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Measuring stress-induced DNA methylation in apomictic Dandelions
Gurp, Thomas P. van - \ 2017
Wageningen University. Promotor(en): Wim van der Putten, co-promotor(en): K.J.F. Verhoeven; A. Biere. - Wageningen : Wageningen University - ISBN 9789463436045 - 176
taraxacum officinale - epigenetics - dna methylation - inheritance - apomixis - environmental factors - epigenetica - dna-methylering - overerving - milieufactoren
The success or continuous existence of species requires continuous adaptation to changes in the environment to survive and contribute offspring to the next generation. Selection acts on the phenotype, which is in turn determined by the complex interplay of genetic, epigenetic and environmental variation. (Natural) selection leads to ‘survival of the fittest’ or best-adapted individuals to their local environment, ultimately determining which individuals contribute offspring to the next generation. Understanding the mechanisms by which epigenetic and genetic variation can arise and get passed on through generations determines our understanding of inheritance and evolution. Hitherto, the mechanistic understanding of genetics has shaped the scientific view of inheritance and evolution, leading to the gene-centered paradigm of Neo-Darwinism. However, recent studies indicate that besides genetic (DNA sequence) variation, epigenetic variation can also be transmitted between generations. Further studies on the properties and transgenerational dynamics of epigenetic variation are needed to enhance our understanding of heritability and evolution.
Epigenetic variation has distinct properties and different transgenerational dynamics compared to genetic variation. Epigenetic variation helps to regulate gene expression and determines the different cell types and function in eukaryotes. The main function of DNA methylation, an important part of the epigenetic code, is to prevent the spread of selfish genetic elements in the genome and to establish the different cellular profiles observed in multicellular organisms. One differentiating feature of epigenetic variation compared to genetic variation is that (specific) epigenetic variation can arise under the influence of stress. This can enable a trans-generational stress-response of organisms which can have a positive influence on the phenotype and (natural) selection on either the (enhanced level of) transgenerational phenotypic plasticity or the epigenetic variation itself, potentially influencing natural selection and ultimately evolution. Where genetic variation can be characterized as hard-inheritance, the inheritance of epigenetic variation is often referred to as ‘soft-inheritance’ due to the lower transgenerational stability and resetting that occurs in the intergenerational transfer of epigenetic variation. Epigenetic variation is also often dependent on, or a downstream consequence, of genetic variation, suggesting that it is (in part) determined by genetic variation.
Mechanistic studies in model species have contributed greatly to the understanding of the molecular mechanisms that control the dynamics of different epigenetic marks present in multicellular organisms. In plants, studies in the model plant Arabidopsis thaliana have resulted in deciphering the most important molecular mechanisms and actors, giving an ever-increasing insight into the dynamics of epigenetic regulation of cells and organisms. A key feature of model systems is the ability to ‘switch’ off certain genes or molecular pathways, for instance via the experimental use of mutants, enabling the study of their role in the heritability of epigenetic marks. DNA methylation is a well-studied epigenetic mark, which has shown high stability even in transgenerational experiments.
From the perspective of studying epigenetic variation, plants are particularly interesting for several reasons, most importantly: 1) The separation between soma and germline, the Weismann barrier, is less strict in plants compared to other eukaryotes, as in higher plants
germline cells are formed during floral development from somatic cells (which can occur throughout the life of the plant), whereas in most eukaryotes germline cell development is restricted to a defined point (early) in the organismal development. 2) The sessile nature of plants makes an adaptive plastic response to changing environments an important feature, a plant cannot just walk away when the going gets tough. 3) The transgenerational stability of DNA methylation is higher in plants compared to other eukaryotes such as mammals, in which epigenetic information is erased during germline reprogramming. These factors combined suggest that the potential importance of epigenetic variation in plants might be high.
In this thesis, I focus on studying DNA methylation in apomictic Dandelions, applying Next Generation Sequencing (NGS) approaches to the study of this non-model plant species. Apomictic dandelions produce seeds that are genetically identical to the ‘mother’ plant, which makes it easier to study the influence of epigenetic variation without confounding effects of genetic variation. Working with Next Generation Sequencing data is still relatively new and therefore not always optimized for specific types of analysis. I discovered a distinct error pattern in RNAseq data that indicated an artificial source of variation that could be traced back to the way the RNAseq libraries were constructed. The first publication of this thesis contains a technical analysis of such artefacts present in RNAseq data, suggesting that these errors are related to random hexamer mispriming during library construction (Chapter 2).
The main goal of my work is to better understand the role of epigenetic variation in adaptation and plasticity of plants. This role remains poorly understood. This is in part due to the lack of high-resolution techniques that allow for the detailed study of epigenetic marks such as DNA methylation in non-model organisms. Existing techniques for measuring DNA methylation such as methylation sensitive AFLPs offer only information on DNA methylation variation in an anonymous and limited fashion. The plummeting costs of sequencing techniques have enabled large-scale genotyping efforts (focusing on genetic variation only) for a wide variety of non-model organisms. Here, I extended this popular genotyping by sequencing technique, to allow for sequencing-based epigenotyping or epiGBS (chapter 3), which allows for measuring DNA methylation and genetic variation in hundreds of samples simultaneously. I have extensively validated the approach, providing evidence that with the right design, the accuracy of the DNA methylation measurements with epiGBS are as high as those with the gold standard Whole Genome Bisulfite Sequencing.
An important aim of my PhD research was to investigate the stability of (stress induced) DNA methylation variation in apomictic dandelions and the potential of phenotypic variation underpinned by DNA methylation variation to be subjected to selection. I therefore studied the transgenerational stability of both stress induced and natural DNA methylation variation in different genotypes of apomictic dandelions in a six-generation experiment, comparing DNA methylation patterns between generations and tracking changes in them (chapter 4) using epiGBS. I found clear but limited evidence for environmental induction of heritable DNA methylation changes after application of Jasmonic Acid. Furthermore, I found a significant negative relation between the similarity of DNA methylation patterns and intergenerational distance, indicating epigenetic divergence over generations. I conclude that DNA methylation in both CG and CHG (where H can be any nucleotide except for G) sequence context are heritable and that environmental perturbation can result in heritable DNA methylation changes which are however not widespread.
