Endothelial expression of mKITL is required for sustaining normal levels of circulating sKITL but not BM HSCs in adult mice. (A-B) qPCR analysis of Kitl mRNA levels using Kitl exon 2-3–spanning (measuring total Kitl mRNA) and exon 7-8–spanning (measuring mRNA generating mKITL) amplicons in FACS-purified BM ECs (A) and LEPR⁺ PVCs (CD45^–TER119^–CD31^–SCA1^–LEPR⁺) (B) from 13- to 15-week-old Tie2ΔEx7 (n = 5), Tie2,LepRΔEx7 (n = 5-6) and wild-type littermate control (n = 3) mice. (C) sKITL levels measured by ELISA in the blood serum from 13- to 15-week-old wild-type (control, n = 10), Tie2ΔEx7 (n = 14) and Tie2,LepRΔEx7 (n = 14) mice. (D) sKITL levels measured by ELISA in the BM extracellular fluid from 13- to 15-week- old wild-type (control, n = 3), Tie2ΔEx7 (n = 5), and Tie2,LepRΔEx7 (n = 5) mice. (E-G) Mean (± SEM) number (E) and frequency (F) of LSK CD150⁺CD48^– HSCs, and number of committed myelo-erythroid progenitor cells (G) from 2 femurs and 2 tibias of 13- to 15-week-old wild-type (control; n = 7), Tie2ΔEx7 (n = 11), and Tie2,LepRΔEx7 (n = 8) mice. All data represent mean ± SEM, the nonparametric Mann-Whitney test was used to assess statistical significance. ∗P < .05; ∗∗P < .01; ∗∗∗P < .001.