Early fate bias in neuroepithelial progenitors of hippocampal neurogenesis.

Hippocampal adult neural stem cells emerge from progeny of the neuroepithelial lineage during murine brain development. Hippocampus development is increasingly well understood. However, the clonal relationships between early neuroepithelial stem cells and postnatal neurogenic cells remain unclear, especially at the single-cell level. Here we report fate bias and gene expression programs in thousands of clonally related cells in the juvenile hippocampus based on single-cell RNA-seq of barcoded clones. We find evidence for early fate restriction of neuroepithelial stem cells to either neurogenic progenitor cells of the dentate gyrus region or oligodendrogenic, non-neurogenic fate supplying cells for other hippocampal regions including gray matter areas and the Cornu ammonis region 1/3. Our study provides new insights into the phenomenon of early fate restriction guiding the development of postnatal hippocampal neurogenesis.

Acute sleep loss alters circulating fibroblast growth factor 21 levels in humans: A randomised crossover trial.

The hormone fibroblast growth factor 21 (FGF21) modulates tissue metabolism and circulates at higher levels in metabolic conditions associated with chronic sleep-wake disruption, such as type 2 diabetes and obesity. In the present study, we investigated whether acute sleep loss impacts circulating levels of FGF21 and tissue-specific production, and response pathways linked to FGF21. A total of 15 healthy normal-weight young men participated in a randomised crossover study with two conditions, sleep loss versus an 8.5-hr sleep window. The evening before each intervention, fasting blood was collected. Fasting, post-intervention morning skeletal muscle and adipose tissue samples underwent quantitative polymerase chain reaction and DNA methylation analyses, and serum FGF21 levels were measured before and after an oral glucose tolerance test. Serum levels of FGF21 were higher after sleep loss compared with sleep, both under fasting conditions and following glucose intake (~27%-30%, p = 0.023). Fasting circulating levels of fibroblast activation protein, a protein which can degrade circulating FGF21, were not altered by sleep loss, whereas DNA methylation in the FGF21 promoter region increased only in adipose tissue. However, even though specifically the muscle exhibited transcriptional changes indicating adverse alterations to redox and metabolic homeostasis, no tissue-based changes were observed in expression of FGF21, its receptors, or selected signalling targets, in response to sleep loss. In summary, we found that acute sleep loss resulted in increased circulating levels of FGF21 in healthy young men, which may occur independent of a tissue-based stress response in metabolic peripheral tissues. Further studies may decipher whether changes in FGF21 signalling after sleep loss modulate metabolic outcomes associated with sleep or circadian disruption.

Neurophysiological defects and neuronal gene deregulation in Drosophila mir-124 mutants.

miR-124 is conserved in sequence and neuronal expression across the animal kingdom and is predicted to have hundreds of mRNA targets. Diverse defects in neural development and function were reported from miR-124 antisense studies in vertebrates, but a nematode knockout of mir-124 surprisingly lacked detectable phenotypes. To provide genetic insight from Drosophila, we deleted its single mir-124 locus and found that it is dispensable for gross aspects of neural specification and differentiation. On the other hand, we detected a variety of mutant phenotypes that were rescuable by a mir-124 genomic transgene, including short lifespan, increased dendrite variation, impaired larval locomotion, and aberrant synaptic release at the NMJ. These phenotypes reflect extensive requirements of miR-124 even under optimal culture conditions. Comparison of the transcriptomes of cells from wild-type and mir-124 mutant animals, purified on the basis of mir-124 promoter activity, revealed broad upregulation of direct miR-124 targets. However, in contrast to the proposed mutual exclusion model for miR-124 function, its functional targets were relatively highly expressed in miR-124-expressing cells and were not enriched in genes annotated with epidermal expression. A notable aspect of the direct miR-124 network was coordinate targeting of five positive components in the retrograde BMP signaling pathway, whose activation in neurons increases synaptic release at the NMJ, similar to mir-124 mutants. Derepression of the direct miR-124 target network also had many secondary effects, including over-activity of other post-transcriptional repressors and a net incomplete transition from a neuroblast to a neuronal gene expression signature. Altogether, these studies demonstrate complex consequences of miR-124 loss on neural gene expression and neurophysiology.

Histone modifications influence mediator interactions with chromatin.

