Impact of Notch signaling inhibition on OB-mediated enhancement of HPC function. Increase in total cell number from the original 1000 LSK cells (A) and production of CFU (B) in cocultures of OB, SC, and LSK cells with and without the Notch inhibitor, GSI. Cell numbers and CFU content were assayed, and fold increase was calculated to day 0 values. Data shown are from 1 of 3 independent experiments with similar results. GSI was added at 10nM on day 0 and replenished twice during the next 7-day culture period. #P < .01, comparisons within each group between treatments with and without GSI. +P < .01 compared with OB + LSK group without GSI. *P < .05 compared with OB + LSK with GSI.