Accelerated transition from the double-positive to single-positive thymocytes in Gαi2-deficient mice

Deletion of ai2 subunit of heterotrimeric G proteins induces a 2‐4-fold increase in the proportions of CD4 and CD8 single-positive (SP) thymocytes as compared with wild-type littermates, but how Gai2 is involved in thymocyte development is unknown. To determine a role for Gai2 in a specific developmental stage of thymocyte differentiation, we studied the ontogeny of thymocytes in Gai2deficient mice. Our data show that an accelerated transition from the double-positive (DP) to SP thymocytes, rather than impairment in thymic emigration, accounts for a high proportion of the SP thymocytes in the absence of Gai2. Lack of Gai2 greatly augmented a response of thymocytes to TCRmediated stimulation, as evidenced by enhanced proliferation of the DP thymocytes upon ligation of the TCRs. The augmented response may be the reason behind the expedited transition from the DP to SP thymocytes in the animal. In accordance with this, effects of Gai2 deficiency on CD8 or CD4 SP thymocyte differentiation required engagement of the TCRs with either MHC class I or MHC class II molecule. The abnormal thymocyte development resulted in an increase in positive selection, altered usage of TCR Vb gene, aberrant development of CD41CD251 T regulatory cells and untimely thymic involution, the contribution of which to colitis development in the animal is discussed. These findings reveal a previously unappreciated role for Gai2 protein in clonal selection and functionality of thymocytes.