Gads-/- mice reveal functionally distinct subsets of TCRβ+ CD4-CD8- double-negative thymocytes

TCR beta expression in CD4(-)CD8(-) double-negative (DN) thymocytes induces signaling pathways that promote survival and proliferation, as well as differentiation into CD4(+)CD8(+) double-positive thymocytes. The signaling pathways that regulate survival, proliferation, and differentiation remain unclear. We used Gads-deticient mice to investigate the signaling pathways that regulate these cell fates. During this investigation, we focused on TCR beta(+) DN thymocytes and found that there are at least three functionally distinct subsets of TCR beta(+) DN thymocytes: TCR beta(+) DN3E, TCR beta(+) DN3L, and TC beta 3(+) DN4. Survival and proliferation of TC beta(+) DN3E were independent of Gads, but survival and proliferation of TCRP+ DN3L cells were Gads dependent. Likewise, expression of Bcl-2 in TCR beta(+) DN3E cells was Gads independent, but Gads was necessary for Bcl-2 expression in TCR beta(+) DN3L cells. Bcl-2 expression was not dependent on Gads in TCR beta DN4 cells, but proliferation of TCR beta(+) DN4 cells was Gads dependent. Gads was not required for the differentiation of DN thymocytes into DP thymocytes. In fact, Gads(-/-) DN3E cells differentiated into DP thymocytes more readily than wild-type cells. We conclude that signaling pathways required to initiate TCR beta-induced survival and proliferation are distinct from the pathways that maintain survival and proliferation. Furthermore, signaling pathways that promote survival and proliferation may slow differentiation.