The goal of this study is to identify novel molecular regulators that preserve the ability of neural stem cells (NSCs) to self-renew and produce new neurons in the brains of aged individuals. Adult NSCs play key roles in learning, memory, and response to injury in young adults, but their function declines with age. The molecular mechanisms that prevent the decline in NSC function during aging are largely unknown. I will use an innovative approach to identify such regulators in an unbiased manner. Widespread (broad) domains of histone H3 lysine 4 trimethylation (H3K4me3) have been recently proposed to mark molecules with key functions in embryonic, adult hematopoietic and skin stem cells. My project uses this broad H3K4me3 domain signature as a discovery tool to identify new regulators of adult NSC function. In preliminary experiments, I identified the genome-wide landscape of H3K4me3 in adult primary cultures of NSCs from young mice using chromatin immunoprecipitation coupled with high throughput sequencing (ChIP-Seq). Consistent with work in other stem cell types, I observed the presence of broad H3K4me3 domains at the genomic loci encoding known NSC regulators. Interestingly, I found that the broadest H3K4me3 domains are present at the genomic loci of long non-coding RNAs (lncRNAs), raising the exciting possibility that lncRNAs could be key regulators of NSC function. I found that one of these lncRNAs, Lnc15, declines with age in the NSC niche in vivo and is required for NSC self-renewal in vitro. Based on my preliminary data, I hypothesize that Lnc15 functions to preserve the proliferative and neurogenic potential of adult NSCs and that Lnc15 function declines with normal aging. I will test this idea by examining the regulation and expression of Lnc15 in NSCs and differentiated progeny during aging, using a combination of in vitro NSC cell culture, NSCs freshly purified from the brain by fluorescence-activated cells sorting (FACS), and immunostaining on intact brain sections. I will also examine the molecular mechanisms that regulate Lnc15 expression during aging. In parallel, I will assess the functional role and mechanism of action of Lnc15 in proliferation and differentiation of young and old NSCs by viral-mediated knockdown and overexpression in vitro and in vivo. Once I delineate the role of Lnc15 in aging NSCs, I will explore its mechanism of action in these cells. Together these studies will provide new insight into the regulation and functional importance of Lnc15 in young and old NSCs, and, more generally will highlight the importance of broad H3K4m3 domains in adult stem cell aging. Understanding the mechanisms that preserve youthful NSC state be critical for identifying new avenues for preserving or reactivating the pool of NSCs during aging, which will have important implications for slowing or preventing age-related cognitive decline.