The origin of new cells of the pancreasfrom stem cells or from preexisting cellswas not

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 tamoxifen that converted about 30% of β cells in young mice to cells that express HPAP, the investigators followed the percentage 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?

Figure Q22-2

Transcribed Image Text:

100 80 60 40 20 0 4 6 9 12 months after tamoxifen injection percent of ß cells expressing HPAP