P3 cells proliferate in the blastema.

<p>A–C) GFP and Ki67 co-immunohistochemical reveal P3 isolated cells engraft and proliferate. A) GFP labeled P3 cells are identified within the digit. B) Ki-67, a marker for proliferation, is expressed in engrafted and endogenous P3 cells. C) Merged GFP and Ki67 expression identifies a fraction of engrafted P3 cells that are proliferating. Double labeled cells shown in C are indicated with arrows in the image set. GFP- red, Ki67- green, DAPI nuclear stain- blue. Scale bar = 50 µm. D) Quantification of the proliferation indices of P2 and P3 engrafted cells compared to endogenous neighboring cells. Left: In unamputated digits 17 days post engraftment, P3 cells proliferated at a rate similar to neighboring control cells, whereas P2 cells are non-proliferative. Right: P3 cells participating in blastema formation at 10 DPA display a proliferation index that was lower than neighboring endogenous cells but significantly higher than P2 cells within the blastema. All chart values are expressed as means ± SEM. The proliferative index of P3 cells is significantly greater than P2 cells in both studies (**, p-value <0.005).