mice, in which the reduction predominantly results from defects in cell survival of CD25+ thymocyte progenitors, the CD2–C3 transgenic mice had a pre-T-cell differentiation block at the CD25+ stage after rearrangement of the T-cell receptor (TCR) β chains. Analysis of CD2–C3 mice demonstrated that Rho acts as an intracellular switch for TCR β selection, the critical thymic-differentiation checkpoint. These results show that Rho-mediated survival signals for CD25+ pre-T cells are generated by the extracellular signals that act on earlier thymocyte precursors and also that temporal cell-type-specific elimination of Rho can reveal different functions of this GTPase in vivo.