Impaired neural migration and defects

Impaired neural migration and defects in the order glp-2 cytoskeleton are well-known factors contributing to malformations during the cortical development (Pang et al., 2008). Reduced expression of NSUN2 in human NES cells impaired migration toward the chemoattractant FGF2. FGF2 is widely used to maintain neural progenitors in long-term culture (Ostenfeld and Svendsen, 2004), is crucial for normal brain development, and is highly expressed in the ventricular zone when neural progenitors are formed (Dono et al., 1998; Vaccarino et al., 1999). Interestingly, injection of FGF2 into the mouse cerebral ventricles at E14 in utero did not affect the alignment of the cerebral neuronal layers; however, both cell number and cell density of the upper layers (II/III) and the lower layers (IV–VI) of the cerebral cortex were increased (Ohmiya et al., 2001).
Experimental Procedures
Author Contributions
Acknowledgments We thank everybody who provided us with reagents, in particular Austin Smith for providing the neuroepithelial stem cell lines and Anna Falk for advice on their culture. This work was funded by Cancer Research UK (CR-UK C10701/A15181), Worldwide Cancer Research (15-0168), the Medical Research Council (MRC MR/M01939X/1), the European Research Council (ERC 310360), and EMBO. Research in M.F.\'s laboratory was supported by a core support grant from the Wellcome Trust and MRC to the Wellcome Trust-Medical Research Cambridge Stem Cell Institute.
Introduction It has been widely postulated that a specific sub-population of glioblastoma (GBM) cells exhibit stem-like properties and that they underlie treatment resistance and recurrence due to their ability to survive DNA-damaging treatments and repopulate the tumor (Mannino and Chalmers, 2011). This population is dynamic and can be altered by specific growth conditions, including exposure to serum and bone morphogenic proteins (BMP), which render them non-tumorigenic (Piccirillo et al., 2006). These cells cannot be defined by a single marker, but the phenotype is enriched in Promonin1 (PROM1, known as CD133), SRY-box2 (SOX2) and Nestin (NES)-positive cells. The role of individual markers in contributing to the phenotype remains uncertain, but, for example, SOX2 has been functionally implicated in a rapidly proliferating, self-renewing population, and with maintenance of the undifferentiated state. Individual markers have rarely been shown to predict radioresistant sub-populations (Balbous et al., 2014; Berezovsky et al., 2014; Lemke et al., 2014). Upregulated DNA damage responses (DDRs) have been documented in glioblastoma stem cells (GSCs) including enhanced checkpoint signaling and recruitment of repair proteins (Bao et al., 2006; Cheng et al., 2011; Facchino et al., 2010; Zeppernick et al., 2008); however, the mechanisms underlying resistance to treatment are not fully understood. More importantly, it is not clear how specific resistance mechanisms align with the established phenotypic characteristics that drive recurrence or with marker positivity. Therefore, it remains unclear which repair pathways are the most relevant targets in GSCs. Overexpression of the DNA repair protein, RAD51, the central protein involved in homologous repair (HR) of DNA double-strand breaks (DSBs), has been documented in glioma and numerous other cancers (Hannay et al., 2007; Maacke et al., 2000; Mehrara et al., 2007; Tennstedt et al., 2012; Welsh et al., 2009). Previously, we reported that targeting RAD51 using small interfering RNA-radiosensitized established glioma cell lines, and recent data confirm that targeting HR is more effective at radiosensitizing GSCs than inhibiting the major alternative DSB repair pathway, non-homologous end-joining (NHEJ) (Lim et al., 2014; Short et al., 2011). Inhibition of HR can be achieved through modulating expression, inhibiting nuclear translocation, or preventing DNA binding of RAD51, and small-molecule inhibitors have been developed, including B02 and RI-1. B02 impairs the RAD51-single-stranded DNA interaction at the primary site of RAD51 during nucleoprotein filament formation and at its secondary DNA binding site, where double-stranded DNA attaches during the search for homologous DNA (Huang et al., 2012). This agent displays synergy with the DNA crosslinking agent cisplatin, which requires HR for DNA repair (Huang and Mazin, 2014). RI-1 possesses a chloromaleimide moiety, which covalently binds to the thiol group in the cysteine at position 319 and occupies the interface between monomeric RAD51 proteins as well as an ATP binding loop. This alters RAD51-ATP interactions and subverts RAD51-RAD51 binding and polymerization, which is essential for filament elongation. RI-1 is synergistic with mitomycin C and both RI-1 and B02 are radiosensitizers (Budke et al., 2012a, 2012b; Huang and Mazin, 2014; Huang et al., 2012; Ward et al., 2015).