%0 Generic
%A Shi, Yan
%D 2015
%F heidok:18941
%R 10.11588/heidok.00018941
%T Regulation of Adult Neural Stem Cell Activation  by Orphan Nuclear Receptor TLX (NR2E1)  and Notch Signaling
%U https://archiv.ub.uni-heidelberg.de/volltextserver/18941/
%X The adult mammalian brain contains neural stem cells (NSCs) that continue to generate  neurons throughout adulthood, a process referred to as neurogenesis. Adult NSCs are  relatively quiescent and undergo cell division only when they are activated to reenter the cell  cycle. Two types of quiescent NSCs have been previously identified, which can be  distinguished on the basis of differential expression of Prominin-1 (Pro). Upon activation and  asymmetrical division, a NSC self-renews and gives rise to a transit-amplifying precursor  (TAP), which will rapidly divide while differentiating into neuroblasts. Our group has developed  an approach based on fluorescence activated cell sorting (FACS) to purify quiescent NSCs  (qNSCs), activated NSCs (aNSCs) and TAPs.  We have previously shown that in adult NSCs the orphan nuclear receptor Tailless (Tlx,  NR2E1) is essential for promoting cell cycle entry and the transition from qNSCs to aNSCs.  Therefore, mice lacking Tlx expression (Tlx-/-) represent a nice model system to investigate the  mechanisms underlying NSC activation. To further understand the molecular mechanisms  underlying the effect of TLX on NSC activation I have compared gene expression in NSCs  isolated from wild type (WT) and Tlx-/- mice. This analysis revealed an upregulation of Hes1  expression and a significant change in the expression of several genes associated to the  Notch pathway in both Pro+ and Pro- mutant qNSCs. Moreover, in the absence of TLX, the  nuclear localization of the Notch intracellular domain (NICD) was increased in Pro- qNSCs,  suggesting hyper activation of the canonical Notch pathway, which may prevent cell cycle  entry. To provide support for this hypothesis, I have investigated the effect of pharmacological  inhibition of Notch signaling on NSC activation. These experiments revealed that indeed  blockade of Notch signaling increased proliferation of both WT and Tlx-/- precursors. They also  showed that inhibition of Notch signaling leads to the generation of Pro+ qNSCs from the Procell  pool, suggesting a lineage relationship between the two groups of qNSCs. Since TLX is  a transcriptional repressor, it may modulate Notch signaling by repressing the expression of  Hes1. To further investigate this hypothesis I have taken advantage of luciferase and  chromatin immunoprecipitation (ChIP) assays and I was able to show that TLX represses  Hes1 expression and that this effect requires the presence of the RBPJ binding site.  Taken together, my results have uncovered a previously unknown function of TLX in the  regulation of Hes1 expression, which affects the activation of the canonical Notch pathway in  NSCs and also the progression from Pro- to Pro+ qNSCs.