Increased apoptosis of OP9 cultured DN thymocytes in the absence of functional SLY1 protein. A. Cell cycle analysis of permeabilized DN cells after 2 days of OP9 DL-1 culture using DAPI. B. AnnexinV and DAPI staining of DN thymocytes cultivated for 4 days on OP9 DL-1 cells. C. SLY1-targeting results in increased Caspase-3 activation independent of TCRβ-expression and Notch signalling. Sorted DN3 thymocytes were cultured on OP9 cells for 2 days and then Caspase-3 active fragment in DN cells was analysed dependent on TCRβ-expression. D. Intracellular Caspase-3 activation in DN4 cells is negligible. *p ≤ 0.05; **p ≤ 0.01; *** p ≤ 0.001.