mTOR-signalling is diminished in developing SLY1-/- and SLY1Δ/Δ DN thymocytes. Cell size, activation of S6 kinase and expression levels of the nutrient receptors CD71 and CD98 were determined as surrogate markers for mTOR activity in thymocytes. Phosphorylation of ribosomal protein S6 was used as a marker of S6 Kinase activity . A. SLY1+/+ DN thymocytes were analysed ex vivo and after 12 h culture on OP9 DL-1 cells. Thymocytes were further subdivided by gating on preTCR-negative and -positive cells. B. Activation of mTOR in preTCR-expressing SLY1+/+, SLY1-/- and SLY1Δ/Δ thymocytes was analysed ex vivo and after OP9 DL-1 culture in vitro for 12 hours. 20 nM Rapamycin was added as a control during the cultivation period to inhibit mTOR activation. Histograms show representative data of four independent experiments (n = 4).