Figure 5

New β cells can derive from non-β cells in PDL pancreas. (a) Description of the transgenic mouse and the strategy for labeling and tracing pre-existing β cells (legend as in Figure 4). Tamoxifen s.c. injection (*TAM, 4 mg/injection) of bigenic RIPCre^ERT;R26^lacZ mice of 8 weeks results in transient nuclear translocation of CreERT, leading to removal of the loxP-flanked STOP sequence and permanent heritable expression of the lacZ reporter gene (encoding β galactosidase, bGal) in β cells. A 14 days TAM-washout (WO) period assured the absence of residual TAM at the time of surgery. PDL-surgery was followed by a label-chase period of 14 or 35 days after which islets in PDL head or PDL tail were examined by immunostaining for bGal expression in insulin⁺ cells. Non β cell-derived β cells would dilute the label and decrease the preponderance of bGal⁺ insulin⁺ cells. (b) bGal expression in insulin⁺ cells following 14 or (c) 35-days chase period. Left panels, preponderance of bGal⁺ insulin⁺ cells; right panels, preponderance of bGal⁺ insulin⁺ cells in clusters of different sizes. Data are expressed as the mean±S.E.M. obtained with three mice (*P<0.05, **P<0.01). (d) Immunofluorescent staining for detection of pre-existing (bGal⁺ insulin⁺) β cells in PDL tail and (e) in PDL head, after 35 days chase period. (See also Supplementary Figures S4C,S6 and S7). Scale bars represent 50 μm