ALCAM^-Sca-1⁺ MPCs enhance the colony-forming capacity of HSPCs after stimulation with dmPGE₂ or the EP4 agonist. (A-D) Expression of EP receptors in endosteal cell fractions. The expression of the PGE₂ receptors (A) Ep1, (B) Ep2, (C) Ep3, and (D) Ep4 in each fraction was analyzed. All EP receptors were highly expressed in ALCAM^–Sca-1⁺ MPCs compared with the other fractions. The ALCAM^–Sca-1^– fraction served as the reference sample. Actb was used to normalize target gene expression. Data represent means ± SD (*P < .01; **P < .05, n = 3). Representative data from 2 independent experiments are shown. (E) Digital Array analysis of Ep1, Ep2, Ep3, and Ep4 expression in ALCAM^–Sca-1⁺ MPCs (400 cells/sample). The numbers of estimated target genes are shown. Data represent means ± SD (*P < .01, n = 3). Representative data from 2 independent experiments are shown. (F) Effect of dmPGE₂ on HSPCs via endosteal cells. LSK cells were cocultured with drug-stimulated endosteal cell populations, and the colony-forming capacity was evaluated. Numbers of CFU-Cs and HPP-CFCs are shown. Data represent means ± SD (*P < .05, n = 3). Representative data from 2 independent experiments are shown. (G and H) The effects of dmPGE₂ and other EP4 agonists on the formation of CFU-Cs and HPP-CFCs from LSK cells after coculture with ALCAM^–Sca-1⁺ MPCs. Numbers of CFU-Cs (G) and HPP-CFCs (H) are shown. Data represent means ± SD (*P < .05, n = 3). Representative data from 3 independent experiments are shown.