The Mediator complex transmits activation signals from DNA bound transcription factors to the core transcription machinery. Genome wide localization studies have demonstrated that Mediator occupancy not only correlates with high levels of transcription, but that the complex also is present at transcriptionally silenced locations. We provide evidence that Mediator localization is guided by an interaction with histone tails, and that this interaction is regulated by their post-translational modifications. A quantitative, high-density genetic interaction map revealed links between Mediator components and factors affecting chromatin structure, especially histone deacetylases. Peptide binding assays demonstrated that pure wild-type Mediator forms stable complexes with the tails of Histone H3 and H4. These binding assays also showed Mediator-histone H4 peptide interactions are specifically inhibited by acetylation of the histone H4 lysine 16, a residue critical in transcriptional silencing. Finally, these findings were validated by tiling array analysis that revealed a broad correlation between Mediator and nucleosome occupancy in vivo, but a negative correlation between Mediator and nucleosomes acetylated at histone H4 lysine 16. Our studies show that chromatin structure and the acetylation state of histones are intimately connected to Mediator localization.

Clonal relations in the mouse brain revealed by single-cell and spatial transcriptomics.

The mammalian brain contains many specialized cells that develop from a thin sheet of neuroepithelial progenitor cells. Single-cell transcriptomics revealed hundreds of molecularly diverse cell types in the nervous system, but the lineage relationships between mature cell types and progenitor cells are not well understood. Here we show in vivo barcoding of early progenitors to simultaneously profile cell phenotypes and clonal relations in the mouse brain using single-cell and spatial transcriptomics. By reconstructing thousands of clones, we discovered fate-restricted progenitor cells in the mouse hippocampal neuroepithelium and show that microglia are derived from few primitive myeloid precursors that massively expand to generate widely dispersed progeny. We combined spatial transcriptomics with clonal barcoding and disentangled migration patterns of clonally related cells in densely labeled tissue sections. Our approach enables high-throughput dense reconstruction of cell phenotypes and clonal relations at the single-cell and tissue level in individual animals and provides an integrated approach for understanding tissue architecture.

Characterization of the nuclear and cytosolic transcriptomes in human brain tissue reveals new insights into the subcellular distribution of RNA transcripts.

Transcriptome analysis has mainly relied on analyzing RNA sequencing data from whole cells, overlooking the impact of subcellular RNA localization and its influence on our understanding of gene function, and interpretation of gene expression signatures in cells. Here, we separated cytosolic and nuclear RNA from human fetal and adult brain samples and performed a comprehensive analysis of cytosolic and nuclear transcriptomes. There are significant differences in RNA expression for protein-coding and lncRNA genes between cytosol and nucleus. We show that transcripts encoding the nuclear-encoded mitochondrial proteins are significantly enriched in the cytosol compared to the rest of protein-coding genes. Differential expression analysis between fetal and adult frontal cortex show that results obtained from the cytosolic RNA differ from results using nuclear RNA both at the level of transcript types and the number of differentially expressed genes. Our data provide a resource for the subcellular localization of thousands of RNA transcripts in the human brain and highlight differences in using the cytosolic or the nuclear transcriptomes for expression analysis.

Transcriptional profiling reveals a critical role for tyrosine phosphatase VE-PTP in regulation of VEGFR2 activity and endothelial cell morphogenesis.

To define molecular events accompanying formation of the 3-dimensional (3D) vascular tube, we have characterized gene expression during vascular endothelial growth factor (VEGF)-induced tubular morphogenesis of endothelial cells. Microarray analyses were performed comparing gene induction in growth-arrested, tube-forming endothelial cells harvested from 3D collagen cultures to that in proliferating endothelial cells cultured on fibronectin. Differentially expressed genes were clustered and analyzed for specific endothelial expression through publicly available datasets. We validated the contribution of one of the identified genes, vascular endothelial protein tyrosine phosphatase (VE-PTP), to endothelial morphogenesis. Silencing of VE-PTP expression was accompanied by increased VEGF receptor-2 (VEGFR2) tyrosine phosphorylation and activation of downstream signaling pathways. The increased VEGFR2 activity promoted endothelial cell cycle progression, overcoming the G(0)/G(1) arrest associated with organization into tubular structures in the 3D cultures. Proximity ligation showed close association between VEGFR2 and VE-PTP in resting cells. Activation of VEGFR2 by VEGF led to rapid loss of association, which was resumed with time in parallel with decreased receptor activity. In conclusion, we have identified genes, which may serve critical functions in formation of the vascular tube. One of these, VE-PTP, regulates VEGFR2 activity thereby modulating the VEGF-response during angiogenesis.

