, 2009). An analogous mechanism may be controlling NFIA expression during astro-glial development. Another key consideration in our understanding of the transcriptional mechanisms controlling the induction of NFIA is the role of epigenetics. Chromatin-modifying factors, PcG genes Ring1b and Ezh2, have been implicated in the repression of neurogenesis, a key JQ1 molecular weight process in the gliogenic switch, in the embryonic cortex, and DNA methylation has been implicated in
regulating the expression of GFAP during astrocyte differentiation ( Fan et al., 2005, Hirabayashi et al., 2009 and Takizawa et al., 2001). Future studies will be aimed at examining the link between epigenetic modifiers and NFIA induction. Biochemical studies demonstrate that NFIA and Sox9 physically associate and collaborate to induce the expression of a subset of genes just after the initiation of gliogenesis. Given that Sox9 function is associated with neural stem cell maintenance, initiation of gliogenesis, and various aspects of glial differentiation during CNS development, its interaction with NFIA GSK1210151A molecular weight may mediate
a subset of these diverse roles. Although Sox9 induction of NFIA may trigger the generation of glial fates, it does not result in a loss of neurogenic potential from these populations, as Sox9 expression is required at these stages for neurosphere formation in vitro, and NFIA is not sufficient to suppress neurogenesis (Deneen et al., 2006 and Scott et al., 2010). Therefore,
we propose a model whereby Sox9 function during the gliogenic switch evolves from maintaining neural stem cells and initiating gliogenesis (E10.5–E11.5) to promoting glial lineage progression (E11.5–E12.5) by controlling a set of genes that contribute to early gliogenesis (Figure 8). This shift in Sox9 function during glial lineage progression is facilitated by a feedforward mechanism, where Sox9 induces NFIA expression during glial initiation and subsequently associates with NFIA to drive lineage progression. Hence, Sox9 coordinates glial initiation and glial lineage progression via regulation and association with NFIA, respectively. Our rescue analysis of targets of the Sox9/NFIA complex found that these genes restore panglial second or ASP-specific identity during gliogenesis. The role of this complex in ASP formation is supported by specific defects at later developmental stages in astrocyte differentiation in both Sox9 and NFIA knockout mice (Deneen et al., 2006 and Stolt et al., 2003). That this complex appears to influence ASP development raises the question of whether it also has a specific role in oligodendrocyte precursor (OLP) development. Given that both NFIA and Sox9, and the targets we identified, are also expressed in OLPs, it is possible that a subset of their targets specifically contribute to OLP development.