A prerequisite for epigenetic variation to contribute to adaptation is that epigenetic variants that affect the phenotype are heritable. To test whether an epigenetics-based selection response is possible, at least over the time course of a few generations, I selected early flowering for two subsequent generations in three genotypes of apomictic dandelions. This selection effort included lines that received a stress pre-treatment with either Jasmonic Acid or 5-azacytidine, to determine if stress-induced DNA methylation variation would increase the capacity to respond to selection. The selection experiment on flowering time (chapter 5) resulted in a shift in flowering time for all treatments in a young apomict, suggesting that natural and heritable epigenetic variation can underpin quantitative traits such as flowering time. I also found evidence for treatment induced (epi)genetic variation leading to a stronger selection response in one out of 3 genotypes. This suggests that stress- induced heritable epigenetic variation can lead to a selection response. Further study is however required to rule out genetic variants and to study the long-term stability of the variation selected upon.
Finally, in the General Discussion I summarize the findings, putting them in context with recently published studies. I reflect on the state of the field of ecological epigenetics and in what sense the epiGBS technique that I developed and other emerging techniques can contribute to a better understanding of the role of epigenetic variation in ecology and evolution. I reflect on the place of epiGBS compared to other techniques. I point out that with the growing evidence of the inadequacy and misinterpretation of MS-AFLP results a systematic review of such results by replicating the studies employing sequencing based techniques such as epiGBS instead of MS-AFLP is in order.
Epigenetic inheritance in apomictic dandelions : stress-induced and heritable modifications in DNA methylation and small RNA
Preite, V. - \ 2016
Wageningen University. Promotor(en): Wim van der Putten, co-promotor(en): K.J.F. Verhoeven. - Wageningen : Wageningen University - ISBN 9789462578715 - 152
taraxacum officinale - epigenetics - inheritance - apomixis - dna methylation - rna - heritability - stress - epigenetica - overerving - dna-methylering
Epigenetic variation, such as changes in DNA methylations, regulatory small RNAs (sRNAs) and chromatin modifications can be induced by environmental stress. There is increasing information that such induced epigenetic modifications can be transmitted to offspring, potentially mediating adaptive transgenerational responses to environmental changes. However, it is unclear if this phenomenon is common and relevant for adaptation under natural conditions. My thesis study aimed to examine epigenetic inheritance in common and widespread apomictic dandelions (Taraxacum officinale Wig.). Due to their asexual reproduction mode by producing clonal seeds offspring from seeds are genetically uniform and thus suitable to investigate epigenetic effects that are not confounded with genetic variation.
I exposed apomictic dandelion lineages to drought and salicylic acid (SA) stress, which induces plant defense responses following pathogen attack, and found effects on patterns of DNA methylation up to two stress-free offspring generations after exposure. However, a heritable stress signal was not present in all tests and was stress- and lineage-dependent. Drought stress triggered a weak and lineage-dependent signal that was lost again in the second offspring generation. SA treatment revealed a stress-related increased rate of DNA methylation changes in the two offspring generations, but no stress signal was found in the stressed generation itself. I also observed changes in small RNA production due the drought and SA stress experienced two generations ago. These transgenerational sRNA effects showed association with gene functions related to grandparental drought and SA stress, which suggests functional relevance of the transgenerational effects.
I used a reciprocal transplantation field experiment to investigate whether exposing dandelions to natural field stresses also triggers DNA methylation changes. The experiment revealed evidence of adaptive divergence between the populations, suggesting that non-native habitats are experienced as more stressful. However, under these field conditions no induction-based DNA methylation changes were found that persisted into offspring.
By using AFLP and MS-AFLP screening of natural apomictic dandelion populations across a north-south transect in Europe I examined if natural, heritable DNA methylation variation reflects underlying genetic variation, or if it shows patterns that are not predictable from underlying genetics. I found that a large part of heritable DNA methylation differentiation along the north-south transect was correlated with genetic differentiation. However, a fraction of differentiation in heritable DNA methylation was independent from genetic variation. This suggests a potential of epigenetics to play an evolutionary role independently, at least to some extent, from underlying genetics. Overall, I found indications of epigenetic inheritance in apomictic dandelions. Whether epigenetic variation would result in adaptive phenotypic variation in nature and whether it would persist long enough to play a relevant role in adaptation remains unclear and requires further study.
Adventitious root formation in Arabidopsis : underlying mechanisms and applications
Massoumi, Mehdi - \ 2016
Wageningen University. Promotor(en): Richard Visser, co-promotor(en): Geert-Jan de Klerk; Frans Krens. - Wageningen : Wageningen University - ISBN 9789462578524 - 191
arabidopsis thaliana - adventitious roots - formation - plant development - quantitative traits - etiolation - auxins - explants - molecular biology - gene expression - dna methylation - rooting - ontogeny - plant breeding - adventiefwortels - formatie - plantenontwikkeling - kwantitatieve kenmerken - etiolering - auxinen - explantaten - moleculaire biologie - genexpressie - dna-methylering - beworteling - ontogenie - plantenveredeling
Adventitious root (AR) formation is indispensable in vegetative propagation and is widely used. A better understanding of the underlying mechanisms is needed to improve rooting treatments. We first established a system to study rooting in Arabidopsis, the model organism in plant biology but only occasionally used to study adventitious rooting. Inhibition of polar auxin transport reduced AR formation. The role of auxin transporter proteins (several PIN-proteins) was found to be tissue-specific. Maturation (the transition from juvenile to adult) negatively influenced AR formation. Maturation was associated with increased DNA methylation and decreased miR156 level. 5-Azacytidine, a drug that reduces DNA methylation, increased rooting. We also examined the effect of two donor plant pre-treatments, etiolation and flooding, on rooting. Both increased AR formation.
