Growing evidence suggests that the lysine methyltransferase DOT1L/KMT4 has important roles in proliferation, survival, and differentiation of stem cells in development and in disease. We investigated the function of DOT1L in neural stem cells (NSCs) of the cerebral cortex. The pharmacological inhibition and shRNA-mediated knockdown of DOT1L impaired proliferation and survival of NSCs. DOT1L inhibition specifically induced genes that are activated during the unfolded protein response (UPR) in the endoplasmic reticulum (ER). Chromatin-immunoprecipitation analyses revealed that two genes encoding for central molecules involved in the ER stress response, Atf4 and Ddit3 (Chop), are marked with H3K79 methylation. Interference with DOT1L activity resulted in transcriptional activation of both genes accompanied by decreased levels of H3K79 dimethylation. Although downstream effectors of the UPR, such as Ppp1r15a/Gadd34, Atf3, and Tnfrsf10b/ Dr5 were also transcriptionally activated, this most likely occurred in response to increased ATF4 expression rather than as a direct consequence of altered H3K79 methylation. While stem cells are particularly vulnerable to stress, the UPR and ER stress have not been extensively studied in these cells yet. Since activation of the ER stress program is also implicated in directing stem cells into differentiation or to maintain a proliferative status, the UPR must be tightly regulated. Our and published data suggest that histone modifications, including H3K4me3, H3K14ac, and H3K79me2, are implicated in the control of transcriptional activation of ER stress genes. In this context, the loss of H3K79me2 at the Atf4-and Ddit3-promoters appears to mark a point-of-no-return that activates the death program in NSCs. STEM CELLS 2016;34:233-245 SIGNIFICANCE STATEMENTPosttranslational histone modification control gene expression. They are means to pass on transcriptional information from one cell generation to another. We describe the impact of histone H3 dimethylation at lysine 79 (H3K79me2) in neural stem cells. Inhibiting the enzymatic activity mediating this modification leads to cell division defects and cell death by controlling expression of central transcription factors implicated in stress response. Histone methylations are a way to balance how stem cells can cope with the activation of the stress response, which can range from proliferation to differentiation and, in case of H3K79me2, to the control of cell death.

Simultaneous generation of neural cells and that of the nutrient-supplying vasculature during brain development is called neurovascular coupling. We report on a transgenic mouse with impaired transforming growth factor β (TGFβ)-signalling in forebrain-derived neural cells using a Foxg1-cre knock-in to drive the conditional knock-out of the Tgfbr2. Although the expression of FOXG1 is assigned to neural progenitors and neurons of the telencephalon, Foxg1cre/+;Tgfbr2flox/flox (Tgfbr2-cKO) mutants displayed intracerebral haemorrhage. Blood vessels exhibited an atypical, clustered appearance were less in number and displayed reduced branching. Vascular endothelial growth factor (VEGF) A, insulin-like growth factor (IGF) 1, IGF2, TGFβ, inhibitor of DNA binding (ID) 1, thrombospondin (THBS) 2, and a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS) 1 were altered in either expression levels or tissue distribution. Accordingly, human umbilical vein endothelial cells (HUVEC) displayed branching defects after stimulation with conditioned medium (CM) that was derived from primary neural cultures of the ventral and dorsal telencephalon of Tgfbr2-cKO. Supplementing CM of Tgfbr2-cKO with VEGFA rescued these defects, but application of TGFβ aggravated them. HUVEC showed reduced migration towards CM of mutants compared with controls. Supplementing the CM with growth factors VEGFA, fibroblast growth factor (FGF) 2 and IGF1 partially restored HUVEC migration. In contrast, TGFβ supplementation further impaired migration of HUVEC. We observed differences along the dorso-ventral axis of the telencephalon with regard to the impact of these factors on the phenotype. Together these data establish a TGFBR2-dependent molecular crosstalk between neural and endothelial cells during brain vessel development. These findings will be useful to further elucidate neurovascular interaction in general and to understand pathologies of the blood vessel system such as intracerebral haemorrhages, hereditary haemorrhagic telangiectasia, Alzheimeŕs disease, cerebral amyloid angiopathy or tumour biology.

Post-translational modification of histone proteins, such as the methylation of lysine and arginine residues, influences the higher order of chromatin and leads to gene activation or silencing. Histone methyltransferases or demethylases actively add or remove various methylation marks in a cell-type-specific and context-dependent way. They are therefore important players in regulating the transcriptional program of a cell. Some control of the various cellular programs is necessary during the differentiation of stem cells along a specific lineage, when differentiation to alternative lineages needs to be suppressed. One example is the development of neurons from neural stem cells during neurogenesis. Neurogenesis is a highly organized process that requires the proper coordination of survival, proliferation, differentiation and migration signals. This holds true for both embryonic and neural stem cells that give rise to the various cell types of the central nervous system. The control of embryonic and neural stem cell self-renewal and differentiation is achieved by both extrinsic and intrinsic signals that regulate gene expression precisely. Recent advances in neuroscience support the importance of epigenetic modifications, such as the methylation and acetylation of histones, as an important intrinsic mechanism for the regulation of central nervous system development. This review summarizes our current knowledge of histone methylation processes during neural development and provides insights into the function of histone methylation enzymes and their role during central nervous system development.

Brain development is a complex process, which is controlled in a temporo-spatial manner by gradients of morphogens and different transcriptional programs. Additionally, epigenetic chromatin modifications, like histone methylation, have an important role for establishing and maintaining specific cell fates within this process. The vast majority of histone methylation occurs on the flexible histone tail, which is accessible to histone modifiers, erasers, and histone reader proteins. In contrast, H3K79 methylation is located in the globular domain of histone 3 and is implicated in different developmental functions. H3K79 methylation is evolutionarily conserved and can be found in a wide range of species from Homo sapiens to Saccharomyces cerevisiae. The modification occurs in different cell populations within organisms, including neural progenitors. The location of H3K79 methylation in the globular domain of histone 3 makes it difficult to assess. Here, we present methods to isolate and culture cortical progenitor cells (CPCs) from embryonic cortical brain tissue (E11.5-E14.5) or cerebellar granular neuron progenitors (CGNPs) from postnatal tissue (P5-P7), and to efficiently immunoprecipitate H3K79me2 for quantitative PCR (qPCR) and genome-wide sequencing.

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