a, Schematic of lineage tracing in TertCreER mice treated with a single dose of tamoxifen on postnatal day 60 and analysis at indicated time points. Mo, month. b–d, Immunohistochemistry for Tomato in Ptf1aCreER mice 10d post tamoxifen (5mg (b), 0.5mg (c) and 0.05mg (d)) injection (n=4 mice). e, Distribution of Tomato-positive acinar cells per clone for each time point in Ptf1aCreER mice (each color represents one mouse; n=4 for each time point) f, TertCreER mice are injected with Tamoxifen (5mg) on postnatal day 60 and put on BrdU water (1mg/ml) for 30 days. g, Immunofluorescence analysis of a TertCreER pancreas after 30 days of BrdU water. Tomato (red), BrdU (green) and DAPI (blue) are shown. TERTHigh Tomato/BrdU double positive cells (green arrow) and TERTLow BrdU positive cells (orange arrow) shown. h, Quantification of TERTLow and TERTHigh BrdU+ cells (n=5 mice) (mean ± SD). i–k, Single-molecule RNA FISH for Tert on FACS-purified bulk (i), TERTHigh (j) and TERTLow derived (k) acinar cells of TertCreER mice(n=3). Scale bars, 25µm (g), 50µm (i–k), 100 µm (b–d). P values calculated by two-sided Mann-Whitney test (h).