100 80 60 40 20 4 6 12 months after tamoxifen injection Figure Q22-2 Percentage of labeled B cells in pancreatic islets of mice at different ages (Problem 22-7). All mice were injected with a pulse of tamoxifen at 6 to 8 weeks of age and then stained for human placental alkaline phosphatase (HPAP) at various times afterward. Error bars represent standard deviations. percent of B cells expressing HPAP
The origin of new β cells of the pancreas—from
stem cells or from preexisting β cells—was not resolved
until a decade ago, when the technique of lineage tracing
was used to decide the issue. Using transgenic mice that
expressed a tamoxifen-activated form of Cre recombinase
under the control of the insulin promoter, which is active
only in β cells, investigators could remove an inhibitory
segment of DNA and thereby allow expression of human
placental alkaline phosphatase (HPAP), which can be
detected by histochemical staining. After a pulse of tamox-
ifen that converted about 30% of β cells in young mice to cells that express HPAP, the investigators followed the per-
centage of labeled β cells for a year, during which time the
total number of β cells in the pancreas increased by 6.5-
fold. How do you suppose the percentage of β cells would
change over time if new β cells were derived from stem
cells? What if new β cells were derived from preexisting
β cells? Which hypothesis do the results in Figure Q22–2
support?
Step by step
Solved in 2 steps
