ST3Gal-IV is dispensable for the proliferation of ETPs in vivo and the in vitro development of thymocytes. Flow cytometric analysis of the proliferation (A) and apoptosis (B) of ST3Gal-IV–deficient and WT ETPs. MBMC mice were generated as described in Figure 1 and injected with EdU 6 hours before euthanasia. Histograms show the frequency of EdU-positive (A) or active caspase 3–positive (B) ST3Gal-IV–deficient (KO) or WT ETPs in the thymus of 1 representative mouse. Bars show the mean ± SEM frequency of EdU-positive (A) or active caspase 3–positive (B) WT (blue) or ST3Gal-IV-deficient (red) ETPs of 2 independent experiments with 8 total mice. (C) Flow cytometric analysis of thymocyte development in the OP9-DL1 coculture system. Sorted WT (CD45.1) and ST3Gal-IV–deficient (CD45.2) LSK cells were cocultured in the same well on OP9-DL1 cell layer. Dot plots show the frequencies of the various thymocyte populations at days 8, 12, 16, and 21 of culture of gated KO or WT cells. The dot plots are representative for 3 independent experiments.