Stem cell fate can be influenced by metabolite levels in culture but it is unknown whether physiological variations in metabolite levels in normal tissues regulate stem cell function in vivo. We developed a metabolomics method for analysis of rare cell populations isolated directly from tissues and used it to compare haematopoietic stem cells (HSCs) to restricted haematopoietic progenitors. Each haematopoietic cell type had a distinct metabolic signature. Human and mouse HSCs had unusually high levels of ascorbate, which declined with differentiation. Systemic ascorbate depletion in mice increased HSC frequency and function, partly by reducing Tet2 function, a dioxygenase tumor suppressor. Ascorbate depletion cooperated with Flt3ITD leukaemic mutations to accelerate leukaemogenesis, though cell-autonomous and possibly non-cell-autonomous mechanisms, in a manner that was reversed by dietary ascorbate. Ascorbate acted cell-autonomously to negatively regulate HSC function and myelopoiesis through Tet2-dependent and Tet2-independent mechanisms. Ascorbate thus accumulates within HSCs to promote Tet function in vivo, limiting HSC frequency and suppressing leukaemogenesis.
Nucleosome assembly following DNA replication, DNA repair and gene transcription is critical for the maintenance of genome stability and epigenetic information. Nucleosomes are assembled via replication-coupled or replication-independent pathways with the aid of histone chaperone proteins. How these different nucleosome assembly pathways are regulated remains relatively unclear. Recent studies have provided insight into the mechanisms and the roles of histone chaperones regulating nucleosome assembly. Alterations or mutations in factors involved in nucleosome assembly have also been implicated in cancer and other human diseases. This review highlights the recent progress and outlines future challenges in the field.
Neurosphere formation is commonly used as a surrogate for neural stem cell (NSC) function but the relationship between neurosphere-initiating cells (NICs) and NSCs remains unclear. We prospectively identified, and isolated by flow cytometry, adult mouse lateral ventricle subventricular zone (SVZ) NICs as GlastmidEGFRhighPlexinB2highCD24−/lowO4/PSA-NCAM−/lowTer119/CD45− (GEPCOT) cells. They were highly mitotic and short-lived in vivo based on fate-mapping with Ascl1CreERT2 and Dlx1CreERT2. In contrast, pre-GEPCOT cells were quiescent, expressed higher Glast, and lower EGFR and PlexinB2. Pre-GEPCOT cells could not form neurospheres but expressed the stem cell markers Slc1a3-CreERT, GFAP-CreERT2, Sox2CreERT2, and Gli1CreERT2 and were long-lived in vivo. While GEPCOT NICs were ablated by temozolomide, pre-GEPCOT cells survived and repopulated the SVZ. Conditional deletion of the Bmi-1 polycomb protein depleted pre-GEPCOT and GEPCOT cells, though pre-GEPCOT cells were more dependent upon Bmi-1 for Cdkn2a (p16Ink4a) repression. Our data distinguish quiescent NSCs from NICs and make it possible to study their properties in vivo.DOI: http://dx.doi.org/10.7554/eLife.02669.001
Summary Acetylation of lysine residues at the H3 N-terminus is proposed to have a role in replication-coupled (RC) nucleosome assembly, a process critical for the inheritance of epigenetic information and maintenance of genome stability. However, the role of H3 N-terminal lysine acetylation and the corresponding lysine acetyltransferase (KAT) in RC nucleosome assembly are not known. Here we show that Gcn5, a KAT with a well-studied role in gene transcription, functions in parallel with Rtt109, the H3 lysine 56 KAT, to promote RC nucleosome assembly. Cells lacking both Gcn5 and Rtt109 are highly sensitive to DNA damaging agents. Moreover, cells lacking GCN5 or expressing an H3 mutant with mutations at the H3 N-terminus result in compromised deposition of new H3 onto replicating DNA and a reduction in the binding of H3 with CAF-1, a histone chaperone involved in RC nucleosome assembly. These results demonstrate that Gcn5 regulates RC nucleosome assembly, in part, through promoting the association of H3 with CAF-1 via H3 acetylation.
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