Figure 2

β cells of PDL pancreas redivide without extended delay (‘refractory period‘). Insulin⁺ β cells were scored for CldU and/or IdU labeling using analog-specific antibodies. By labeling a first cell division with CldU (blue) and a second one with IdU (green), sequential divisions result in colabeled β cells (blue and green). (a) Neonatal Balb-c mice received i.p. CldU on day 5 (P5), and i.p. IdU on postnatal day 6 (P6), and were sacrificed 24 h later. P6 mice pancreas displayed high percentages of CldU-single positive (blue nuclei) and IdU-single positive (green nuclei) β cells (red) but only very few double-labeled CldU⁺IdU⁺ β cells (blue and green nuclei). (n=6, 7316 insulin⁺ cells evaluated). Eight-week-old male Balb-c mice underwent PDL surgery and CldU and IdU were sequentially administered via the drinking water: (b) 3 days CldU+3 days IdU (n=6, 8172 β cells counted), (c) 7 days CldU+7 days IdU (n=5, 5505 β cells counted), (d) 7 days CldU+28 days IdU (n=3, 5816 β cells counted). (e) On the basis of the data obtained in (a–d), the likelihood of redivision of β cells was calculated (see formula) and plotted versus duration of the cognate IdU labeling period, fitting the modeled exponential function f(x)=(1-a^x-r)/(1-a^x), where x=days of IdU labeling, a=probability of non-labeling per day and r=refractory period in days. The curve fitted the experimental PDL data (b–d), as well as data obtained by³ for partial pancreatectomy (PPx), pregnant mice (Preg), neonatal mice (Neo), or non-treated mice (non-treated). For comparison, our data on neonatal mice (a) are also represented by a datapoint (*) in (e). See also Supplementary Figures S2 and S3. Scale bars represent 50 μm