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P.710 left column 2nd paragraph: "The cell cycle activity of HSCs over the lifetime of an organism is equally dynamic, and reflects the needs of the organism at
different developmental stages. During fetal life, the central function of HSCs is to rapidly generate homeostatic levels of blood cells for oxygen transport and immune system development in the growing organism. In line with this role, between 95 and 100% of HSCs are actively cycling in the mouse fetal liver with a cell cycle transit time between 10–14 h (Fig. 1, Bowie et al., 2006, Nygren et al., 2006)." P.710 left column bottom paragraph: "Remarkably, the BM [bone marrow] HSC population rapidly switches to a quiescent state by 4 wk of age, with only ~5% of total HSCs actively in the cell cycle (defined as S, G2, or M phases) thereafter through adult life (Cheshier et al., 1999, Bowie et al., 2006, Kiel et al., 2007) (Fig. 1)." P.710 right column 2nd paragraph: "Interestingly, adult HSCs are not uniformly dormant. In vivo experiments assessing cell cycle activity (by measuring retention of BrdU or histone 2B (H2B)-GFP expression pulses) in mature HSCs suggest a notable heterogeneity in the degree to which HSCs are quiescent (Wilson et al., 2008, Foudi et al., 2009). These studies propose the subfractionation of the HSC
compartment into “dormant” and “activated” phenotypes with distinct rates of cell cycle entry, comprising ~5–10% and 90–95% of the HSC pool, respectively (Fig. 1)." See caption to figure 1 |