Persistent organic pollutants : aberrant DNA methylation underlying potential health effects
Dungen, M.W. van den - \ 2016
Wageningen University. Promotor(en): Tinka Murk; Ellen Kampman, co-promotor(en): Wilma Steegenga; Dieuwertje Kok. - Wageningen : Wageningen University - ISBN 9789462577893 - 207 p.
persistent organic pollutants - dna methylation - molecular genetics - epigenetics - health hazards - toxic substances - endocrine disruptors - eels - fish consumption - toxicology - persistente organische verontreinigende stoffen - dna-methylering - moleculaire genetica - epigenetica - gezondheidsgevaren - toxische stoffen - hormoonverstoorders - palingen - visconsumptie - toxicologie
Wild caught fish, especially marine fish, can contain high levels of persistent organic pollutants (POPs). In the Netherlands, especially eel from the main rivers have high POP levels. This led to a ban in 2011 on eel fishing due to health concerns. Many of the marine POPs have been related to adverse health effects such as endocrine disruption, neurodevelopmental problems, immune suppression and cancer. Although some mechanisms of action of POPs are clear, like dioxins binding to the aryl hydrocarbon receptor and OH-PCBs binding to thyroid transport proteins, not all adverse health effects can be explained by these mechanisms of action. Epigenetic phenomena, such as DNA methylation, have been proposed as a possible molecular mechanism underlying adverse health effects. DNA methylation is a heritable modification, which refers to the addition of a methyl group to cytosine in a CpG dinucleotide. Observational studies have indeed shown that POPs can affect global DNA methylation, although results are inconsistent. Some animal studies as well as in vitro experiments suggest that POPs can affect gene-specific DNA methylation, however, the biological significance and relevance for humans is not clear. Therefore, this thesis aimed to 1) study the accumulation of POPs in men consuming eel from high-polluted areas 2) elucidate whether seafood-related POPs can induce aberrant DNA methylation and 3) to determine whether DNA methylation is related to functional endpoints and gene expression in vitro.
For this purpose eight POPs that are abundantly present in seafood were chosen, namely 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), polychlorobiphenyl (PCB) 126 and 153, perfluorooctanesulfonic acid (PFOS), hexabromocyclododecane (HBCD), 2,2′,4,4′- tetrabromodiphenyl ether (BDE-47), tributyltin (TBT), and methylmercury (MeHg). Chapter 2 describes the in vitro effects of these POPs and mixtures thereof in H295R adrenocortical carcinoma cells. Relative responses for 13 steroid hormones and 7 genes involved in the steroidogenic pathway, and CYP1A1, were analysed. PFOS induced the most pronounced effects on steroid hormone levels by significantly affecting 9 out of 13 hormone levels measured, with the largest increases found for 17β-estradiol, corticosterone, and cortisol. Furthermore, TCDD, both PCBs, and TBT significantly altered steroidogenesis. Increased steroid hormone levels were accompanied by related increased gene expression levels. The differently expressed genes were MC2R, CYP11B1, CYP11B2, and CYP19A1 and changes in gene expression levels were more sensitive than changes in hormone levels. The POP mixtures tested showed mostly additive effects, especially for DHEA and 17β-estradiol levels. This study shows that some seafood POPs are capable of altering steroidogenesis in H295R cells at concentrations that mixtures might reach in human blood, suggesting that adverse health effects cannot be excluded. DNA methylation was not measured in this study due to the short exposure time, which was expected not to be sufficient for long-term epigenetic marks. Therefore, in chapters 3A and 3B a differentiation experiment was performed enabling long-term exposure to POPs. Human mesenchymal stem cells (hMSCs) were differentiated into mature adipocytes over a time-course of 10 days. The transcriptional regulatory cascade involved in adipocyte differentiation has been extensively studied, however the mechanisms driving the transcription are poorly understood. In chapter 3A we therefore first explored the involvement of DNA methylation in transcriptional regulation during adipocyte differentiation. Genome-wide changes in DNA methylation were measured as well as the expression of adipogenic genes. The majority of these genes showed significant expression changes during the differentiation process. There were, however, only a couple of these differentially expressed genes that were differentially methylated. Genome-wide DNA methylation changes were most often located in intergenic regions, and underrepresented close to the transcription start site. This suggested that changes in DNA methylation are not the underlying mechanism regulating gene expression during adipocyte differentiation. Nevertheless, we explored DNA methylation differences after continuous exposure to POPs to investigate whether this could be an underlying mechanism by which POPs affect adipocyte differentiation. TCDD and PFOS decreased lipid accumulation, while TBT increased lipid accumulation. TCDD and TBT induced opposite gene expression profiles, whereas after PFOS exposure gene expression remained relatively stable. Genome-wide DNA methylation analysis showed that all three POPs affected DNA methylation patterns in adipogenic and other genes, but without concomitant gene expression changes. Differential methylation was again predominantly detected in intergenic regions, where the biological relevance of alterations in DNA methylation is unclear. This study demonstrated that POPs, at environmentally relevant levels, are able to induce differential DNA methylation in differentiating adipocytes. However, the biological relevance of this aberrant DNA methylation remains unclear.
