Project description:Across life neural stem cells (NSCs) generate new neurons in the mammalian brain through asymmetric neurogenic and self-renewing cell divisions. However, the cellular mechanisms underlying NSC asymmetry remain unknown. Using fluorescence loss in photobleaching (FLIP) we here show that NSCs in vitro and within the developing forebrain generate a lateral diffusion barrier during cell division resulting in asymmetric segregation of cellular components. The strength of the diffusion barrier is dynamically regulated with age and depends on the proper function of lamin-associated nuclear envelope constituents. Strikingly, age-associated or experimental impairment of the diffusion barrier disrupts asymmetric segregation of damaged proteins, a product of aging. Thus, the data presented here identify a mechanism how age is asymmetrically distributed during somatic stem cell division. For microarray analysis we analysed gene expression in cells derived from the hippocampi of 6 week old (young) or 9 month old (old) male C57BL/6JRj mice. 6 samples were analyzed YoungNSC, 3 replicates OldNSC, 3 replicates
Project description:Across life neural stem cells (NSCs) generate new neurons in the mammalian brain through asymmetric neurogenic and self-renewing cell divisions. However, the cellular mechanisms underlying NSC asymmetry remain unknown. Using fluorescence loss in photobleaching (FLIP) we here show that NSCs in vitro and within the developing forebrain generate a lateral diffusion barrier during cell division resulting in asymmetric segregation of cellular components. The strength of the diffusion barrier is dynamically regulated with age and depends on the proper function of lamin-associated nuclear envelope constituents. Strikingly, age-associated or experimental impairment of the diffusion barrier disrupts asymmetric segregation of damaged proteins, a product of aging. Thus, the data presented here identify a mechanism how age is asymmetrically distributed during somatic stem cell division.
Project description:Sivakumar2011 - Hedgehog Signaling Pathway
This is the current model for the Hedgehog signaling pathway. The best data for mechanism of signaling has been worked out in Drosophila, so this model is based largely on Drosophila data. Hedgehog target genes vary from tissue to tissue, so the identities of individual target genes have not been listed. The main difference between the Drosophila and mammalian Hedgehog signaling pathways is the fact that there are three mammalian homologs of Cubitus interruptus, Gli1 Gli2 and Gli3. Some or all of the mammalian homologs may be proteolytically processed, but the data are controversial. There are two mammalian Ptc genes and three mammalian Hedgehog genes as well. The pathway for Sonic Hedgehog appears to be most similar to the Drosophila hedgehog pathway.
References:
Hedgehog signaling in animal development: paradigms and principles.
Sonic hedgehog in the nervous system: functions, modifications and mechanisms.
Hedgehog signal transduction: recent findings.
Hedgehog signaling: Costal-2 bridges the transduction gap.
This model is described in the article:
A systems biology approach to model neural stem cell regulation by notch, shh, wnt, and EGF signaling pathways.
Sivakumar KC, Dhanesh SB, Shobana S, James J, Mundayoor S.
Omics: a Journal of Integrative Biology. 2011; 15(10):729-737
Abstract:
The Notch, Sonic Hedgehog (Shh), Wnt, and EGF pathways have long been known to influence cell fate specification in the developing nervous system. Here we attempted to evaluate the contemporary knowledge about neural stem cell differentiation promoted by various drug-based regulations through a systems biology approach. Our model showed the phenomenon of DAPT-mediated antagonism of Enhancer of split [E(spl)] genes and enhancement of Shh target genes by a SAG agonist that were effectively demonstrated computationally and were consistent with experimental studies. However, in the case of model simulation of Wnt and EGF pathways, the model network did not supply any concurrent results with experimental data despite the fact that drugs were added at the appropriate positions. This paves insight into the potential of crosstalks between pathways considered in our study. Therefore, we manually developed a map of signaling crosstalk, which included the species connected by representatives from Notch, Shh, Wnt, and EGF pathways and highlighted the regulation of a single target gene, Hes-1, based on drug-induced simulations. These simulations provided results that matched with experimental studies. Therefore, these signaling crosstalk models complement as a tool toward the discovery of novel regulatory processes involved in neural stem cell maintenance, proliferation, and differentiation during mammalian central nervous system development. To our knowledge, this is the first report of a simple crosstalk map that highlights the differential regulation of neural stem cell differentiation and underscores the flow of positive and negative regulatory signals modulated by drugs.
This model is hosted on BioModels Database and identified by: BIOMD0000000395.
To cite BioModels Database, please use: BioModels Database: An enhanced, curated and annotated resource for published quantitative kinetic models.
To the extent possible under law, all copyright and related or neighbouring rights to this encoded model have been dedicated to the public domain worldwide. Please refer to CC0 Public Domain Dedication for more information.
Project description:Neural stem cells (NSCs) generate neurons throughout life in the hippocampal dentate gyrus (DG). With advancing age levels of neurogenesis sharply drop, which has been associated with a decline in hippocampal memory function. However, cell-intrinsic mechanisms mediating age-related changes in NSC activity remain largely unknown. Here we show that the nuclear lamina protein Lamin B1 (LB1) is downregulated with age in mouse hippocampal NSCs. LB1 is cross-regulated with Sun-domain containing protein 1 (SUN1), previously implicated in Hutchinson-Gilford progeria syndrome (HGPS), a disease of premature aging. LB1 and SUN1 govern the strength of a diffusion barrier in the membrane of the endoplasmic reticulum (ER) that is associated with the segregation of aging factors during NSC divisions. Balancing the levels of LB1 and SUN1 in aged NSCs restores the ER-diffusion barrier. Virus-based restoration of LB1 expression in aged NSCs enhances stem cell activity in vitro and increases progenitor cell proliferation and neurogenesis in vivo. Thus, we here identify a novel mechanism associated with the age-related decline of neurogenesis in the mammalian hippocampus.
