Adult mLNSCs derive from FAP⁺ cells in the e15.5 iLN anlage. (A) FC^Tomato and littermate C^Tomato mice were kept on dox from different stages of embryogenesis until analysis at 4 wk. (B and C) The proportion of tdTomato⁺ mLNSCs in iLNs fate-mapped from different stages of embryogenesis. Statistical significance was determined using a two-tailed t test, comparing FC^Tomato to C^Tomato littermates: *, P < 0.05; ***, P < 0.001; ns, not significant. (D and E) The LN tdTomato⁺ area was determined in iLNs fate-mapped from different stages of embryogenesis. Scale bars, 500 µm. Images represent two to five individual mice combined from two to three experiments. Statistical significance was determined using a two-tailed t test, comparing FC^Tomato mice to C^Tomato littermates: **, P < 0.01; ***, P < 0.001. (F and G) tdTomato⁺ FDCs (F) and MRCs (G) in iLNs fate-mapped from e14.5 and e15.5. Images represent three to five mice. Scale bars, 50 µm. (H–J) The proportion of FDCs (H) and MRCs (I) labeled in adult iLNs fate-mapped from embryogenesis. Data represent three or more follicles per mouse, combined from three to five mice in two experiments. Statistical significance was determined by one-way ANOVA, comparing to no dox: ****, P < 0.0001. (J) Proportion of FDCs and MRCs that are tdTomato⁺ in FC^Tomato (+dox e14.5) mice. Statistical significance was determined using a Mann–Whitney U test. (K) tdTomato labeling in MRCs and FDCs fate-mapped from e14.5. Arrows and arrowheads indicate tdTomato⁺ and tdTomato⁻ cells, respectively. Scale bar, 50 µm. White boxes indicate enlarged areas. Images represent three to five mice compiled from two experiments.