Genome-scale study of the importance of binding site context for transcription factor binding and gene regulation.

BACKGROUND: The rate of mRNA transcription is controlled by transcription factors that bind to specific DNA motifs in promoter regions upstream of protein coding genes. Recent results indicate that not only the presence of a motif but also motif context (for example the orientation of a motif or its location relative to the coding sequence) is important for gene regulation. RESULTS: In this study we present ContextFinder, a tool that is specifically aimed at identifying cases where motif context is likely to affect gene regulation. We used ContextFinder to examine the role of motif context in S. cerevisiae both for DNA binding by transcription factors and for effects on gene expression. For DNA binding we found significant patterns of motif location bias, whereas motif orientations did not seem to matter. Motif context appears to affect gene expression even more than it affects DNA binding, as biases in both motif location and orientation were more frequent in promoters of co-expressed genes. We validated our results against data on nucleosome positioning, and found a negative correlation between preferred motif locations and nucleosome occupancy. CONCLUSION: We conclude that the requirement for stable binding of transcription factors to DNA and their subsequent function in gene regulation can impose constraints on motif context.

Combinatorial control of gene expression by the three yeast repressors Mig1, Mig2 and Mig3.

BACKGROUND: Expression of a large number of yeast genes is repressed by glucose. The zinc finger protein Mig1 is the main effector in glucose repression, but yeast also has two related proteins: Mig2 and Mig3. We have used microarrays to study global gene expression in all possible combinations of mig1, mig2 and mig3 deletion mutants. RESULTS: Mig1 and Mig2 repress a largely overlapping set of genes on 2% glucose. Genes that are upregulated in a mig1 mig2 double mutant were grouped according to the contribution of Mig2. Most of them show partially redundant repression, with Mig1 being the major repressor, but some genes show complete redundancy, and some are repressed only by Mig1. Several redundantly repressed genes are involved in phosphate metabolism. The promoters of these genes are enriched for Pho4 sites, a novel GGGAGG motif, and a variant Mig1 site which is absent from genes repressed only by Mig1. Genes repressed only by Mig1 on 2% glucose include the hexose transporter gene HXT4, but Mig2 contributes to HXT4 repression on 10% glucose. HXT6 is one of the few genes that are more strongly repressed by Mig2. Mig3 does not seem to overlap in function with Mig1 and Mig2. Instead, Mig3 downregulates the SIR2 gene encoding a histone deacetylase involved in gene silencing and the control of aging. CONCLUSION: Mig2 fine-tunes glucose repression by targeting a subset of the Mig1-repressed genes, and by responding to higher glucose concentrations. Mig3 does not target the same genes as Mig1 and Mig2, but instead downregulates the SIR2 gene.

Expression profiling and in situ screening of circular RNAs in human tissues.

Circular RNAs (circRNAs) were recently discovered as a class of widely expressed noncoding RNA and have been implicated in regulation of gene expression. However, the function of the majority of circRNAs remains unknown. Studies of circRNAs have been hampered by a lack of essential approaches for detection, quantification and visualization. We therefore developed a target-enrichment sequencing method suitable for screening of circRNAs and their linear counterparts in large number of samples. We also applied padlock probes and in situ sequencing to visualize and determine circRNA localization in human brain tissue at subcellular levels. We measured circRNA abundance across different human samples and tissues. Our results highlight the potential of this RNA class to act as a specific diagnostic marker in blood and serum, by detection of circRNAs from genes exclusively expressed in the brain. The powerful and scalable tools we present will enable studies of circRNA function and facilitate screening of circRNA as diagnostic biomarkers.

Acute sleep loss results in tissue-specific alterations in genome-wide DNA methylation state and metabolic fuel utilization in humans.

Curtailed sleep promotes weight gain and loss of lean mass in humans, although the underlying molecular mechanisms are poorly understood. We investigated the genomic and physiological impact of acute sleep loss in peripheral tissues by obtaining adipose tissue and skeletal muscle after one night of sleep loss and after one full night of sleep. We find that acute sleep loss alters genome-wide DNA methylation in adipose tissue, and unbiased transcriptome-, protein-, and metabolite-level analyses also reveal highly tissue-specific changes that are partially reflected by altered metabolite levels in blood. We observe transcriptomic signatures of inflammation in both tissues following acute sleep loss, but changes involving the circadian clock are evident only in skeletal muscle, and we uncover molecular signatures suggestive of muscle breakdown that contrast with an anabolic adipose tissue signature. Our findings provide insight into how disruption of sleep and circadian rhythms may promote weight gain and sarcopenia.

