| Doctorant : |
Xue ZHAO
|
| Directeur de thèse : |
Leila TIRICHINE ,
Directrice de recherche CNRS |
| Financement : |
Chinese Scholarship Council (CSC) |
| Date de la soutenance : |
mardi 15 décembre 2020, 09h00 |
| Modalité : |
- Lieu : Salle de réunion, bâtiment 25, campus Lombarderie
|
| Jury : |
- Président de jury : Marianne Delarue, Professeure, Université Paris Sud
- Rapporteur : Célia Barroux, Professeure, Université de Zurich
- Rapporteur : Jean-Luc Mouget, Professeur, Université du Mans
- Examinateur : Jean-Marc Celton, Maître de Conférences, Université d'Angers
- Directeur de thèse :
Leila TIRICHINE ,
Directrice de recherche CNRS
|
Diatoms are one of the ecologically most successful eukaryotic phytoplankton in the world. They are abundant in a wide range of habitats, their physiology, plasticity and fast adaptation to different environmental conditions help them dominate modern Oceans. Compared to genetic regulation, epigenetic changes can be flexible and reversible and histone modifications are one of the epigenetic mechanisms which can impact gene expression. Phaeodactylum tricornutum (P. tricornutum) is one of the model diatom species, also the first unicellular organism with a full repertoire of post-translational modifications of histones, which makes it an ideal species to study epigenetic regulation in single celled organisms. In this thesis manuscript, I focus on histone modification mechanisms in P. tricornutum, utilize classical reverse genetic method: knockout of candidate genes to identify the catalytic enzyme which is responsible of the deposition of histone modifications. Polycomb group protein (PcG) complexes are evolutionarily conserved epigenetic regulatory components that act antagonistically with Trithorax (TrxG) complexes to regulate genes which are involved in cell differentiation and development. In the first chapter we investigated the diversity of PcG and TrxG genes in marine unicellular species, report the correlation of these epigenetic modifiers and environmental factor for the first time, also emphasise the unique co-occurrence pattern of histone marks in P. tricornutum. Based on those discoveries, further study with chapter two and three focused on two PcG complexes, PRC2 and PRC1. In total, three core components of PcG protein were identified in PRC1 and PRC2 complex respectively, the second part of thesis explored the unique function of PRC2 and its associated mark H3K27me3 which I report related to morphology in P. tricornutum. Chapter three discussed the crosstalk between H3K27me3 and H2AK119Ubi which is deposited by PRC1. The last chapter describes a novel histone modification detected in P. tricornutum was found conserved among eukaryotes. The last chapter reports the characterization of this novel mark and identification of the histone writer.
Publications
2021
Zhao, Xue; Rastogi, Achal; Cabanillas, Anne Flore Deton; Mohamed, Ouardia Ait; Cantrel, Catherine; Lombard, Berangère; Murik, Omer; Genovesio, Auguste; Bowler, Chris; Bouyer, Daniel; Loew, Damarys; Lin, Xin; Veluchamy, Alaguraj; Vieira, Fabio Rocha Jimenez; Tirichine, Leila
Genome wide natural variation of H3K27me3 selectively marks genes predicted to be important for cell differentiation in Phaeodactylum tricornutum Article de journal
Dans: New Phytologist, p. nph.17129, 2021, ISSN: 0028-646X.
@article{Zhao2020b,
title = {Genome wide natural variation of H3K27me3 selectively marks genes predicted to be important for cell differentiation in Phaeodactylum tricornutum},
author = {Xue Zhao and Achal Rastogi and Anne Flore {Deton Cabanillas} and Ouardia {Ait Mohamed} and Catherine Cantrel and Berangère Lombard and Omer Murik and Auguste Genovesio and Chris Bowler and Daniel Bouyer and Damarys Loew and Xin Lin and Alaguraj Veluchamy and Fabio Rocha Jimenez Vieira and Leila Tirichine},
url = {https://onlinelibrary.wiley.com/doi/10.1111/nph.17129},
doi = {10.1111/nph.17129},
issn = {0028-646X},
year = {2021},
date = {2021-01-01},
urldate = {2020-12-01},
journal = {New Phytologist},
pages = {nph.17129},
publisher = {Blackwell Publishing Ltd},
abstract = {In multicellular organisms, Polycomb Repressive Complex2 (PRC2) is known to deposit tri-methylation of lysine 27 of histone H3 (H3K27me3) to establish and maintain gene silencing, critical for developmentally regulated processes. The PRC2 complex is absent in both widely studied model yeasts, which initially suggested that PRC2 arose with the emergence of multicellularity. However, its discovery in several unicellular species including microalgae questions its role in unicellular eukaryotes. Here, we use Phaeodactylum tricornutum enhancer of zeste E(z) knockouts and show that P. tricornutum E(z) is responsible for di- and tri-methylation of lysine 27 of histone H3. H3K27me3 depletion abolishes cell morphology in P. tricornutum providing evidence for its role in cell differentiation. Genome-wide profiling of H3K27me3 in fusiform and triradiate cells further revealed genes that may specify cell identity. These results suggest a role for PRC2 and its associated mark in cell differentiation in unicellular species, and highlight their ancestral function in a broader evolutionary context than currently is appreciated.},
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In multicellular organisms, Polycomb Repressive Complex2 (PRC2) is known to deposit tri-methylation of lysine 27 of histone H3 (H3K27me3) to establish and maintain gene silencing, critical for developmentally regulated processes. The PRC2 complex is absent in both widely studied model yeasts, which initially suggested that PRC2 arose with the emergence of multicellularity. However, its discovery in several unicellular species including microalgae questions its role in unicellular eukaryotes. Here, we use Phaeodactylum tricornutum enhancer of zeste E(z) knockouts and show that P. tricornutum E(z) is responsible for di- and tri-methylation of lysine 27 of histone H3. H3K27me3 depletion abolishes cell morphology in P. tricornutum providing evidence for its role in cell differentiation. Genome-wide profiling of H3K27me3 in fusiform and triradiate cells further revealed genes that may specify cell identity. These results suggest a role for PRC2 and its associated mark in cell differentiation in unicellular species, and highlight their ancestral function in a broader evolutionary context than currently is appreciated.
