M40^−/− HSCs show enhanced signaling in response to Tpo. Purified LSK cells from WT and M40^−/− mice were starved and stimulated for 10 minutes with 1 or 10 ng/mL Tpo. Lysates from LSK cells were resolved on Tris-Glycine gels and blots were probed with antibodies specific for phosphorylated and total JAK2, Stat5, and Akt proteins. The ratios of phosphoprotein to total protein levels are indicated on top of individual bands.