Mean number of progenitors ± SEM per 10⁵ marrow cells cocultured on GpE86-Neo or GpE86-Mpl-R cells. Cocultured cells were grown (A) in methylcellulose in the presence of IL-3 + EPO to reveal CFU-GEMM, BFU-E, and CFU-GM or in agar in the presence of pokeweed mitogen spleen cell conditioned medium (SCM) to reveal CFU-MK with (+) or without (−) G418 (n = 4); or (B) in methylcellulose (CFU-GEMM, BFU-E, and CFU-GM) or in agar (CFU-MK) in the presence of TPO (n = 4) with (+) or without (−) G418.