2020
Ait-Mohamed, Ouardia; Vanclová, Anna M G Novák; Joli, Nathalie; Liang, Yue; Zhao, Xue; Genovesio, Auguste; Tirichine, Leila; Bowler, Chris; Dorrell, Richard G
PhaeoNet: A Holistic RNAseq-Based Portrait of Transcriptional Coordination in the Model Diatom Phaeodactylum tricornutum Article de journal
Dans: Frontiers in Plant Science, vol. 11, 2020, ISSN: 1664462X.
@article{Ait-Mohamed2020,
title = {PhaeoNet: A Holistic RNAseq-Based Portrait of Transcriptional Coordination in the Model Diatom Phaeodactylum tricornutum},
author = {Ouardia Ait-Mohamed and Anna M G {Novák Vanclová} and Nathalie Joli and Yue Liang and Xue Zhao and Auguste Genovesio and Leila Tirichine and Chris Bowler and Richard G Dorrell},
url = {https://pubmed.ncbi.nlm.nih.gov/33178253/},
doi = {10.3389/fpls.2020.590949},
issn = {1664462X},
year = {2020},
date = {2020-10-01},
journal = {Frontiers in Plant Science},
volume = {11},
publisher = {Frontiers Media S.A.},
abstract = {Transcriptional coordination is a fundamental component of prokaryotic and eukaryotic cell biology, underpinning the cell cycle, physiological transitions, and facilitating holistic responses to environmental stress, but its overall dynamics in eukaryotic algae remain poorly understood. Better understanding of transcriptional partitioning may provide key insights into the primary metabolism pathways of eukaryotic algae, which frequently depend on intricate metabolic associations between the chloroplasts and mitochondria that are not found in plants. Here, we exploit 187 publically available RNAseq datasets generated under varying nitrogen, iron and phosphate growth conditions to understand the co-regulatory principles underpinning transcription in the model diatom Phaeodactylum tricornutum. Using WGCNA (Weighted Gene Correlation Network Analysis), we identify 28 merged modules of co-expressed genes in the P. tricornutum genome, which show high connectivity and correlate well with previous microarray-based surveys of gene co-regulation in this species. We use combined functional, subcellular localization and evolutionary annotations to reveal the fundamental principles underpinning the transcriptional co-regulation of genes implicated in P. tricornutum chloroplast and mitochondrial metabolism, as well as the functions of diverse transcription factors underpinning this co-regulation. The resource is publically available as PhaeoNet, an advanced tool to understand diatom gene co-regulation.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Transcriptional coordination is a fundamental component of prokaryotic and eukaryotic cell biology, underpinning the cell cycle, physiological transitions, and facilitating holistic responses to environmental stress, but its overall dynamics in eukaryotic algae remain poorly understood. Better understanding of transcriptional partitioning may provide key insights into the primary metabolism pathways of eukaryotic algae, which frequently depend on intricate metabolic associations between the chloroplasts and mitochondria that are not found in plants. Here, we exploit 187 publically available RNAseq datasets generated under varying nitrogen, iron and phosphate growth conditions to understand the co-regulatory principles underpinning transcription in the model diatom Phaeodactylum tricornutum. Using WGCNA (Weighted Gene Correlation Network Analysis), we identify 28 merged modules of co-expressed genes in the P. tricornutum genome, which show high connectivity and correlate well with previous microarray-based surveys of gene co-regulation in this species. We use combined functional, subcellular localization and evolutionary annotations to reveal the fundamental principles underpinning the transcriptional co-regulation of genes implicated in P. tricornutum chloroplast and mitochondrial metabolism, as well as the functions of diverse transcription factors underpinning this co-regulation. The resource is publically available as PhaeoNet, an advanced tool to understand diatom gene co-regulation.
