A subset of BM endothelial cells exhibit bright green fluorescence in mice that carry the Fgf23^eGFP allele. Fluorescence-activated cell sorter plots of BM cells from Tmprss6^–/–Fgf23^+/eGFP, Tmprss6^+/−Fgf23^+/eGFP, Tmprss6^–/–Fgf23^+/+, and Tmprss6^+/−Fgf23^+/+ male littermates (18 weeks old). The numbers represent the percentage of each gated population. Forward scatter (FSC) and side scatter (SSC) were used to exclude debris and cell doublets, and eGFP^bright cells were assessed in each single-cell population (green gate). BM endothelial cells were identified as the CD45^-TER-119^-CD31⁺ population (magenta gate) as described,⁴¹ using CD31 antibody clone 390, and eGFP fluorescence was assessed in the endothelial cell gate. A total of 6 × 10⁵ BM cells per mouse were analyzed.