The in vitro results showed a proof of principle that POPs could be capable of altering DNA methylation. To this date, no human studies were performed investigating the relationship between POP levels and genome-wide DNA methylation. In order to investigate this, we first measured POP levels in eel consumers from the high-polluted areas (areas with a ban on eel fishing) and compared these levels to men consuming eel from low-polluted areas or aquaculture (chapter 4). We aimed to investigate the accumulation of these POPs and determine whether the predictions made in an earlier risk assessment were valid. This was indeed the case as levels of dioxins and dioxin-like compounds were on average 2.5 times higher in men consuming eel from high-polluted areas. Furthermore, PCBs with their hydroxylated metabolites, and perfluoroalkyl substances (PFASs) were, up to ten times, higher in these consumers. Especially the high levels of dioxins and dioxin-like compounds as well as the OH-PCBs are expected to be of health concern. We continued this research in chapter 5 by associating all the measured POPs to clinical parameters related to e.g. thyroid hormones and liver enzymes, but found no relationship. Subsequently, we investigated the association between dioxins and dioxin-like compounds, the sum of seven indicator PCBs, and PFOS with genome-wide DNA methylation. We detected a number of differentially methylated regions (DMRs) related to genes involved in carcinogenesis (e.g. BRCA1, MAGEE2, HOXA5), the immune system (e.g. RNF39, HLA-DQB1), in retinol homeostasis (DHRS4L2), or in metabolism (CYP1A1). In contrast to the in vitro data, most significant effects were detected in CpG islands and were annotated close to the promoter region. This suggests that the differential methylation might be related to differential expression and possibly induce adverse health effects. The hypermethylation of some of these gene related to cancer could be an explanation of the carcinogenic effects that are observed with POP exposure.
Based on the results of this thesis we can conclude that the consumption of eel from high-polluted areas lead to accumulation of POPs above safe levels and that POP levels are associated with gene-specific DNA methylation in vitro as well as in environmentally exposed men. More research, however, is needed to fully elucidate the biological implications of this aberrant DNA methylation. A first step can be to measure histone modifications, as these two epigenetic marks together are likely better in predicting gene expression. The second step can be to investigate the potential health effects related to these epigenetic marks and to determine whether there is a causal relationship. Although at this point there is a lack of knowledge with regard to health effects caused by DNA methylation, the consumption of eel from these high-polluted areas is ill- advised, because adverse health effects cannot be excluded based on our results and can even be expected based on literature.
Natural epigenetic variation contributes to heritable flowering divergence in a widespread asexual dandelion lineage
Wilschut, Rutger ; Oplaat, C. ; Snoek, L.B. ; Kirschner, J. ; Verhoeven, K.J.F. - \ 2016
Molecular Ecology 25 (2016)8. - ISSN 0962-1083 - p. 1759 - 1768.
dna methylation - epigenetic inheritance - apomixis - asexual reproduction - adaptation
Epigenetic variation has been proposed to contribute to the success of asexual plants, either as a contributor to phenotypic plasticity or by enabling transient adaptation via selection on transgenerationally stable, but reversible, epialleles. While recent studies in experimental plant populations have shown the potential for epigenetic mechanisms to contribute to adaptive phenotypes, it remains unknown if heritable variation in ecologically relevant traits is at least partially epigenetically determined in natural populations. Here, we tested the hypothesis that DNA methylation variation contributes to heritable differences in flowering time within a single widespread apomictic clonal lineage of the common dandelion (Taraxacum officinale s. lat.). Apomictic clone members of the same apomictic lineage collected from different field sites showed heritable differences in flowering time, which was correlated with inherited differences in methylation-sensitive AFLP marker profiles. Differences in flowering between apomictic clone members were significantly reduced after in vivo de-methylation using the DNA methyltransferase inhibitor zebularine. This synchronization of flowering times suggests that flowering time divergence within an apomictic lineage was mediated by differences in DNA methylation. While the underlying basis of the methylation polymorphism at functional flowering time-affecting loci remains to be demonstrated, our study shows that epigenetic variation contributes to heritable phenotypic divergence in ecologically relevant traits in natural plant populations. This result also suggests that epigenetic mechanisms can facilitate adaptive divergence within genetically uniform asexual lineages.
Opportunities of New Plant Breeding Techniques
Schaart, Jan ; Riemens, M.M. ; Wiel, C.C.M. van de; Lotz, L.A.P. ; Smulders, M.J.M. - \ 2015
Wageningen : Wageningen UR - 24
plantenveredeling - plantenveredelingsmethoden - resistentieveredeling - cisgenese - intragenic recombination - mutagenese - dna-methylering - bloei - plant breeding - plant breeding methods - resistance breeding - cisgenesis - mutagenesis - dna methylation - flowering
This brochure gives an overview of new plant breeding techniques. This overview is based on a more technical review of the scientific literature, published in a separate report. The overview presents the opportunities and limitations of these techniques from the point of view of potential applications in plant breeding with promising results for improving agricultural sustainability.
Epigenetic Basis of Morphological Variation and Phenotypic Plasticity in Arabidopsis thaliana
Kooke, R. ; Johannes, F. ; Wardenaar, R. ; Becker, F.F.M. ; Etcheverry, M. ; Colot, V. ; Vreugdenhil, D. ; Keurentjes, J.J.B. - \ 2015
The Plant Cell 27 (2015)2. - ISSN 1040-4651 - p. 337 - 348.
