“…Pre-TCR ligation or TCR-MHC interactions result in transcriptional induction of the RasGRP1 gene (Norment et al, 2003;Tiong Ong et al, 2003), and biochemical activation of RasGRP1 is dependent on signal transduction from TCR via phospholipase Cg1 Bivona et al, 2003). Although RasGRP1 is not required for pre-TCR-directed b selection in normal mice (Dower et al, 2000), constitutive transcription of RasGRP1 from a transgene confers partial developmental progression up to the DP stage in the absence of pre-TCR (Norment et al, 2003). The efficiency of TCR-directed positive selection of DP thymocytes is severely compromised in RasGRP1-deficient mice (Dower et al, 2000;Priatel et al, 2002;Layer et al, 2003).…”