Martin Vickers

DNA demethylation is initiated in the central cells of Arabidopsis and rice

Significance Flowering plant reproduction involves two fertilization events: a sperm–egg fusion that forms the embryo, and a sperm–central cell fusion that forms the nutritive extraembryonic endosperm. Chromosomes in the embryo, endosperm, and other plant tissues are modified by methylation, a covalent addition to cytosine in DNA that regulates gene expression. Maternal endosperm chromosomes inherited from the central cell display a pattern of extensive demethylation, which is essential for seed development in Arabidopsis thaliana. Demethylation is presumed to occur in the central cell, but direct evidence for this is very limited. Here, we provide a genome-wide DNA methylation analysis of Arabidopsis and rice central cells, which demonstrates that the demethylation observed in the endosperm is indeed initiated in the central cell. Cytosine methylation is a DNA modification with important regulatory functions in eukaryotes. In flowering plants, sexual reproduction is accompanied by extensive DNA demethylation, which is required for proper gene expression in the endosperm, a nutritive extraembryonic seed tissue. Endosperm arises from a fusion of a sperm cell carried in the pollen and a female central cell. Endosperm DNA demethylation is observed specifically on the chromosomes inherited from the central cell in Arabidopsis thaliana, rice, and maize, and requires the DEMETER DNA demethylase in Arabidopsis. DEMETER is expressed in the central cell before fertilization, suggesting that endosperm demethylation patterns are inherited from the central cell. Down-regulation of the MET1 DNA methyltransferase has also been proposed to contribute to central cell demethylation. However, with the exception of three maize genes, central cell DNA methylation has not been directly measured, leaving the origin and mechanism of endosperm demethylation uncertain. Here, we report genome-wide analysis of DNA methylation in the central cells of Arabidopsis and rice—species that diverged 150 million years ago—as well as in rice egg cells. We find that DNA demethylation in both species is initiated in central cells, which requires DEMETER in Arabidopsis. However, we do not observe a global reduction of CG methylation that would be indicative of lowered MET1 activity; on the contrary, CG methylation efficiency is elevated in female gametes compared with nonsexual tissues. Our results demonstrate that locus-specific, active DNA demethylation in the central cell is the origin of maternal chromosome hypomethylation in the endosperm.

Sexual-lineage-specific DNA methylation regulates meiosis in Arabidopsis

DNA methylation regulates eukaryotic gene expression and is extensively reprogrammed during animal development. However, whether developmental methylation reprogramming during the sporophytic life cycle of flowering plants regulates genes is presently unknown. Here we report a distinctive gene-targeted RNA-directed DNA methylation (RdDM) activity in the Arabidopsis thaliana male sexual lineage that regulates gene expression in meiocytes. Loss of sexual-lineage-specific RdDM causes mis-splicing of the MPS1 gene (also known as PRD2), thereby disrupting meiosis. Our results establish a regulatory paradigm in which de novo methylation creates a cell-lineage-specific epigenetic signature that controls gene expression and contributes to cellular function in flowering plants.RNA-directed DNA methylation (RdDM) in the Arabidopsis thaliana male sexual lineage is shown here to regulate gene expression in meiocytes. Loss of sexual-lineage-specific RdDM causes mis-splicing of the MPS1 gene, thereby disrupting meiosis

The anti-fecundity effect of 5-azacytidine (5-AzaC) on Schistosoma mansoni is linked to dis-regulated transcription, translation and stem cell activities.

Uncontrolled host immunological reactions directed against tissue-trapped eggs precipitate a potentially lethal, pathological cascade responsible for schistosomiasis. Blocking schistosome egg production, therefore, presents a strategy for simultaneously reducing immunopathology as well as limiting disease transmission in endemic or emerging areas. We recently demonstrated that the ribonucleoside analogue 5-azacytidine (5-AzaC) inhibited Schistosoma mansoni oviposition, egg maturation and ovarian development. While these anti-fecundity effects were associated with a loss of DNA methylation, other molecular processes affected by 5-AzaC were not examined at the time. By comparing the transcriptomes of 5-AzaC-treated females to controls, we provide evidence that this ribonucleoside analogue also modulates other crucial aspects of schistosome egg-laying biology. For example, S. mansoni gene products associated with amino acid-, carbohydrate-, fatty acid-, nucleotide- and tricarboxylic acid (TCA)- homeostasis are all dysregulated in 5-AzaC treated females. To validate the metabolic pathway most significantly affected by 5-AzaC, amino acid metabolism, nascent protein synthesis was subsequently quantified in adult schistosomes. Here, 5-AzaC inhibited this process by 68% ±16.7% (SEM) in male- and 81% ±4.8% (SEM) in female-schistosomes. Furthermore, the transcriptome data indicated that adult female stem cells were also affected by 5-AzaC. For instance, 40% of transcripts associated with proliferating schistosome cells were significantly down-regulated by 5-AzaC. This finding correlated with a considerable reduction (95%) in the number of 5-ethynyl-2′-deoxyuridine (EdU) positive cells found in 5-AzaC-treated females. In addition to protein coding genes, the effect that 5-AzaC had on repetitive element expression was also assessed. Here, 46 repeats were found differentially transcribed between 5-AzaC-treated and control females with long terminal repeat (LTR) and DNA transposon classes being amongst the most significant. This study demonstrates that the anti-fecundity activity of 5-AzaC affects more than just DNA methylation in schistosome parasites. Further characterisation of these processes may reveal novel targets for schistosomiasis control.

