Fig. 4
Cell cycle analyses of day 10 and day 21 tail blastemas after proximal and distal amputations reveal specific growth fractions and uniform cell cycle lengths. a–d. Representative photomicrographs of 10 day-proximal (a), 10 day-distal (b), 21 day-proximal (c) and 21 day-distal (d) blastemas, each cumulatively labeled for 105 h. a–b. Essentially all cells in both mesenchymal blastemas are BrdU+. c–d. The majority of nuclei in the 21 day-proximal-mesenchymal blastema (c.) but only a minority in the 21 day-distal-mesenchymal blastema (d.) are still positive for BrdU. e–f. BrdU labeling index (dimensionless fraction of BrdU+ cells) as time courses of cumulative BrdU treatment starting at day 10 (e.) and day 21 (f.). Each data point represents an individual animal (three to five per time point). Solid curves show best-fitting proliferation models (see Methods). g–h. Cell cycle parameters derived from model fits to the time courses of the BrdU labeling index. g. The cell cycle lengths T C (all parameters reported as mean ± 68 % confidence interval) of all four conditions are very similar with T C = (103 ± 26) hours for 10 day-proximal, T C = (112 ± 29) hours for 10 day-distal, T C = (119 ± 47) hours for 21 day-proximal and T C = (84 ± 38) hours for 21 day-distal blastemas, none of the differences is statistically significant. The S-phase duration T S also was very similar for all four conditions with T S = (54 ± 17) hours for 10 day-proximal, T S = (45 ± 14) hours for 10 day-distal, T S = (42 ± 17) hours for 21 day-proximal and T S = (43 ± 28) hours for 21 day-distal blastemas. h. The fraction of proliferating mesenchymal cells (GF) decreased significantly from day 10 to 21 (p < 0.001 for distal and p < 0.05 for proximal blastemas) and at day 21 was significantly lower for distal than for proximal blastemas (p < 0.001) with GF = (95 ± 2) % for 10 day-proximal, GF = (97 ± 3) % for 10 day-distal, GF = (69 ± 10) % for 21 day-proximal and GF = (36 ± 3) % for 21 day-distal blastemas. Scale bars in (a–d), 100 μm