Project description:Endogenous neural stem cells reside in the mammalian brain during development and within special niche microenvironments during adulthood. We discovered that endothelial progenitor cell-secreted factors promote the self-renewal of adult mouse NSCs in vivo and identified this protein as ECF-L. We also analyzed molecular signalling networks caused by ECF-L in neural stem cells using global gene expression analysis. Neural stem cells were isolated and expanded from adult mouse brain. Neural stem cells were cultured in the presence or absence of ECF-L in the MHM medium. After the designed period of ECF-L treatment, cells were harvested and RNA was extacted, followed by DNA microarray analysis.
Project description:Neural stem/progenitor cell (NSPC) proliferation and self-renewal, as well as insult-induced differentiation, decrease markedly with age, but the molecular mechanisms responsible for these declines remain unclear. Here we show that levels of NAD+ and nicotinamide phosphoribosyltransferase (Nampt), the rate-limiting enzyme in mammalian NAD+ biosynthesis, decrease with age in the hippocampus. Ablation of Nampt in adult NSPCs reduced their pool and proliferation in vivo. The decrease in the NSPC pool during aging can be rescued by enhancing hippocampal NAD+ levels. Nampt is the main source of NSPC NAD+ levels and required for G1/S progression of the NSPC cell cycle. Nampt is also critical for oligodendrocytic lineage fate decisions through a mechanism mediated redundantly by Sirt1 and Sirt2. Ablation of Nampt in the adult NSPCs in vivo reduced NSPC-mediated oligodendrogenesis upon injury. These phenotypes recapitulate defects in NSPCs during aging, implicating Nampt-mediated NAD+ biosynthesis as a mediator of these age-associated functional declines. Total RNA obtained from neurospheres derived from postnatal hippocampi subjected to 48 hours in vitro of incubation with Nampt-specific inhibitor FK866 (10 nM, 4 samples) or vehicle (DMSO, 1:1000, 4 samples).
Project description:Neural stem cells (NSCs) in the adult mammalian subependymal zone maintain a glial identity and the developmental potential to generate neurons during the lifetime. Production of neurons from these NSCs is not direct but follows an orderly pattern of cell progression which allows the gradual increase along the neurogenic lineage in the expression of pro-neural factors needed for neuronal specification. In this context, tightly regulated translation of existing transcriptional programs represents a potential mechanism to avoid the critical challenge posed by genes that encode proteins with conflicting functions, i.e. self-renew or differentiate. Here, we identify RNA-binding protein MEX3A as a post-transcriptional regulator of a set of stemness-associated transcripts at critical transitions in the subependymal neurogenic lineage. MEX3A binding to a set of quiescence-related RNAs in activated NSCs is needed for their return to quiescence, playing a role in the long-term maintenance of the NSC pool. Furthermore, it is required for the repression of the same program at the onset of neuronal differentiation. Our data indicate that MEX3A is a pivotal regulator of adult mammalian neurogenesis acting as a translational remodeller.
Project description:Suppressing spurious cryptic transcription by a repressive intragenic chromatin state featuring trimethylated lysine 36 on histone H3 (H3K36me3) and DNA methylation is critical for maintaining self-renewal capacity in mouse embryonic stem cells. In yeast and nematodes, such cryptic transcription is elevated with age, and reducing the levels of age-associated cryptic transcription extends yeast lifespan. Whether cryptic transcription is also increased during mammalian aging is unknown. We show for the first time an age-associated elevation in cryptic transcription in several stem cell populations, including murine hematopoietic stem cells (mHSCs) and neuronal stem cells (NSCs) and human mesenchymal stem cells (hMSCs). Using DECAP-seq, we mapped and quantified age-associated cryptic transcription in hMSCs aged in vitro. Regions with significant age-associated cryptic transcription have a unique chromatin signature: decreased H3K36me3 and increased H3K4me1, H3K4me3, and H3K27ac with age. Furthermore, genomic regions undergoing such age-dependent chromatin changes resemble known promoter sequences and are bound by the promoter-associated protein TBP even in young cells. Hence, the more permissive chromatin state at intragenic cryptic promoters likely underlies the increase of cryptic transcription in aged mammalian stem cells.
Project description:Suppressing spurious cryptic transcription by a repressive intragenic chromatin state featuring trimethylated lysine 36 on histone H3 (H3K36me3) and DNA methylation is critical for maintaining self-renewal capacity in mouse embryonic stem cells. In yeast and nematodes, such cryptic transcription is elevated with age, and reducing the levels of age-associated cryptic transcription extends yeast lifespan. Whether cryptic transcription is also increased during mammalian aging is unknown. We show for the first time an age-associated elevation in cryptic transcription in several stem cell populations, including murine hematopoietic stem cells (mHSCs) and neuronal stem cells (NSCs) and human mesenchymal stem cells (hMSCs). Using DECAP-seq, we mapped and quantified age-associated cryptic transcription in hMSCs aged in vitro. Regions with significant age-associated cryptic transcription have a unique chromatin signature: decreased H3K36me3 and increased H3K4me1, H3K4me3, and H3K27ac with age. Furthermore, genomic regions undergoing such age-dependent chromatin changes resemble known promoter sequences and are bound by the promoter-associated protein TBP even in young cells. Hence, the more permissive chromatin state at intragenic cryptic promoters likely underlies the increase of cryptic transcription in aged mammalian stem cells.