Fig. 4. Relative frequency of duct cell progenitors. Eight-week-old pancreata that received tamoxifen at different stages of development were stained for HPAP and counted (see Materials and Methods). Raw numbers are shown in A. The histogram (B) shows the relative frequency of HPAP+ cells in exocrine (green), islet (blue) or duct (red) tissue. Variations in HPAP labeling efficiency induced by TM at different stages were normalized to the exocrine tissue.