Heterogeneity and interplay of the extracellular vesicle small RNA transcriptome and proteome.

Extracellular vesicles (EVs) mediate cell-to-cell communication by delivering or displaying macromolecules to their recipient cells. While certain broad-spectrum EV effects reflect their protein cargo composition, others have been attributed to individual EV-loaded molecules such as specific miRNAs. In this work, we have investigated the contents of vesicular cargo using small RNA sequencing of cells and EVs from HEK293T, RD4, C2C12, Neuro2a and C17.2. The majority of RNA content in EVs (49-96%) corresponded to rRNA-, coding- and tRNA fragments, corroborating with our proteomic analysis of HEK293T and C2C12 EVs which showed an enrichment of ribosome and translation-related proteins. On the other hand, the overall proportion of vesicular small RNA was relatively low and variable (2-39%) and mostly comprised of miRNAs and sequences mapping to piRNA loci. Importantly, this is one of the few studies, which systematically links vesicular RNA and protein cargo of vesicles. Our data is particularly useful for future work in unravelling the biological mechanisms underlying vesicular RNA and protein sorting and serves as an important guide in developing EVs as carriers for RNA therapeutics.

Massive and parallel expression profiling using microarrayed single-cell sequencing.

Single-cell transcriptome analysis overcomes problems inherently associated with averaging gene expression measurements in bulk analysis. However, single-cell analysis is currently challenging in terms of cost, throughput and robustness. Here, we present a method enabling massive microarray-based barcoding of expression patterns in single cells, termed MASC-seq. This technology enables both imaging and high-throughput single-cell analysis, characterizing thousands of single-cell transcriptomes per day at a low cost (0.13 USD/cell), which is two orders of magnitude less than commercially available systems. Our novel approach provides data in a rapid and simple way. Therefore, MASC-seq has the potential to accelerate the study of subtle clonal dynamics and help provide critical insights into disease development and other biological processes.

Endocan is a VEGF-A and PI3K regulated gene with increased expression in human renal cancer.

An in vitro model of VEGF-A-induced angiogenesis was used to generate transcription profiles of human microvascular endothelial cells. Microarray analysis showed increased transcription of genes known to regulate angiogenesis, but also genes that previously have not been firmly associated with angiogenesis such as endocan, pinin, plakophilin, phosphodiesterase 4B and gelsolin. Increased endocan mRNA levels in response to VEGF-A in endothelial cells and in human renal cancer have previously been reported. We now show increased endocan protein levels in VEGF-A treated endothelial cells and in human renal clear cell carcinoma. Increased protein expression was observed both in tumor cells and in a subset of tumor vessels, while expression in normal kidney tissue was low. VEGF-A seemed to be a specific inducer of endocan transcription since FGF-2, PDGF-BB, HGF/SF and EGF did not alter expression levels. Inhibition of PI3K with LY294002 caused a 12-fold increase in endocan transcription suggesting a repressive function of PI3K. In contrast inhibition of Src or MEK, which are signaling pathways activated by VEGF-A, did not influence basal or VEGF-A-induced endocan levels. In conclusion our study shows that, among angiogenic growth factors, VEGF-A is a specific inducer of endocan transcription which is translated into increased protein levels in VEGF-A treated endothelial cells. Increased endocan protein expression in human renal cancer suggests a role in tumor growth.

Global gene expression analysis by combinatorial optimization.

Generally, there is a trade-off between methods of gene expression analysis that are precise but labor-intensive, e.g. RT-PCR, and methods that scale up to global coverage but are not quite as quantitative, e.g. microarrays. In the present paper, we show how how a known method of gene expression profiling (K. Kato, Nucleic Acids Res. 23, 3685-3690 (1995)), which relies on a fairly small number of steps, can be turned into a global gene expression measurement by advanced data post-processing, with potentially little loss of accuracy. Post-processing here entails solving an ancillary combinatorial optimization problem. Validation is performed on in silico experiments generated from the FANTOM data base of full-length mouse cDNA. We present two variants of the method. One uses state-of-the-art commercial software for solving problems of this kind, the other a code developed by us specifically for this purpose, released in the public domain under GPL license.