Neutral sphingomyelinase activity regulates HSPC pool composition. (A) Relative Smpd3 gene expression across murine HSPC subpopulations in vivo. HSC and MPP (B), oligopotent progenitor proportions (C), and relative Smpd3 gene expression (D) after 14-day ex vivo culture. HSC and MPP (E) or oligopotent progenitor proportions in ex vivo culture 1 day after 24-hour GW4869 treatment (F). (G) HSC and MPP proportions 7 days after 24-hour GW4869 treatment. PLS-DA plot (H), variable importance in projection (VIP) plot (I), and heat map of top 50 differentially expressed lipids across HSPCs after GW4869 treatment (J). (K) Exemplary SM, ceramide (Cer), and hexosylceramide (Hex1Cer) levels in HSPCs over time. Refer to supplemental Figure 2.