Genome-wide prediction of prokaryotic two-component system networks using a sequence-based meta-predictor

BackgroundTwo component systems (TCS) are signalling complexes manifested by a histidine kinase (receptor) and a response regulator (effector). They are the most abundant signalling pathways in prokaryotes and control a wide range of biological processes. The pairing of these two components is highly specific, often requiring costly and time-consuming experimental characterisation. Therefore, there is considerable interest in developing accurate prediction tools to lessen the burden of experimental work and cope with the ever-increasing amount of genomic information.ResultsWe present a novel meta-predictor, MetaPred2CS, which is based on a support vector machine. MetaPred2CS integrates six sequence-based prediction methods: in-silico two-hybrid, mirror-tree, gene fusion, phylogenetic profiling, gene neighbourhood, and gene operon. To benchmark MetaPred2CS, we also compiled a novel high-quality training dataset of experimentally deduced TCS protein pairs for k-fold cross validation, to act as a gold standard for TCS partnership predictions. Combining individual predictions using MetaPred2CS improved performance when compared to the individual methods and in comparison with a current state-of-the-art meta-predictor.ConclusionWe have developed MetaPred2CS, a support vector machine-based metapredictor for prokaryotic TCS protein pairings. Central to the success of MetaPred2CS is a strategy of integrating individual predictors that improves the overall prediction accuracy, with the in-silico two-hybrid method contributing most to performance. MetaPred2CS outperformed other available systems in our benchmark tests, and is available online at http://metapred2cs.ibers.aber.ac.uk, along with our gold standard dataset of TCS interaction pairs.

Natural depletion of H1 in sex cells causes DNA demethylation, heterochromatin decondensation and transposon activation

Transposable elements (TEs), the movement of which can damage the genome, are epigenetically silenced in eukaryotes. Intriguingly, TEs are activated in the sperm companion cell – vegetative cell (VC) – of the flowering plant Arabidopsis thaliana. However, the extent and mechanism of this activation are unknown. Here we show that about 100 heterochromatic TEs are activated in VCs, mostly by DEMETER-catalyzed DNA demethylation. We further demonstrate that DEMETER access to some of these TEs is permitted by the natural depletion of linker histone H1 in VCs. Ectopically expressed H1 suppresses TEs in VCs by reducing DNA demethylation and via a methylation-independent mechanism. We demonstrate that H1 is required for heterochromatin condensation in plant cells and show that H1 overexpression creates heterochromatic foci in the VC progenitor cell. Taken together, our results demonstrate that the natural depletion of H1 during male gametogenesis facilitates DEMETER-directed DNA demethylation, heterochromatin relaxation, and TE activation.

Corrigendum to ‘the anti-fecundity effect of 5-azacytidine (5-AzaC) on Schistosoma mansoni is linked to dis-regulated transcription, translation and stem cell activities’ [Int. J. Parasitol. Drugs and Drug Resist. 8 (2018) 213–222]

Citation for published version (APA): Geyer, K. K., Munshi, S. E., Vickers, M., Squance, M., Wilkinson, T., Berrar, D., ... Hoffmann, K. (2018). Corrigendum to ‘the anti-fecundity effect of 5-azacytidine (5-AzaC) on Schistosoma mansoni is linked to disregulated transcription, translation and stem cell activities’: [Int. J. Parasitol. Drugs and Drug Resist. 8 (2018) 213–222]. International Journal for Parasitology: Drugs and Drug Resistance, 8(3), 493. https://doi.org/10.1016/j.ijpddr.2018.07.002

MetaPred2CS: a sequence-based meta-predictor for protein–protein interactions of prokaryotic two-component system proteins

MOTIVATION Two-component systems (TCS) are the main signalling pathways of prokaryotes, and control a wide range of biological phenomena. Their functioning depends on interactions between TCS proteins, the specificity of which is poorly understood. RESULTS The MetaPred2CS web-server interfaces a sequence-based meta-predictor specifically designed to predict pairing of the histidine kinase and response-regulator proteins forming TCSs. MetaPred2CS integrates six sequence-based methods using a support vector machine classifier and has been intensively tested under different benchmarking conditions: (i) species specific gene sets; (ii) neighbouring versus orphan pairs; and (iii) k-fold cross validation on experimentally validated datasets. AVAILABILITY AND IMPLEMENTATION Web server at: http://metapred2cs.ibers.aber.ac.uk/, Source code: https://github.com/martinjvickers/MetaPred2CS or implemented as Virtual Machine at: http://metapred2cs.ibers.aber.ac.uk/download CONTACT: naf4@aber.ac.ukSupplementary information: Supplementary data are available at Bioinformatics online.

Observing the Moon: The Modern Astronomer's Guide, Second Edition

Even before the ancient Greeks invented optical lenses, humans peered into the heavens with wonder. Notable figures such as Galileo and Isaac Newton are among the more famous astronomers who have helped humanity understand the solar system and our place within it. The study of the Moon has enhanced our understanding of the solar system, including our own planet. The Moon, in addition to being a fascinating feature in the night sky, has prompted great works of art and literature the world over.