Ars2 maintains neural stem cell identity via direct transcriptional activation of Sox2

Fundamental questions concern the transcriptional networks that control the identity and self-renewal of neural stem cells (NSCs), a specialized subset of astroglial cells endowed with stem properties and neurogenic capacity. We observed that the zinc finger protein Ars2 is expressed by adult NSCs from the subventricular zone (SVZ). Selective knockdown of Ars2 in GFAP(+) cells within the adult SVZ depleted NSC number and their neurogenic capacity. These phenotypes were recapitulated in the postnatal SVZ of hGFAP-Cre::Ars2(fl/fl) conditional knockouts, but were more severe. Ex vivo assays showed that Ars2 was necessary and sufficient to promote NSC self-renewal, by positively regulating the expression of Sox2. Although plant(1–3) and animal(4,5) orthologs of Ars2 are known for their conserved roles in microRNA biogenesis, we unexpectedly observed that Ars2 retained capacity to promote self-renewal in Drosha and Dicer knockout NSCs. Instead, chromatin immunoprecipitation revealed that Ars2 bound a specific region within the 6kb NSC enhancer of Sox2. This association was RNA-independent, and the bound region was required for Ars2-mediated activation of Sox2. We used gel-shift analysis to confirm direct interaction, and to refine the region bound by Ars2 to a specific conserved DNA sequence. The importance of Sox2 as a critical downstream effector was shown by its ability to restore the self-renewal and multipotency defects of Ars2 knockout NSCs. Altogether, we reveal Ars2 as a novel transcription factor that controls the multipotent progenitor state of NSCs via direct activation of the pluripotency factor Sox2.