quantitative trait loci - dna methylation - transcription factor - qtl analysis - population - plant - inheritance - stability - evolution - performance
Epigenetics is receiving growing attention in the plant science community. Epigenetic modifications are thought to play a particularly important role in fluctuating environments. It is hypothesized that epigenetics contributes to plant phenotypic plasticity because epigenetic modifications, in contrast to DNA sequence variation, are more likely to be reversible. The population of decrease in DNA methylation 1-2 (ddm1-2)-derived epigenetic recombinant inbred lines (epiRILs) in Arabidopsis thaliana is well suited for studying this hypothesis, as DNA methylation differences are maximized and DNA sequence variation is minimized. Here, we report on the extensive heritable epigenetic variation in plant growth and morphology in neutral and saline conditions detected among the epiRILs. Plant performance, in terms of branching and leaf area, was both reduced and enhanced by different quantitative trait loci (QTLs) in the ddm1-2 inherited epigenotypes. The variation in plasticity associated significantly with certain genomic regions in which the ddm1-2 inherited epigenotypes caused an increased sensitivity to environmental changes, probably due to impaired genetic regulation in the epiRILs. Many of the QTLs for morphology and plasticity overlapped, suggesting major pleiotropic effects. These findings indicate that epigenetics contributes substantially to variation in plant growth, morphology, and plasticity, especially under stress conditions
Growth regulation, imprinting, and epigenetic transcription-related gene expression differs in lung of deceased transgenic cloned and normal goats
Meng, L. ; Jia, R.X. ; Sun, Y. ; Wang, Z.Y. ; Wan, Y.J. ; Zhang, Y.L. ; Zhong, B.S. ; Wang, F. - \ 2014
Theriogenology 81 (2014)3. - ISSN 0093-691X - p. 459 - 466.
cell nuclear transfer - dna methylation - nationwide survey - tumor-suppressor - bovine clones - aberrant - calves - mice - cdkn1c - cattle
Somatic cell nuclear transfer (SCNT) is a promising technique to produce mammalian transgenic clones. Only a small proportion of manipulated embryos, however, can develop into viable offspring. The abnormal growth and development of cloned animals, furthermore, are accompanied by aberrant lung development. Our objective was to investigate molecular background of lung developmental problems in transgenic (random insertion of exogenous DNA) cloned goats. We examined expression of 15 genes involved in growth regulation, imprinting, and epigenetic transcription in lung tissue of deceased transgenic cloned and normal goats of various ages. Compared with normal goats of the same age from conventional reproduction, expression of 13 genes (BMP4, FGF10, GHR, HGFR, PDGFR, RABP, VEGF, H19, CDKNIC, PCAF, MeCP2, HDAC1, and Dnmt3b) decreased in transgenic cloned goats that died at or shortly after birth; Expression of eight genes (FGF10, PDGFR, RABP, VEGF, PCAF, HDAC1, MeCP2, and Dnmt3b) decreased in fetal death of transgenic cloned goats. Expression of two epigenetic transcription genes (PCAF and Dnmt3b) decreased in disease death of transgenic cloned goats (1-4 months old). Disruptions in gene expression might be associated with the high neonatal mortality in transgenic cloned animals. These findings have implications in understanding the low efficiency of transgenic cloning. (C) 2014 Elsevier Inc. All rights reserved.
Tomato yellow leaf curl virus resistance by ty-1 involves increased cytosine methylation of viral genomes and is compromised by cucumber mosaic virus infection
Butterbach, P.B.E. ; Verlaan, M.G. ; Dullemans, A.M. ; Lohuis, H. ; Visser, R.G.F. ; Bai, Y. ; Kormelink, R.J.M. - \ 2014
Proceedings of the National Academy of Sciences of the United States of America 111 (2014)35. - ISSN 0027-8424 - p. 12942 - 12947.
short interfering rna - dna methylation - geminivirus al2 - l2 proteins - adenosine kinase - gene - suppression - arabidopsis - plants - locus
Tomato yellow leaf curl virus (TYLCV) and related begomoviruses are a major threat to tomato production worldwide and, to protect against these viruses, resistance genes from different wild tomato species are introgressed. Recently, the Ty-1 resistance gene was identified, shown to code for an RNA-dependent RNA polymerase and to be allelic with Ty-3. Here we show that upon TYLCV challenging of resistant lines carrying Ty-1 or Ty-3, low virus titers were detected concomitant with the production of relatively high levels of siRNAs whereas, in contrast, susceptible tomato Moneymaker (MM) revealed higher virus titers but lower amounts of siRNAs. Comparative analysis of the spatial genomic siRNA distribution showed a consistent and subtle enrichment for siRNAs derived from the V1 and C3 genes in Ty-1 and Ty-3. In plants containing Ty-2 resistance the virus was hardly detectable, but the siRNA profile resembled the one observed in TYLCV-challenged susceptible tomato (MM). Furthermore, a relative hypermethylation of the TYLCV V1 promoter region was observed in genomic DNA collected from Ty-1 compared with that from (MM). The resistance conferred by Ty-1 was also effective against the bipartite tomato severe rugose begomovirus, where a similar genome hypermethylation of the V1 promoter region was discerned. However, a mixed infection of TYLCV with cucumber mosaic virus compromised the resistance. The results indicate that Ty-1 confers resistance to geminiviruses by increasing cytosine methylation of viral genomes, suggestive of enhanced transcriptional gene silencing. The mechanism of resistance and its durability toward geminiviruses under natural field conditions is discussed.
Epigenetic variation in asexually reproducing organisms
Verhoeven, K.J.F. ; Preite, V. - \ 2014
Evolution 68 (2014)3. - ISSN 0014-3820 - p. 644 - 655.
dna methylation - arabidopsis-thaliana - japanese knotweed - transgenerational plasticity - phenotypic plasticity - transposable elements - natural-populations - fallopia-japonica - mutation-rates - clonal plants
The role that epigenetic inheritance can play in adaptation may differ between sexuals and asexuals because (1) the dynamics of adaptation differ under sexual and asexual reproduction and the opportunities offered by epigenetic inheritance may affect these dynamics differently; and (2) in asexual reproduction epigenetic reprogramming mechanisms that are associated with meiosis can be bypassed, which could promote the buildup of epigenetic variation in asexuals. Here, we evaluate current evidence for an epigenetic contribution to adaptation in asexuals. We argue that two aspects of epigenetic variation should have particular relevance for asexuals, namely epigenetics-mediated phenotypic plasticity within and between generations, and heritable variation via stochastic epimutations. An evaluation of epigenetic reprogramming mechanisms suggests that some, but not all, forms of asexual reproduction enhance the likelihood of stable transmission of epigenetic marks across generations compared to sexual reproduction. However, direct tests of these predicted sexual–asexual differences are virtually lacking. Stable transmission of DNA methylation, transcriptomes, and phenotypes from parent to clonal offspring are demonstrated in various asexual species, and clonal genotypes from natural populations show habitat-specific DNA methylation. We discuss how these initial observations can be extended to demonstrate an epigenetic contribution to adaptation.
