Asymmetry of HSC expansion and maintenance divisions stimulated by 20 ng/mL IL-11 plus either 10 ng/mL or 300 ng/mL SF. (A) Single-cell cultures of CD45^midlin⁻Rho⁻SP cells were monitored every 4 hours to determine when a first division took place. Between 4 and 8 hours after the first mitosis, doublets were separated and each of the 2 cells injected into a separate recipient with the resulting division type shown. SR indicates self-renewal; SF, Steel factor. (B) The distribution of HSC subtypes is detailed in the cases where at least one of the 2 daughter cells repopulated an irradiated recipient. (C) Fluorescence-activated cell sorter plots for a pair of repopulated mice transplanted 16 weeks earlier with individual cells from one separated daughter pair.