Survival and Developmental Progression of Unselected Thymocytes in the Absence of the T Cell Adaptor Gads

Thymic development is tightly regulated by TCR signaling via the immune adaptors SLP-76 and LAT. Gads bridges the TCR-induced recruitment of SLP-76 to LAT; yet is not absolutely required for thymic progression. To better identify Gads-dependent developmental transitions, we performed tamoxifen-induced ablation of Gads (GadsiKO), accompanied by expression of tdTomato, and compared the development of Gads-expressing (Tom-) and - ablated (Tom+) thymocytes within the same mouse. The frequency of GadsiKO (Tom+) thymocytes decreased at {beta}-selection and positive selection, confirming the Gads-dependence of these junctures; nevertheless, we observed small populations of positively-selected GadsiKO SP thymocytes. Consistent with a signaling defect, expression of CD5 was strongly impaired at the {beta}-selection checkpoint and within the DP compartment; moreover, GadsiKO DP thymocytes exhibited reduced TCR-induced calcium flux. Surprisingly, MHC-non-responding (CD5-) GadsiKO DP thymocytes exhibited reduced death by neglect; instead, aberrant populations of CD5- GadsiKO thymocytes progressed as far as the CD4 SP compartment, while lacking key characteristics of positively selected thymocytes. In an experimentally-induced model of death by neglect triggered by CD8 crosslinking, Gads was required for the preferential apoptosis of CD5lo DP thymocytes. Our results suggest that Gads promotes passage through TCR-driven developmental checkpoints while also promoting the death by neglect of unselected thymocytes.