A structural equation modelling approach to explore the role of B vitamins and immune markers in lung cancer risk
Baltar, V.T. ; Xun, W.W. ; Johansson, M. ; Bueno-de-Mesquita, B. ; Boshuizen, H.C. ; Gils, C.H. van; Onland-Moret, C.N. - \ 2013
European Journal of Epidemiology 28 (2013)8. - ISSN 0393-2990 - p. 677 - 688.
one-carbon metabolism - dna methylation - indoleamine 2,3-dioxygenase - colorectal-cancer - system activation - folate - infection - men - polymorphisms - neopterin
The one-carbon metabolism (OCM) is considered key in maintaining DNA integrity and regulating gene expression, and may be involved in the process of carcinogenesis. Several B-vitamins and amino acids have been implicated in lung cancer risk, via the OCM directly as well as immune system activation. However it is unclear whether these factors act independently or through complex mechanisms. The current study applies structural equations modelling (SEM) to further disentangle the mechanisms involved in lung carcinogenesis. SEM allows simultaneous estimation of linear relations where a variable can be the outcome in one equation and the predictor in another, as well as allowing estimation using latent variables (factors estimated by correlation matrix). A large number of biomarkers have been analysed from 891 lung cancer cases and 1,747 controls nested within the European Prospective Investigation into Cancer and Nutrition (EPIC) cohort. Four putative mechanisms in the OCM and immunity were investigated in relation to lung cancer risk: methionine-homocysteine metabolism, folate cycle, transsulfuration, and mechanisms involved in inflammation and immune activation, all adjusted for tobacco exposure. The hypothesized SEM model confirmed a direct and protective effect for factors representing methionine-homocysteine metabolism (p = 0.020) and immune activation (p = 0.021), and an indirect protective effect of folate cycle (p = 0.019), after adjustment for tobacco smoking. In conclusion, our results show that in the investigation of the involvement of the OCM, the folate cycle and immune system in lung carcinogenesis, it is important to consider complex pathways (by applying SEM) rather than the effects of single vitamins or nutrients (e.g. using traditional multiple regression). In our study SEM were able to suggest a greater role of the methionine-homocysteine metabolism and immune activation over other potential mechanisms.
The genomic landscape of meiotic crossovers and gene conversions in Arabidopsis thaliana
Wijnker, T.G. ; Velikkakam James, G. ; Ding, J. ; Becker, F.F.M. ; Klasen, J.R. ; Rawat, V. ; Rowan, B.A. ; Jong, de, D.F. ; Snoo, de, C.B. ; Zapata, L. ; Jong, H. de; Ossowski, S. ; Weigel, D. ; Koornneef, M. ; Keurentjes, J.J.B. ; Schneeberger, K. - \ 2013
eLife 2 (2013). - ISSN 2050-084X
dna methylation - recombination landscape - saccharomyces-cerevisiae - short reads - yeast - meiosis - reveals - mouse - sex - populations
Knowledge of the exact distribution of meiotic crossovers (COs) and gene conversions (GCs) is essential for understanding many aspects of population genetics and evolution, from haplotype structure and long-distance genetic linkage to the generation of new allelic variants of genes. To this end, we resequenced the four products of 13 meiotic tetrads along with 10 doubled haploids derived from Arabidopsis thaliana hybrids. GC detection through short reads has previously been confounded by genomic rearrangements. Rigid filtering for misaligned reads allowed GC identification at high accuracy and revealed an ~80-kb transposition, which undergoes copy-number changes mediated by meiotic recombination. Non-crossover associated GCs were extremely rare most likely due to their short average length of ~25-50 bp, which is significantly shorter than the length of CO-associated GCs. Overall, recombination preferentially targeted non-methylated nucleosome-free regions at gene promoters, which showed significant enrichment of two sequence motifs.
Epigenetic changes and transposon reactivation in Thai rice hybrids. Molecular Breeding
Kantama, L. ; Junbuathong, S. ; Sakulkoo, J. ; Jong, J.H.S.G.M. de; Apisitwanich, S. - \ 2013
Molecular Breeding 31 (2013)4. - ISSN 1380-3743 - p. 815 - 827.
cytosine methylation - dna methylation - elements mites - genome - retrotransposons - hybridization - markers - inheritance - activation - expression
Inter- or intraspecific hybridization is the first step in transferring exogenous traits to the germplasm of a recipient crop. One of the complicating factors is the occurrence of epigenetic modifications of the hybrids, which in turn can change their gene expression and phenotype. In this study we present an analysis of epigenome changes in rice hybrids that were obtained by crossing rice cultivars, most of them of indica type and Thai origin. Comparing amplified fragment length polymorphism (AFLP) fingerprints of twenty-four cultivars, we calculated Nei’s indexes for measuring genetic relationships. Epigenetic changes in their hybrids were established using methylation-sensitive AFLP fingerprinting and transposon display of the rice transposable elements (TEs) Stowaway Os-1 and Mashu, leading to the question whether the relationship between parental genomes is a predictor of epigenome changes, TE reactivation and changes in TE methylation. Our study now reveals that the genetic relationship between the parents and DNA methylation changes in their hybrids is not significantly correlated. Moreover, genetic distance correlates only weakly with Mashu reactivation, whereas it does not correlate with Stowaway Os-1 reactivation. Our observations also suggest that epigenome changes in the hybrids are localized events affecting specific chromosomal regions and transposons rather than affecting the genomic methylation landscape as a whole. The weak correlation between genetic distance and Mashu methylation and reactivation points at only limited influence of genetic background on the epigenetic status of the transposon. Our study further demonstrates that hybridizations between and among specific japonica and indica cultivars induce both genomic DNA methylation and reactivation/methylation change in the Stowaway Os-1 and Mashu transposons. The observed epigenetic changes seem to affect the transposons in a clear manner, partly driven by stochastic processes, which may account for a broader phenotypic plasticity of the hybrids. A better understanding of the epigenome changes leading to such transposon activation can lead to the development of novel tools for more variability in future rice breeding
Transgenerational epigenetic effects on innate immunity in broilers: An underestimated field to be explored?
