Effect of ectopic PU.1 expression on the number of colonies derived from BM cells. (A) Noninfected murine BM cells (□) or cells infected with PU.1 (LXSN-PU.1) (▧), the c-myb transactivation domain in antisense orientation (LXSN-mybTAS) (▪), or the insert-less (LXSN) () retroviral constructs. After 48 hours, 2.5 × 10⁴ cells were plated in methylcellulose in the presence of the indicated growth factors. Colonies were counted 10 days later. Error bars indicate ± SD for three independent experiments. (B) Photomicrographs of G-CSF–derived BM colonies.