PGE₂ increases the proliferation of SKL cells in vitro and in vivo. (A) Lin^neg cells were treated with either vehicle or 1 μM dmPGE₂ for 2 hours, washed, and cultured in media with rmSCF, rhFlt3, and rhTpo. After 20 hours, cells were stained for SKL and Hoechst-33342 and Pyronin-Y. The proportion of SKL cells in cell cycle was quantitated by FACS. Representative flow plot showing cell-cycle distribution of gated SKL cells and combined data for fold increase in cell cycle for dmPGE₂-treated cells compared with vehicle control from 3 experiments; mean plus or minus SEM; n = 9 mice, each assayed individually. (B) CD45.1 Lin^neg bone marrow cells were treated with dmPGE₂ or vehicle and transplanted into lethally irradiated CD45.2 mice. Immediately after transplantation, BrdU was provided in drinking water and administered by intraperitoneal injection. Bone marrow was analyzed 16 hours later and the proportion of CD45.1⁺, SKL cells that was BrdU⁺ was analyzed by FACS analysis. Data are mean plus or minus SEM; n = 5 per mice/group, each assayed individually.