Berghof, T.V.L. ; Parmentier, H.K. ; Lammers, A. - \ 2013
Poultry Science 92 (2013)11. - ISSN 0032-5791 - p. 2904 - 2913.
brain gene-expression - chicken heterophils - oxidative burst - maternal antibodies - natural antibodies - dna methylation - egg-yolk - microflora - system - growth
Transgenerational epigenetics is becoming more and more important for understanding the variation of physiological responses of individuals to the environment and the inheritance of these responses based on all mechanisms other than the actual DNA nucleotide sequence. Transgenerational epigenetics is the phenomenon that the information of the environment of (usually) a female animal is translated into memory-like responses preparing the offspring. As a consequence, individuals of the next generation may show different phenotypic traits depending whether their mothers were kept under different environmental conditions. This may result in either positive or negative effects on the next-generation individuals, which is different from individuals from mothers that have been kept in a different environment. Transgenerational epigenetic effects have been proposed and indicated for specific immune (T cell and antibody) responses (especially in mammals, but also in birds) and innate immunity (nonvertebrates), but surprisingly very little is known of transgenerational effects on innate immunity in chickens. Given the short lifespan of the chicken and therefore the likely dependence of chicken on innate immune mechanisms, more attention should be given to this arm of immunity and mechanisms of inheritance including transgenerational effects that can be initiated in the breeder generation. In addition, it is becoming evident that innate immunity also underlies metabolic disorders in broilers. In the current paper, we will argue that although very little is known of transgenerational effects of innate immunity in poultry, more attention should be given to this type of study. We will illustrate examples of transgenerational epigenetics, and finally propose strategies that should reveal the presence of transgenerational epigenetic effects on innate immunity in chickens and strategies to modulate breeder birds such that these effects positively affect innate immunity of broilers. It is suggested that a mismatch between breeder environment and broiler environment may account for unwanted effects of innate immunity in the broiler
Biased Gene Fractionation and Dominant Gene Expression among the Subgenomes of Brassica rapa
Cheng, F. ; Wu, J. ; Fang, L. ; Sun, S. ; Liu, B. ; Lin, K. ; Bonnema, A.B. ; Wang, Xiaowu - \ 2012
PLoS ONE 7 (2012)5. - ISSN 1932-6203
short read alignment - arabidopsis-thaliana - dna methylation - genome sequence - duplication - evolution - polyploids - plants
Polyploidization, both ancient and recent, is frequent among plants. A ‘‘two-step theory’’ was proposed to explain the meso-triplication of the Brassica ‘‘A’’ genome: Brassica rapa. By accurately partitioning of this genome, we observed that genes in the less fractioned subgenome (LF) were dominantly expressed over the genes in more fractioned subgenomes (MFs: MF1 and MF2), while the genes in MF1 were slightly dominantly expressed over the genes in MF2. The results indicated that the dominantly expressed genes tended to be resistant against gene fractionation. By re-sequencing two B. rapa accessions: a vegetable turnip (VT117) and a Rapid Cycling line (L144), we found that genes in LF had less nonsynonymous or frameshift mutations than genes in MFs; however mutation rates were not significantly different between MF1 and MF2. The differences in gene expression patterns and on-going gene death among the three subgenomes suggest that ‘‘two-step’’ genome triplication and differential subgenome methylation played important roles in the genome evolution of B. rapa.
From nucleosome to chromosome: a dynamic organization of genetic information
Fransz, P.F. ; Jong, J.H.S.G.M. de - \ 2011
The Plant Journal 66 (2011)1. - ISSN 0960-7412 - p. 4 - 17.
histone variant h2a.z - 30-nm chromatin fiber - arabidopsis-thaliana - dna methylation - interphase chromosomes - in-vivo - nuclear architecture - insitu hybridization - regulatory regions - h4-k16 acetylation
Gene activity is controlled at different levels of chromatin organization, which involve genomic sequences, nucleosome structure, chromatin folding and chromosome arrangement. These levels are interconnected and influence each other. At the basic level nucleosomes generally occlude the DNA sequence from interacting with DNA-binding proteins. Evidently, nucleosome positioning is a major factor in gene control and chromatin organization. Understanding the biological rules that govern the deposition and removal of the nucleosomes to and from the chromatin fiber is the key to understanding gene regulation and chromatin organization. In this review we describe and discuss the relationship between the different levels of chromatin organization in plants and animals
Epigenetics, an update
Nap, J.P.H. ; Geurts van Kessel, A. - \ 2011
Wageningen : Plant Research International (Rapport / Plant Research International 397)
epigenetica - genen - dna - rna - genexpressie - dna-modificatie - dna-methylering - epigenetics - genes - gene expression - dna modification - dna methylation
Identification of imprinted genes subject to parent-of-origin specific expression in Arabidopsis thaliana seeds.
