Fig. 3

The newly generated growth of distant metastasis is not dependent on malignant MDCs. A Scheme of the Cre-inducible diphtheria toxin receptor (DTR) transgenic mice (iDTR) system. Crossing the iDTR strain with the MMTV–PyMT-Green/ Sftpc-tdTomato (MPG-ST) strain renders Cre-induced GFP-positive cells sensitive to DT. B Four-week-old MPG-ST and MPG-ST-iDTR mice (n = 6) were injected with 100 ng DT once daily for 3 consecutive days (3-1), 3 times a day for 3 consecutive days (3-3), or 3 times a day for 7 consecutive days (7-3). Mammary glands were analyzed 36 h later. The percentage of GFP-positive cells (a) or apoptotic cells stained with Annexin V (b) in different conditions are indicated. Mice without treatment by DT were used as control (C). Data are Mean ± s.d., n = 3 independent experiments per condition. N.S, no significance; *P < 0.05, **P < 0.01 by Student’s t test. MPG-ST-iDTR mice at 12 weeks (C) or 16 weeks (D) were injected with 100 ng diphtheria toxin (DT) every 8 h for 7 consecutive days. Lung metastases were detected by H&E staining (a–c; Scale bar, 200 μm). Representative images of lung sections without DT treatment (a) and at 1 week (b) or 2 weeks (c) after DT injection. E At 16 weeks, MPG-ST-iDTR mice were injected with 100 ng DT every 8 h for 7 consecutive days. a Reconstructed confocal images of the lung sections were taken at 1 week (left panel) or 2 weeks (right panel) after DT injection. Blue, DAPI; Red, AT2 cells; Scale bar, 50 μm. b The proportion of AT2 cells in lung metastases of MPG-ST-iDTR mice before (non-DT) or after DT treatment. All experiments were performed at least 3 times. Data are expressed as mean ± standard deviation. Abbreviations: MPG, MMTV–PyMT-Green; MGP-ST, MPG/Sftpc-Tomato; MPG-ST-iDTR, MGP/ST/Cre-inducible diphtheria toxin receptor