The influence of DNA methylation on monoallelic expression

© 2019 The Author(s). This is an open access article published by Portland Press Limited on behalf of the Biochemical Society and distributed under the Creative Commons Attribution License 4.0 (CC BY-NC-ND).Monoallelic gene expression occurs in diploid cells when only one of the two alleles of a gene is active. There are three main classes of genes that display monoallelic expression in mammalian genomes: (1) imprinted genes that are monoallelically expressed in a parent-of-origin dependent manner; (2) X-linked genes that undergo random X-chromosome inactivation in female cells; (3) random monoallelically expressed single and clustered genes located on autosomes. The heritability of monoallelic expression patterns during cell divisions implies that epigenetic mechanisms are involved in the cellular memory of these expression states. Among these, methylation of CpG sites on DNA is one of the best described modification to explain somatic inheritance. Here, we discuss the relevance of DNA methylation for the establishment and maintenance of monoallelic expression patterns among these three groups of genes, and how this is intrinsically linked to development and cellular states.This work was supported by Fundação para a Ciência e Tecnologia (FCT)/Ministério da Ciência, Tecnologia e Ensino Superior (MCTES), Portugal, through the project grants PTDC/BEX-BCM/2612/2014 and PTDC/BIA-MOL/29320/2017 IC&DT. S.T.d.R. has a CEECUIND/01234/207 assistant research contract from FCT. A.-V.G. is supported by an INSERM investigator position. Publications costs were supported by UID/BIM/50005/2019, project funded by FCT/MCTES through Fundos do Orçamento de Estado.info:eu-repo/semantics/publishedVersio

X-Chromosome Inactivation and Autosomal Random Monoallelic Expression as “Faux Amis”

Funding: The work of NK and VMB was funded by iNOVA4Health – UIDB/Multi/04462/2020 and UIDP/Multi/04462/2020, a program financially supported by Fundação para a Ciência e Tecnologia (FCT)/Ministério da Educação e Ciência through national funds, and the FCT grant PTDC/BEX-BCM/5900/2014. CFA-P has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No. 752806. A-VG was supported by Fundação para a Ciência e Tecnologia (FCT), Portugal, through an assistant research contract (CEECIND/02085/2018) and the project grant PTDC/MEDOUT/4301/2020 IC&DT.X-chromosome inactivation (XCI) and random monoallelic expression of autosomal genes (RMAE) are two paradigms of gene expression regulation where, at the single cell level, genes can be expressed from either the maternal or paternal alleles. X-chromosome inactivation takes place in female marsupial and placental mammals, while RMAE has been described in mammals and also other species. Although the outcome of both processes results in random monoallelic expression and mosaicism at the cellular level, there are many important differences. We provide here a brief sketch of the history behind the discovery of XCI and RMAE. Moreover, we review some of the distinctive features of these two phenomena, with respect to when in development they are established, their roles in dosage compensation and cellular phenotypic diversity, and the molecular mechanisms underlying their initiation and stability.publishersversionpublishe

Imprinting fidelity in mouse iPSCs depends on sex of donor cell and medium formulation