Zhao, Xue; Hoguin, Antoine; Chaumier, Timothée; Tirichine, Leila
Epigenetic control of diatom genomes: An overview from in Silico characterisation to functional studies Chapitre d'ouvrage
Dans: The molecular life of diatoms, Springer Nature Switzerland AG, 2020.
@inbook{cEQ5:ZHAO_TIRICHINE:2020,
title = {Epigenetic control of diatom genomes: An overview from in Silico characterisation to functional studies},
author = {Xue Zhao and Antoine Hoguin and Timothée Chaumier and Leila Tirichine},
year = {2020},
date = {2020-04-01},
booktitle = {The molecular life of diatoms},
publisher = {Springer Nature Switzerland AG},
keywords = {},
pubstate = {published},
tppubtype = {inbook}
}
Zhao, Xue; Cabanillas, Anne Flore Deton; Veluchamy, Alaguraj; Bowler, Chris; Vieira, Fabio Rocha Jimenez; Tirichine, Leila
Probing the Diversity of Polycomb and Trithorax Proteins in Cultured and Environmentally Sampled Microalgae Article de journal
Dans: Frontiers in Marine Science, vol. 7, p. 189, 2020, ISSN: 2296-7745.
@article{10.3389/fmars.2020.00189,
title = {Probing the Diversity of Polycomb and Trithorax Proteins in Cultured and Environmentally Sampled Microalgae},
author = {Xue Zhao and Anne Flore {Deton Cabanillas} and Alaguraj Veluchamy and Chris Bowler and Fabio Rocha Jimenez Vieira and Leila Tirichine},
url = {https://www.frontiersin.org/article/10.3389/fmars.2020.00189},
doi = {10.3389/fmars.2020.00189},
issn = {2296-7745},
year = {2020},
date = {2020-01-01},
journal = {Frontiers in Marine Science},
volume = {7},
pages = {189},
abstract = {Polycomb (PcG) and Trithorax (TrxG) complexes are two evolutionarily conserved epigenetic regulatory components that act antagonistically to regulate the expression of genes involved in cell differentiation and development in multicellular organisms. The absence of PcG in both yeast models Saccharomyces cerevisiae and Schizosaccharomyces pombe suggested that polycomb proteins might have evolved together with the emergence of multicellular organisms. However, high throughput sequencing of several microalgal genomes and transcriptomes reveals an unprecedented abundance and diversity of genes encoding the components of these complexes. We report here the diversity of genes encoding PcG and TrxG proteins in microalgae from the Marine Microbial Eukaryote Transcriptome Sequencing Project database (MMETSP) and detected at broad scale in Tara Oceans genomics datasets using a highly sensitive method called eDAF (enhanced Domain Architecture Filtering). Further, we explored the correlation between environmental factors measured during the Tara Oceans expedition and transcript levels of PcG and TrxG components. PcG and TrxG are responsible for the deposition of a number of histone marks among which a TrxG associated mark, H3K4me3 which we profiled genome wide in the model diatom Phaeodactylum tricornutum to understand its role in microalgae and revisited the previously published histone code and co-occurrence with other histone marks including the antagonizing Polycomb deposited mark H3K27me3.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Polycomb (PcG) and Trithorax (TrxG) complexes are two evolutionarily conserved epigenetic regulatory components that act antagonistically to regulate the expression of genes involved in cell differentiation and development in multicellular organisms. The absence of PcG in both yeast models Saccharomyces cerevisiae and Schizosaccharomyces pombe suggested that polycomb proteins might have evolved together with the emergence of multicellular organisms. However, high throughput sequencing of several microalgal genomes and transcriptomes reveals an unprecedented abundance and diversity of genes encoding the components of these complexes. We report here the diversity of genes encoding PcG and TrxG proteins in microalgae from the Marine Microbial Eukaryote Transcriptome Sequencing Project database (MMETSP) and detected at broad scale in Tara Oceans genomics datasets using a highly sensitive method called eDAF (enhanced Domain Architecture Filtering). Further, we explored the correlation between environmental factors measured during the Tara Oceans expedition and transcript levels of PcG and TrxG components. PcG and TrxG are responsible for the deposition of a number of histone marks among which a TrxG associated mark, H3K4me3 which we profiled genome wide in the model diatom Phaeodactylum tricornutum to understand its role in microalgae and revisited the previously published histone code and co-occurrence with other histone marks including the antagonizing Polycomb deposited mark H3K27me3.