Mckeown, P.C. ; Laouielle-Duprat, S. ; Prins, J.C.P. ; Wolff, P. de; Schmid, M.W. ; Donoghue, M.T. ; Fort, A. ; Duszynska, D. ; Comte, A. ; Lao, N.T. ; Wennblom, T.J. ; Smant, G. ; Köhler, C. ; Grossniklaus, U. ; Spillane, C. - \ 2011
BMC Plant Biology 11 (2011). - ISSN 1471-2229 - 20 p.
dna methylation - transcriptome analysis - maize endosperm - life-cycle - cell-cycle - cdna-aflp - in-vivo - protein - genome - medea
Background: Epigenetic regulation of gene dosage by genomic imprinting of some autosomal genes facilitates normal reproductive development in both mammals and flowering plants. While many imprinted genes have been identified and intensively studied in mammals, smaller numbers have been characterized in flowering plants, mostly in Arabidopsis thaliana. Identification of additional imprinted loci in flowering plants by genome-wide screening for parent-of-origin specific uniparental expression in seed tissues will facilitate our understanding of the origins and functions of imprinted genes in flowering plants. Results: cDNA-AFLP can detect allele-specific expression that is parent-of-origin dependent for expressed genes in which restriction site polymorphisms exist in the transcripts derived from each allele. Using a genome-wide cDNA-AFLP screen surveying allele-specific expression of 4500 transcript-derived fragments, we report the identification of 52 maternally expressed genes (MEGs) displaying parent-of-origin dependent expression patterns in Arabidopsis siliques containing F1 hybrid seeds (3, 4 and 5 days after pollination). We identified these MEGs by developing a bioinformatics tool (GenFrag) which can directly determine the identities of transcript-derived fragments from (i) their size and (ii) which selective nucleotides were added to the primers used to generate them. Hence, GenFrag facilitates increased throughput for genome-wide cDNA-AFLP fragment analyses. The 52 MEGs we identified were further filtered for high expression levels in the endosperm relative to the seed coat to identify the candidate genes most likely representing novel imprinted genes expressed in the endosperm of Arabidopsis thaliana. Expression in seed tissues of the three top-ranked candidate genes, ATCDC48, PDE120 and MS5-like, was confirmed by Laser-Capture Microdissection and qRT-PCR analysis. Maternal-specific expression of these genes in Arabidopsis thaliana F1 seeds was confirmed via allele-specific transcript analysis across a range of different accessions. Differentially methylated regions were identified adjacent to ATCDC48 and PDE120, which may represent candidate imprinting control regions. Finally, we demonstrate that expression levels of these three genes in vegetative tissues are MET1-dependent, while their uniparental maternal expression in the seed is not dependent on MET1. Conclusions: Using a cDNA-AFLP transcriptome profiling approach, we have identified three genes, ATCDC48, PDE120 and MS5-like which represent novel maternally expressed imprinted genes in the Arabidopsis thaliana seed. The extent of overlap between our cDNA-AFLP screen for maternally expressed imprinted genes, and other screens for imprinted and endosperm-expressed genes is discussed.
Epigenetics in plant tissue culture
Smulders, M.J.M. ; Klerk, G.J.M. de - \ 2011
Plant Growth Regulation 63 (2011)2. - ISSN 0167-6903 - p. 137 - 146.
dna methylation - somaclonal variation - oil palm - micropropagated plants - histone methylation - cell culture - hop plants - musa spp. - in-vitro - bushiness
Plants produced vegetatively in tissue culture may differ from the plants from which they have been derived. Two major classes of off-types occur: genetic ones and epigenetic ones. This review is about epigenetic aberrations. We discuss recent studies that have uncovered epigenetic modifications at the molecular level, viz., changes in DNA methylation and alterations of histone methylation or acetylation. Various studies have been carried out with animals, and with plant cells or tissues that have grown in tissue culture but only little work has been done with shoots generated by axillary branching. We present various molecular methods that are being used to measure epigenetic variation. In micropropagated plants mostly differences in DNA methylation have been examined. Epigenetic changes are thought to underlie various well-known tissue-culture phenomena including rejuvenation, habituation, and morphological changes such as flower abnormalities, bushiness, and tumorous outgrowths in, among others, oil palm, gerbera, Zantedeschia and rhododendron.
Changes in genomic mythylation patterns during the formation of triploid asexuel dandelion lineages
Verhoeven, K.J.F. ; Dijk, P.J. ; Biere, A. - \ 2010
Molecular Ecology 19 (2010)2. - ISSN 0962-1083 - p. 315 - 324.
dna methylation - gene-expression - arabidopsis allotetraploids - cytosine methylation - polyploid plants - aflp markers - taraxacum - hybridization - consequences - inheritance
•DNA methylation can cause heritable phenotypic modifications in the absence of changes in DNA sequence. Environmental stresses can trigger methylation changes and this may have evolutionary consequences, even in the absence of sequence variation. However, it remains largely unknown to what extent environmentally induced methylation changes are transmitted to offspring, and whether observed methylation variation is truly independent or a downstream consequence of genetic variation between individuals.•Genetically identical apomictic dandelion (Taraxacum officinale) plants were exposed to different ecological stresses, and apomictic offspring were raised in a common unstressed environment. We used methylation-sensitive amplified fragment length polymorphism markers to screen genome-wide methylation alterations triggered by stress treatments and to assess the heritability of induced changes.•Various stresses, most notably chemical induction of herbivore and pathogen defenses, triggered considerable methylation variation throughout the genome. Many modifications were faithfully transmitted to offspring. Stresses caused some epigenetic divergence between treatment and controls, but also increased epigenetic variation among plants within treatments.•These results show the following. First, stress-induced methylation changes are common and are mostly heritable. Second, sequence-independent, autonomous methylation variation is readily generated. This highlights the potential of epigenetic inheritance to play an independent role in evolutionary processes, which is superimposed on the system of genetic inheritance