Funding Information: We would like to thank Sérgio de Almeida, Miguel Casanova and Inês Milagre for critical reading of the manuscript, and the members of the S.T.d.R.’s team for helpful discussions. We also thank Tânia Carvalho and Pedro Ruivo for their help in histological analysis; Judith Webster at Babraham Institute for LC-MS measurements; Bethan Hussey at Sanger Sequencing and Kristina Tabbada at Babraham Institute for assistance with high-throughput sequencing; and the Bioimaging unit as well as Andreia Santos, Rute Gonçalves and Mariana Fernandes of the Flow Cytometry Facility of Instituto de Medicina Molecular João Lobo Antunes for their services and assistance. Work in S.T.d.R.’s team was supported by Fundação para a Ciência e Tecnologia (FCT) Ministério da Ciência, Tecnologia e Ensino Superior (MCTES), Portugal [IC&DT projects PTDC/BEX-BCM/2612/2014 and PTDC/BIA-MOL/29320/2017 as well as projects UIDB/04565/2020 and UIDP/04565/2020 of the Research Unit Institute from Bioengineering and Biosciences – iBB and LA/P/0140/2020 of the Associate Laboratory Institute for Health and Bioeconomy – i4HB]; S.T.d.R. and A.-V.G. are supported by assistant research contracts from FCT/MCTES (CEECIND/01234/2017 and CEECIND/02085/2018, respectively); M.A and A.C.R. are supported, respectively, by SFRH/BD/151251/2021 and SFRH/BD/137099/2018 PhD fellowships from FCT/MCTES. J.V.G.L is supported by COVID/BD/152624/2022 from FCT/MCTES. MAE-M was supported by a BBSRC Discovery Fellowship (BB/T009713/1) and is now supported by a Snow Medical Fellowship. F.K. is supported by the Babraham Institute Strategic Core Funding and A.M. by BBSRC BBS/E/B/000C0421. B.B.J. work was funded by Fundação para a Ciência e Tecnologia (FCT), and FEDER, LISBOA-01-0145-FEDER-028534, project co-funded by FEDER, through POR Lisboa 2020—Programa Operacional Regional de Lisboa. T.K. is supported by Janko Jamnik Doctoral Scholarship from National Institute of Chemistry. Funding Information: We would like to thank Sérgio de Almeida, Miguel Casanova and Inês Milagre for critical reading of the manuscript, and the members of the S.T.d.R.’s team for helpful discussions. We also thank Tânia Carvalho and Pedro Ruivo for their help in histological analysis; Judith Webster at Babraham Institute for LC-MS measurements; Bethan Hussey at Sanger Sequencing and Kristina Tabbada at Babraham Institute for assistance with high-throughput sequencing; and the Bioimaging unit as well as Andreia Santos, Rute Gonçalves and Mariana Fernandes of the Flow Cytometry Facility of Instituto de Medicina Molecular João Lobo Antunes for their services and assistance. Work in S.T.d.R.’s team was supported by Fundação para a Ciência e Tecnologia (FCT) Ministério da Ciência, Tecnologia e Ensino Superior (MCTES), Portugal [IC&DT projects PTDC/BEX-BCM/2612/2014 and PTDC/BIA-MOL/29320/2017 as well as projects UIDB/04565/2020 and UIDP/04565/2020 of the Research Unit Institute from Bioengineering and Biosciences – iBB and LA/P/0140/2020 of the Associate Laboratory Institute for Health and Bioeconomy – i4HB]; S.T.d.R. and A.-V.G. are supported by assistant research contracts from FCT/MCTES (CEECIND/01234/2017 and CEECIND/02085/2018, respectively); M.A and A.C.R. are supported, respectively, by SFRH/BD/151251/2021 and SFRH/BD/137099/2018 PhD fellowships from FCT/MCTES. J.V.G.L is supported by COVID/BD/152624/2022 from FCT/MCTES. MAE-M was supported by a BBSRC Discovery Fellowship (BB/T009713/1) and is now supported by a Snow Medical Fellowship. F.K. is supported by the Babraham Institute Strategic Core Funding and A.M. by BBSRC BBS/E/B/000C0421. B.B.J. work was funded by Fundação para a Ciência e Tecnologia (FCT), and FEDER, LISBOA-01-0145-FEDER-028534, project co-funded by FEDER, through POR Lisboa 2020—Programa Operacional Regional de Lisboa. T.K. is supported by Janko Jamnik Doctoral Scholarship from National Institute of Chemistry. Publisher Copyright: © 2022, The Author(s).Reprogramming of somatic cells into induced Pluripotent Stem Cells (iPSCs) is a major leap towards personalised approaches to disease modelling and cell-replacement therapies. However, we still lack the ability to fully control the epigenetic status of iPSCs, which is a major hurdle for their downstream applications. Epigenetic fidelity can be tracked by genomic imprinting, a phenomenon dependent on DNA methylation, which is frequently perturbed in iPSCs by yet unknown reasons. To try to understand the causes underlying these defects, we conducted a thorough imprinting analysis using IMPLICON, a high-throughput method measuring DNA methylation levels, in multiple female and male murine iPSC lines generated under different experimental conditions. Our results show that imprinting defects are remarkably common in iPSCs, but their nature depends on the sex of donor cells and their response to culture conditions. Imprints in female iPSCs resist the initial genome-wide DNA demethylation wave during reprogramming, but ultimately cells accumulate hypomethylation defects irrespective of culture medium formulations. In contrast, imprinting defects on male iPSCs depends on the experimental conditions and arise during reprogramming, being mitigated by the addition of vitamin C (VitC). Our findings are fundamental to further optimise reprogramming strategies and generate iPSCs with a stable epigenome.publishersversionpublishe

Independent mechanisms target SMCHD1 to trimethylated histone H3 lysine 9-modified chromatin and the inactive X chromosome

The chromosomal protein SMCHD1 plays an important role in epigenetic silencing at diverse loci, including the inactive X chromosome, imprinted genes, and the facioscapulohumeral muscular dystrophy locus. Although homology with canonical SMC family proteins suggests a role in chromosome organization, the mechanisms underlying SMCHD1 function and target site selection remain poorly understood. Here we show that SMCHD1 forms an active GHKL-ATPase homodimer, contrasting with canonical SMC complexes, which exist as tripartite ring structures. Electron microscopy analysis demonstrates that SMCHD1 homodimers structurally resemble prokaryotic condensins. We further show that the principal mechanism for chromatin loading of SMCHD1 involves an LRIF1-mediated interaction with HP1γ at trimethylated histone H3 lysine 9 (H3K9me3)-modified chromatin sites on the chromosome arms. A parallel pathway accounts for chromatin loading at a minority of sites, notably the inactive X chromosome. Together, our results provide key insights into SMCHD1 function and target site selection

Smchd1-Dependent and -Independent Pathways Determine Developmental Dynamics of CpG Island Methylation on the Inactive X Chromosome

