CSF generated neurospheres from adult SVZ precursors as well (Figure 4I). Consistent with these observations and our explant studies,
the Igf1R inhibitor picropodophyllin blocked the formation of spheres in the presence of E17 CSF Anticancer Compound Library research buy (data not shown). Our data suggest that the choroid plexus is the most prominent source of Igf2 in CSF (Figures 3 and S3A). Accordingly, media conditioned with E17 choroid plexus provided enhanced support for neurosphere formation compared to media conditioned with embryonic cortex, adult choroid plexus, or adult brain (Table S3), demonstrating that one or more factors actively secreted from the embryonic choroid plexus, including potentially Igf2, is sufficient for stem cell growth and maintenance. Thus, distinct factors secreted by the choroid plexus into the embryonic Roxadustat concentration CSF, including Igf2, confer E17 CSF with an age-associated advantage to stimulate and maintain
neural stem cell proliferation, and Igf signaling is likely one pathway that promotes this process. Mouse explant experiments confirmed a requirement for Igf signaling in the proliferation of progenitor cells. Mouse embryonic CSF supported the survival and proliferation of mouse cortical progenitors (C57BL/6 explants: 20% ACSF in NBM mean, 7.4 ± 0.2; 20% E16.5 CSF in NBM mean, 14.1 ± 1.4; Mann-Whitney; p < 0.01; n = 3), and purified Igf2 in 20% ACSF in NBM stimulated cortical progenitor proliferation (Figure 5A). When the Igf1R was genetically inactivated in cortical progenitors (Igf1RloxP/loxP/NestinCre+/−) ( Liu et al., 2009), wild-type CSF no longer stimulated cortical progenitor proliferation (ACSF, 17.6 ± 2.9; E16.5 CSF, 16.4 ± 3.0; Mann-Whitney; N.S.; n = 3). Importantly, CSF obtained from Igf2−/− mice failed to stimulate progenitor proliferation in wild-type second explants compared to control ( Figure 5B), suggesting that Igf2 in its native CSF environment stimulates proliferation of progenitor cells during cerebral cortical development. As expected for the roles we have shown for Igf2 in regulating proliferation, we found that Igf2-deficiency reduced brain size ( Figure 5C).
Igf2−/− brain weight decreased by 24% at P8 compared to controls ( Figure 5D). Accordingly, the overall cortical perimeter and surface area were reduced in Igf2−/− brains compared to controls as well ( Figures 5E–5G). Profound defects in somatic size couple to brain size ( Purves, 1988). As previously reported ( DeChiara et al., 1991 and Baker et al., 1993), Igf2−/− body weight was reduced compared to control (mean body weight (g) at P8: Igf2+/+, 5.6 ± 0.01; Igf2−/−, 2.8 ± 0.1; Mann-Whitney; p < 0.0001; n = 11), suggesting that Igf2 may be a secreted factor that scales brain size to body size. Consistent with the mouse CSF Igf2 expression pattern that is significantly increased during later embryonic development ( Figure S3B), blunting Igf2 expression markedly reduced the proliferating progenitor cells at E16.