Although Igf2 availability decreased in adult CSF (Figures 3C and S3B), Igf2 continued to be expressed in adult choroid plexus (data not shown) and maintained adult neurospheres ( Figure 4I), suggesting that low levels of CSF Igf2 contribute to the maintenance of adult neural stem cells. The aberrant increase in Igf2 in advanced GBM patients reinforces the hypothesis that Igf signaling has an influence on proliferation of cortical precursors. Our identification of Igf2 regulation

of neurogenesis and brain size complements a literature in which Igf signaling is well known to influence body and brain size ( Baker et al., 1993, DeChiara et al., 1991 and Purves, 1988), raising Selleckchem VX-770 the intriguing possibility that Igf2 represents a secreted factor that may scale brain size to body size. The activity of growth promoting factors in the CSF and their action on progenitors across the apical surface may be a model for other epithelia including lung, gut, and vascular endothelia that develop in relation to extracellular fluids (Bendall et al., 2007 and Scadden, 2006). Extracellular

fluid apparently regulates the microenvironment of hematopoietic stem cells, where Igf signaling regulates progenitor proliferation (Orkin and Zon, 2008 and Zhang and Lodish, 2004). The differential capacity of Igf signaling to confer a proliferative advantage to stem cells may be regulated in part by Igf’s interactions with binding proteins Androgen Receptor Antagonist cell line or other secreted factors in the environment (Clemmons, 1997). Our experiments focused on the age-associated effects of CSF on survival and proliferation across the cortical ventricular zone. However, STK38 the distribution of CSF resident proteins, as well as the flow of the CSF, may also influence ciliary orientation and maturing ependymal cell polarity (Mirzadeh et al., 2010), which create activity gradients as has been shown for Slit (Sawamoto et al., 2006). If a major component of the stem cell niche reflects secreted factors

acting at long distances from their sources, modulation of the proteomic composition of extracellular fluids may also provide unexpected ways to regulate stem cell behavior in health and disease. For example, while Igf2 activity peaked in embryonic CSF, some CSF-borne Igf persisted in adulthood (Figures 3, S3B, and data not shown). Igf2 and Igf1 in adult CSF may contribute to the retention of neural stem cell properties in the adult SVZ (Doetsch et al., 1999). Importantly, the regulation of CSF growth factors may also extend to pathologic states. Igf2 and other diffusible growth factors that drive neural progenitor proliferation during development are upregulated in some GBM patients (Louis, 2006 and Soroceanu et al., 2007), and GBM patients have elevated Igf2 levels in their CSF.