Project description:Quiescence is essential for the long term maintenance of adult stem cells and tissue homeostasis. However, how stem cells maintain quiescence is still poorly understood. Here we show that stem cells in the dentate gyrus of the adult hippocampus actively transcribe the proactivation factor Ascl1 regardless of their activation state. We found that the inhibitor of DNA binding protein Id4 suppresses Ascl1 activity in neural stem cell cultures. Id4 sequesters Ascl1 heterodimerisation partner, promoting the degradation of Ascl1 protein and neural stem cell quiescence. Accordingly, elimination of Id4 from stem cells in the adult hippocampus results in abnormal accumulation of Ascl1 protein and premature stem cell activation. We also found that multiple signalling pathways converge on the regulation of Id4 to control the activity of hippocampal stem cells. Id4 therefore maintains quiescence of adult neural stem cells, in sharp contrast with its role of promoting the proliferation of embryonic neural progenitors.
Project description:Adult hippocampal neurogenesis is important for certain forms of cognition and failing neurogenesis has been implicated in neuropsychiatric diseases. The neurogenic capacity of hippocampal neural stem/progenitor cells (NSPCs) depends on a balance between quiescent and proliferative states. However, how this balance is regulated remains poorly understood. Here we show that the rate of fatty acid oxidation (FAO) defines quiescence vs. proliferation in NSPCs. Quiescent NSPCs show high levels of carnitine palmitoyltransferase 1a (Cpt1a)-dependent FAO, which is downregulated in proliferating NSPCs. Pharmacological inhibition and conditional deletion of Cpt1a in vitro and in vivo leads to altered NSPC behavior, showing that Cpt1a-dependent FAO is required for stem cell maintenance and proper neurogenesis. Strikingly, experimental manipulation of malonyl-CoA, the metabolite that regulates levels of FAO, is sufficient to induce exit from quiescence and to enhance NSPC proliferation. Thus, the data presented here identify a shift in FAO metabolism that governs NSPC behavior and suggest an instructive role for fatty acid metabolism in regulating NSPC activity.
Project description:Quiescence acquisition of proliferating neural stem cells (NSCs) is required to establish the adult NSC pool yet the underlying molecular mechanisms are not well-understood. Here we showed that conditional deletion of the m6A reader Ythdf2, which promotes mRNA decay, in proliferating NSCs in the early postnatal mouse hippocampus led to elevated quiescence acquisition with decreased neurogenesis. Multimodal profiling of m6A modification, YTHDF2 binding, and mRNA decay in hippocampal NSCs identified shared targets in multiple TGFβ signaling pathway components, including TGFβ ligands, maturation factors, receptors, transcription regulators, and signaling regulators. Functionally, Ythdf2 deletion led to TGFβ signaling activation in NSCs, suppression of which rescued elevated quiescence acquisition of proliferating hippocampal NSCs. Our study reveals the dynamic nature and critical roles of mRNA decay in establishing the quiescent adult hippocampal NSC pool and uncovers a novel mode of epitranscriptomic control via co-regulation of multiple components of the same signaling pathway.
Project description:We have characterized the transcriptome of adult rat hippocampal neural stem and progenitor cell (NSPC) cultures. The NSPCs cultures can be reversibly arrested by the quiescence-promoting signal BMP4. We provide expression data from NSPCs grown as neurospheres for 4 days in vitro in the presence of FGF2 (proliferating NSPCs) or FGF2+BMP4 (quiescent NSPCs) showing that entry into quiescence involves major changes in the transcriptional profile of the cells.
Project description:Postnatal neural stem cells are primarily quiescent, which is a cellular state that exists as a continuum from deep to shallow quiescence. The molecular changes that occur along this continuum are beginning to be understood but the transcription factor network governing these changes has not been defined. We show that these transitions are regulated by sequential transcription factor programs. Single-cell transcriptomic analyses of mice with loss- or gain-of-function of the essential activation factor Ascl1, reveal that Ascl1 promotes the activation of hippocampal neural stem cells by driving these cells out of deep quiescence, despite its low protein expression. Subsequently, during the transition from deep to shallow quiescence, Ascl1 induces the expression of Mycn, which drives progression through shallow states of quiescence towards an active state. Together, these results define the required sequence of transcription factors during hippocampal neural stem cell activation.
