Plays a central role in late thymocyte development by controlling both positive and negative T-cell selection. Required to sustain and/or integrate signals required for proper lineage commitment and maturation of T-cells. Regulates T-cell development through T-cell antigen receptor (TCR) signaling and in particular through the regulation of calcium influx and phosphorylation of Erk. Interacts with PLCG1, ITK and GRB2. Belongs to the themis family. 3 isoforms of the human protein are produced by alternative splicing. Note: This description may include information from UniProtKB.