During the past half century, evidence for inheritance of variable traits has accumulated from experiments in plants and animals and epidemiological studies in humans. Here, we summarize some of the reported cases of epigenetic inheritance and the proposed mechanisms involved in the transmission of non-genetic information between generations in plants, nematodes, flies and mammals. It has long been accepted that information is epigenetically inherited in plants. Although many questions regarding the underlying mechanisms remain to be answered, it is now evident that epigenetic mechanisms are also responsible for the transmission of phenotypes in animals. We highlight similarities and differences between models and species.
Mechanisms of epigenetic inheritance of variable traits through the germline
Reproduction2020, 159(6) .
Blay N, Casas E, Galvan-Femenia, Graffelman J, deCid R, Vavouri T
Assessment of kinship detection using RNA-seq data
bioRxiv13 Feb 2019, On-line preprint . Epub 13 Feb 2019
Analysis of RNA sequencing (RNA-seq) data from related individuals is widely used in clinical and molecular genetics studies. Sample labelling mistakes are estimated to affect more than 4% of published samples. Therefore, as a method of data quality control, a way to reconstruct pedigrees from RNA-seq data would be useful for confirming the expected relationships. Currently, reconstruction of pedigrees is based mainly on SNPs or microsatellites, obtained from genotyping arrays, whole genome sequencing and whole exome sequencing. Potential problems with using RNA-seq data for kinship detection are the low proportion of the genome that it covers, the highly skewed coverage of exons of different genes depending on expression level and allele-specific expression. In this study we assess the use of RNA-seq data to detect kinship between individuals, through pairwise identity-by-descent (IBD) estimates. First, we obtained high quality SNPs after successive filters to minimize the effects due to allelic imbalance as well as errors in sequencing, mapping and genotyping. Then, we used these SNPs to calculate pairwise IBD estimates. By analysing both real and simulated RNA-seq data we show that it is possible to identify up to second degree relationships using RNA-seq data of even low to moderate sequencing depth.
Lu TT, Heyne S, Dror E, Casas E, Leonhardt L, Boenke T, Yang CH, Arrigoni L, Dalgaard K, Teperino R, Enders L, Selvaraj M, Ruf M, Raja SJ, Xie H, Boenisch U, Orkin SH, Lynn FC, Hoffman BG, Grün D, Vavouri T, Lempradl AM, Pospisilik JA
The Polycomb-Dependent Epigenome Controls β Cell Dysfunction, Dedifferentiation, and Diabetes.
Cell Metab.4 May 2018, . Epub 4 May 2018
To date, it remains largely unclear to what extent chromatin machinery contributes to the susceptibility and progression of complex diseases. Here, we combine deep epigenome mapping with single-cell transcriptomics to mine for evidence of chromatin dysregulation in type 2 diabetes. We find two chromatin-state signatures that track β cell dysfunction in mice and humans: ectopic activation of bivalent Polycomb-silenced domains and loss of expression at an epigenomically unique class of lineage-defining genes. β cell-specific Polycomb (Eed/PRC2) loss of function in mice triggers diabetes-mimicking transcriptional signatures and highly penetrant, hyperglycemia-independent dedifferentiation, indicating that PRC2 dysregulation contributes to disease. The work provides novel resources for exploring β cell transcriptional regulation and identifies PRC2 as necessary for long-term maintenance of β cell identity. Importantly, the data suggest a two-hit (chromatin and hyperglycemia) model for loss of β cell identity in diabetes.
Book1 Jan 2018, 1766(Methods in Molecular Biology book series) .
This detailed volume examines bioinformatic and molecular biological methods useful to identify and to explore the functions of CpG islands, key navigation points to understand gene regulation in fundamental processes such as development and cell differentiation as well as in diseases like cancer. Beginning with a historical perspective and important properties of CpG islands, the book continues with sections on computational and wet lab methods related to the study of DNA methylation, and in-depth protocols for the analysis of CpG island functional features including epigenetic profiling and chromatin interactions. Written for the highly successful Methods in Molecular Biology series, chapters include introductions to their respective topics, lists of the necessary materials and reagents, step-by-step, readily reproducible protocols, and tips on troubleshooting and avoiding known pitfalls.
Authoritative and practical, CpG Islands: Methods and Protocols aims to provide readers with the information and methodologies necessary to continue to decipher how a genome’s structure and organization contribute to regulate biological processes.
Keywords: CpG dinucleotides Gene regulation Bioinformatics Computational methods DNA methylation Epigenetics Chromatin interactions
Manils J, Fischer H, Climent J, Casas E, García-Martínez C, Bas J, Sukseree S, Vavouri T, Ciruela F, de Anta JM, Tschachler E, Eckhart L, Soler C
Double deficiency of Trex2 and DNase1L2 nucleases leads to accumulation of DNA in lingual cornifying keratinocytes without activating inflammatory responses.
Sci Rep19 Sep 2017, 7(1)11902. Epub 19 Sep 2017
The cornification of keratinocytes on the surface of skin and oral epithelia is associated with the degradation of nuclear DNA. The endonuclease DNase1L2 and the exonuclease Trex2 are expressed specifically in cornifying keratinocytes. Deletion of DNase1L2 causes retention of nuclear DNA in the tongue epithelium but not in the skin. Here we report that lack of Trex2 results in the accumulation of DNA fragments in the cytoplasm of cornifying lingual keratinocytes and co-deletion of DNase1L2 and Trex2 causes massive accumulation of DNA fragments throughout the cornified layers of the tongue epithelium. By contrast, cornification-associated DNA breakdown was not compromised in the epidermis. Aberrant retention of DNA in the tongue epithelium was associated neither with enhanced expression of DNA-driven response genes, such as Ifnb, Irf7 and Cxcl10, nor with inflammation. Of note, the expression of Tlr9, Aim2 and Tmem173, key DNA sensor genes, was markedly lower in keratinocytes and keratinocyte-built tissues than in macrophages and immune tissues, and DNA-driven response genes were not induced by introduction of DNA in keratinocytes. Altogether, our results indicate that DNase1L2 and Trex2 cooperate in the breakdown and degradation of DNA during cornification of lingual keratinocytes and aberrant DNA retention is tolerated in the oral epithelium.