Project description:Neural stem cell numbers fall rapidly in the hippocampus of juvenile mice but stabilise during adulthood, ensuring lifelong hippocampal neurogenesis. We show that this reduction in stem cell depletion rate in young adults is the result of coordinated changes in stem cell behaviour. In particular, while proliferating neural stem cells in juveniles differentiate rapidly, they increasingly return to a resting state of shallow quiescence and progress through additional self-renewing divisions in adulthood. Single-cell transcriptomic, modelling and label-retention analyses indicate that resting cells have a higher activation rate and greater contribution to neurogenesis than dormant cells, which have not left quiescence. These progressive changes in stem cell behaviour result from reduced expression of the pro-activation protein ASCL1 due to increased post-translational degradation. These cellular mechanisms help reconcile current contradictory models of hippocampal NSC dynamics and may contribute to the different rates of decline of hippocampal neurogenesis in mammalian species including humans.
Project description:Experience governs neurogenesis from radial-glial neural stem cells (RGLs) in the adult hippocampus to support memory. Transcription factors in RGLs integrate physiological signals to dictate quiescence-activation decisions and self-renewal divisions. Whereas asymmetric RGL self-renewal drives neurogenesis during favorable conditions, symmetric divisions prevent premature neurogenesis during unfavorable conditions while amplifying RGLs to anticipate neurogenic demands when conditions become favorable. Here, we show that the transcription factor Kruppel-like factor 9 (Klf9) is enriched in quiescent RGLs and inducible, bidirectional modulation of Klf9 biases RGL quiescence-activation decisions. Clonal lineage tracing and longitudinal intravital two-photon imaging of RGLs following cell-autonomous Klf9 deletion directly demonstrated increased symmetric self-renewal. In vivo translational profiling of RGLs identified a Klf9-dependent blueprint for genetic and metabolic programs instructing RGL quiescence and expansion. Thus, experience dependent regulation of Klf9 in RGLs may ensure self-preservation of neural stem cells while anticipating future demands for neurogenesis and astrogenesis to support hippocampal functions.
Project description:Adult radial glia-like cells (RGLs) residing in the subgranular zone (SGZ) of the dentate gyrus (DG) are finely regulated to control the generation of new neurons. Quiescence is essential for the long-term maintenance of the RGL pool. Intrinsic factors as well as extrinsic niche signals orchestrate the balance between RGL quiescence and activation, but the mechanisms are still not completely understood. Yap1, a core factor of Hippo signaling, is very important for the proliferation of stem cells of various organs and species, such as intestinal stem cells of the mouse and neural stem cells in Drosophila brain. Here I addressed the role of Yap1 in adult hippocampal neurogenesis by gain- and loss-of-function studies. I found that the expression of Yap1 was enriched in adult RGLs, but was undetectable in other cell types such as neurons and cells of the oligodendroglial lineage. Through the analysis of conditional knock-out of Yap1 in adult RGLs and their lineage, I found that fewer RGLs became activated while a significantly higher proportion of RGLs remained in the quiescent state. Conversely, overexpression of constitutively active mutant variant of Yap1 (Yap1 5SA) induced the proliferation of quiescent RGLs in vitro and in vivo. This effect was dependent on functional interaction with the TEA Domain Transcription Factor (TEAD). Pharmacological blocking the interaction between endogenous Yap1 and TEAD by verteporfin reduced the rate of proliferation of neural progenitors in vitro, which indicates a physiological role of Yap1-TEAD interaction in regulating the transition between quiescence and activation. Interestingly, constitutive expression of Yap1 5SA in RGLs blocked adult neurogenesis and retained the cells in a progenitor-like (Sox2+) state. To further explore the molecular mechanisms of Yap1 in regulating the activation of quiescent RGLs, single-cell RNA sequencing analysis was performed at 3 and 7 days following Yap1 5SA overexpression. Yap1 5SA overexpressing cells exhibited increased signature of active NSCs but also displayed distinct features such as epithelial-to-mesenchymal transition (EMT). Importantly, we found that Catenin Beta 1 (CTNNB1) was upregulated suggesting a potential involvement of Wnt signaling in the proliferative effect of Yap1 5SA overexpression in adult NSCs. In sum, this work provides compelling evidence for regulation of the balance between activation and quiescence of adult hippocampal RGLs by Yap1.
Project description:We performed snRNA-seq of macaque hippocampal formation sample to investigate whether there is the existence of adult neural stem cells and adult hippocampal neurogenesis.