X chromosome inactivation involves multiple levels of chromatin modification, established progressively and in a stepwise manner during early development. The chromosomal protein Smchd1 was recently shown to play an important role in DNA methylation of CpG islands (CGIs), a late step in the X inactivation pathway that is required for long-term maintenance of gene silencing. Here we show that inactive X chromosome (Xi) CGI methylation can occur via either Smchd1-dependent or -independent pathways. Smchd1-dependent CGI methylation, the primary pathway, is acquired gradually over an extended period, whereas Smchd1-independent CGI methylation occurs rapidly after the onset of X inactivation. The de novo methyltransferase Dnmt3b is required for methylation of both classes of CGI, whereas Dnmt3a and Dnmt3L are dispensable. Xi CGIs methylated by these distinct pathways differ with respect to their sequence characteristics and immediate chromosomal environment. We discuss the implications of these results for understanding CGI methylation during development

The tandem repeat modules of Xist lncRNA: a swiss army knife for the control of X-chromosome inactivation

© 2021 The Author(s) This is an open access article published by Portland Press Limited on behalf of the Biochemical Society and distributed under the Creative Commons Attribution License 4.0 (CC BY).X-inactive-specific transcript (Xist) is a long non-coding RNA (lncRNA) essential for X-chromosome inactivation (XCI) in female placental mammals. Thirty years after its discovery, it is still puzzling how this lncRNA triggers major structural and transcriptional changes leading to the stable silencing of an entire chromosome. Recently, a series of studies in mouse cells have uncovered domains of functional specialization within Xist mapping to conserved tandem repeat regions, known as Repeats A-to-F. These functional domains interact with various RNA binding proteins (RBPs) and fold into distinct RNA structures to execute specific tasks in a synergistic and coordinated manner during the inactivation process. This modular organization of Xist is mostly conserved in humans, but recent data point towards differences regarding functional specialization of the tandem repeats between the two species. In this review, we summarize the recent progress on understanding the role of Xist repetitive blocks and their involvement in the molecular mechanisms underlying XCI. We also discuss these findings in the light of the similarities and differences between mouse and human Xist.This work was supported by Fundação para a Ciência e Tecnologia (FCT)/Ministério da Ciência, Tecnologia e Ensino Superior (MCTES) through the project grants PTDC/BIA-MOL/29320/2017 (S.T.d.R. and A.C.R.), and PTDC/BTM-TEC/28534/2017 (M.C.). S.T.d.R. and A.-V. G. are supported by assistant research contracts from FCT/MCTES (CEECIND/01234/2017 and CEECIND/02085/2018, respectively; A.C.R. is supported by a PhD fellowship from FCT/MCTES (SFRH/BD/137099/2018).info:eu-repo/semantics/publishedVersio

Random monoallelic expression of genes on autosomes: Parallels with X-chromosome inactivation

International audienceGenes are generally expressed from their two alleles, except in some particular cases such as random inactivation of one of the two X chromosomes in female mammals or imprinted genes which are expressed only from the maternal or the paternal allele. A lesser-known phenomenon is random monoallelic expression (RME) of autosomal genes, where genes can be stably expressed in a monoallelic manner, from either one of the parental alleles. Studies on autosomal RME face several challenges. First, RME that is based on epigenetic mechanisms has to be distinguished from biased expression of one allele caused by a DNA sequence polymorphism in a regulatory element. Second, RME should not be confused with transient monoallelic expression often observed in single cell analyses, and that often corresponds to dynamic bursting of expression. Thanks to analyses on clonal cell populations, the existence of RME in cultured cells is now well established. Future studies of RME in vivo will have to overcome tissue heterogeneity and certain technical limitations. Here, we discuss current knowledge on autosomal RME, as well as possible mechanisms controlling these expression patterns and potential implications for development and disease, drawing parallels with what is known for X-chromosome inactivation, a paradigm of random monoallelic expression

Changes in 5S rDNA Chromatin Organization and Transcription during Heterochromatin Establishment in Arabidopsis

International audienceIn the Arabidopsis accession Columbia, 5S rDNA is located in the pericentromeric heterochromatin of chromosomes 3, 4, and 5. Both a major and some minor 5S rRNA species are expressed from chromosomes 4 and 5, whereas the genes on chromosome 3 are not transcribed. Here, we show that 5S rDNA methylation is reduced in 2-day-old seedlings versus 4-day-old or older aerial plant tissues, and the minor 5S rRNA species are expressed most abundantly at this stage. Similarly, when 5S rDNA is demethylated by 5-azacytidine treatment or via the decrease in DNA methylation1 (ddm1) mutation, the expression of minor 5S rRNA species is increased. We also show that in leaf nuclei of mature wild-type plants, the transcribed fraction of 5S rDNA forms loops that emanate from chromocenters. These loops, which are enlarged in nuclei of mature ddm1 plants, are enriched for histone H3 acetylated at Lys-9 and methylated at Lys-4 compared with the heterochromatic chromocenters. Up to 4 days after germination, heterochromatin is not fully developed: the 5S rDNA resides in prechromocenters, does not form conspicuous loops, and shows the lowest transcription level. Our results indicate that the expression and chromatin organization of 5S rRNA genes change during heterochromatin establishment