Klosin A, Reis K, Hidalgo-Carcedo C, Casas E, Vavouri T, Lehner B
Impaired DNA replication derepresses chromatin and generates a transgenerationally inherited epigenetic memory.
Sci AdvAug 2017, 3(8)e1701143. Epub 16 Aug 2017
Impaired DNA replication is a hallmark of cancer and a cause of genomic instability. We report that, in addition to causing genetic change, impaired DNA replication during embryonic development can have major epigenetic consequences for a genome. In a genome-wide screen, we identified impaired DNA replication as a cause of increased expression from a repressed transgene in Caenorhabditis elegans. The acquired expression state behaved as an "epiallele," being inherited for multiple generations before fully resetting. Derepression was not restricted to the transgene but was caused by a global reduction in heterochromatin-associated histone modifications due to the impaired retention of modified histones on DNA during replication in the early embryo. Impaired DNA replication during development can therefore globally derepress chromatin, creating new intergenerationally inherited epigenetic expression states.
Klosin A, Casas E, Hidalgo-Carcedo C, Vavouri T, Lehner B
Transgenerational transmission of environmental information in C. elegans.
Science21 Apr 2017, 356(6335)320-323.
The environment experienced by an animal can sometimes influence gene expression for one or a few subsequent generations. Here, we report the observation that a temperature-induced change in expression from a Caenorhabditis elegans heterochromatic gene array can endure for at least 14 generations. Inheritance is primarily in cis with the locus, occurs through both oocytes and sperm, and is associated with altered trimethylation of histone H3 lysine 9 (H3K9me3) before the onset of zygotic transcription. Expression profiling reveals that temperature-induced expression from endogenous repressed repeats can also be inherited for multiple generations. Long-lasting epigenetic memory of environmental change is therefore possible in this animal.
Jordà M, Díez-Villanueva A, Mallona I, Martín B, Lois S, Barrera V, Esteller M, Vavouri T, Peinado MA
The epigenetic landscape of Alu repeats delineates the structural and functional genomic architecture of colon cancer cells.
Genome Res.Jan 2017, 27(1)118-132. Epub 20 Dec 2016
Cancer cells exhibit multiple epigenetic changes with prominent local DNA hypermethylation and widespread hypomethylation affecting large chromosomal domains. Epigenome studies often disregard the study of repeat elements owing to technical complexity and their undefined role in genome regulation. We have developed NSUMA (Next-generation Sequencing of UnMethylated Alu), a cost-effective approach allowing the unambiguous interrogation of DNA methylation in more than 130,000 individual Alu elements, the most abundant retrotransposon in the human genome. DNA methylation profiles of Alu repeats have been analyzed in colon cancers and normal tissues using NSUMA and whole-genome bisulfite sequencing. Normal cells show a low proportion of unmethylated Alu (1%-4%) that may increase up to 10-fold in cancer cells. In normal cells, unmethylated Alu elements tend to locate in the vicinity of functionally rich regions and display epigenetic features consistent with a direct impact on genome regulation. In cancer cells, Alu repeats are more resistant to hypomethylation than other retroelements. Genome segmentation based on high/low rates of Alu hypomethylation allows the identification of genomic compartments with differential genetic, epigenetic, and transcriptomic features. Alu hypomethylated regions show low transcriptional activity, late DNA replication, and its extent is associated with higher chromosomal instability. Our analysis demonstrates that Alu retroelements contribute to define the epigenetic landscape of normal and cancer cells and provides a unique resource on the epigenetic dynamics of a principal, but largely unexplored, component of the primate genome.
Manils J, Casas E, Viña-Vilaseca A, López-Cano M, Díez-Villanueva A, Gómez D, Marruecos L, Ferran M, Benito C, Perrino FW, Vavouri T, de Anta JM, Ciruela F, Soler C
The Exonuclease Trex2 Shapes Psoriatic Phenotype.
J. Invest. Dermatol.Dec 2016, 136(12)2345-2355. Epub 27 Jun 2016
Trex2 is a keratinocyte-specific 3'-deoxyribonuclease that participates in the maintenance of skin homeostasis after DNA damage. Here, we show that this exonuclease is strongly upregulated in human psoriasis, a hyperproliferative and inflammatory skin disease. Similarly, the imiquimod (IMQ)- and Il23-induced mouse psoriasis was associated with a substantial upregulation of Trex2, which was recruited into fragmented chromatin in keratinocytes that were undergoing impaired proliferation, differentiation, and cell death, indicating an important role in DNA processing. Using Trex2 knockout mice, we have found that Trex2 deficiency attenuated IMQ-induced psoriasis-like skin inflammation and enhanced IMQ-induced parakeratosis. Also, Il23-induced ear swelling was diminished in Trex2 knockout mice in comparison with wild-type (wt) mice. Transcriptome analysis identified multiple genes that were deregulated by Trex2 loss after treatment with IMQ. Specifically, immune response genes and pathways normally associated with inflammation were downregulated, whereas those related to skin differentiation and chromatin biology showed increased expression. Interestingly, Trex2 deficiency led to decreased IMQ-induced keratinocyte death via both cell autonomous and noncell autonomous mechanisms. Hence, our data indicate that Trex2 acts as a critical factor in the pathogenesis of psoriasis by promoting keratinocyte apoptosis and enucleation and thereby influencing skin immune responses.