Figure 3.

MEC Cell Lineage Tracing in the LG of the SMA^CreERT2:R26-Confetti Mice

(A) Schematic diagram of the experimental design. SMA^CreERT2:R26-Confetti mice were injected with TM at P14, and LGs were analyzed 1, 5, and 30 weeks later. Similarly, adult mice were injected with TM at P65, and LGs were excised and studied 1 and 15 weeks later.

(B) Labeling efficiency after TM administration at P14 (determined in 1 week after TM injection).

(C and F) Mosaic labeling of MECs 1 week after TM administration. (C) Low magnification image showing many labeled MECs. MECs still have an immature phenotype, i.e., their processes are short and thick (F).

(D, E, G, and H) (D and G) After 5 weeks MECs form well-distinguishable clones. Thirty weeks later MEC clone size varies from being small (E and H, green clone), i.e., consisting of 1–5 cells, to large (H), consisting of 32–50 cells (red clone), suggesting the existence of short- and long-term proliferating cells within the MEC lineage.

(I) Quantification of MEC clones after TM administration at P14. Results show mean ± SD, p < 0.0001, as determined by the Wilcoxon-signed rank test.

(J–M) (J) MECs labeled at P65 show mature phenotype but low labeling efficiency (K) (GFP [bright green], nuclear; YFP [green], cytoplasmic; and dsRed [red], cytoplasmic), as determined at 1 week after TM administration. 15 weeks after TM administration only small clones consisting of 1–4 cells were detected in adult SMA^CreERT2:R26-Confetti mice (L and M). MECs in (L) were immunostained for αSMA.