Notch signaling defect in the thymi of Mib1 conditional KO mice. (A) The lethally irradiated MMTV-Cre;Mib1+/f (black) and MMTV-Cre;Mib1f/f (red) mice (7–9 wk old) were injected i.v. with BM cells from the TNR mice (51). At 4 wk after transplantation, the thymocytes were analyzed by flow cytometry for GFP expression gated on the CD4−CD8− DN thymocytes. Percentages indicated are mean ± SD from three independent experiments. (B–D) The lethally irradiated MMTV-Cre;Mib1+/f and MMTV-Cre;Mib1f/f mice were transplanted with CD45.1 BM cells. 6 wk after transplantation, the thymi were fixed and cryosections were immunostained with anti-Dll1 (B and C, red), anti-Hrs (B, green), anti-cytokeratin (C and D, green), and anti-Mib1 (D, red) antibodies with HOECHST (blue). Note that Dll1 was colocalized with Hrs (B, arrowheads) in the MMTV-Cre;Mib1+/f thymus, whereas it accumulated in the cytokeratin-positive cortical epithelial cells of the MMTV-Cre;Mib1f/f thymus (B and C, asterisks). The arrowheads in C and D show the expression of Dll1 and Mib1, respectively. A representative of three independent experiments is shown. Bars, 5 μm.
