Best Poster Awards — Chromatin and Epigenetics

The 10th edition of the EMBL Conference: Chromatin and Epigentics took place virtually this year. We welcomed more than 800 participants, from which 3 were selected best poster award winners prior to the meeting and who gave a short talk on the last day of the conference. Get a glimpse of their research.

Sequence-dependent surface condensation of pioneer transcription factor on DNA

Sina Wittmann, Max Planck Institute for Molecular Cell Biology and Genetics, Germany
Presenter: Sina Wittmann, Max Planck Institute for Molecular Cell Biology and Genetics, Germany

Abstract: Biomolecular condensates are dense assemblies of proteins that are dynamic and provide distinct biochemical compartments without being surrounded by a membrane. Some, such as P granules and stress granules, behave as droplets, have many millions of molecules, and are well described by a classic phase separation picture. Others, such as transcriptional condensates are thought to form on surfaces such as DNA, are small and contain thousands of molecules. However, the correct physical description of small condensates on DNA surfaces is still under discussion. Here we investigate this question using the pioneer transcription factor Klf4. We show that Klf4 can phase separate on its own at concentrations that are above physiological, but that at lower concentrations, Klf4 only forms condensates on DNA. Analysis using optical tweezers shows that these Klf4 condensates form on DNA by a switch-like transition from a thin adsorbed layer to a thick condensed layer that is well described as a prewetting transition on a heterogeneous substrate. Condensate formation of Klf4 on DNA is thus a form of surface condensation mediated by and limited to the DNA surface. Furthermore, we are investigating how Klf4 condensation is regulated by the property of the surface such as through DNA methylation. We speculate that the prewetting transition orchestrated by pioneer transcription factors underlies the formation of transcriptional condensates in cells and provides robustness to transcription regulation.

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Single-cell profiling of histone post-translational modifications and transcription in mouse and zebrafish differentiation systems

Presenter: Kim de Luca,  Hubrecht Institute, The Netherlands
Presenter: Kim de Luca,  Hubrecht Institute, The Netherlands

Abstract: During organism development and cellular differentiation, gene expression is carefully regulated at many levels. To that end, various epigenetic mechanisms translate cell-intrinsic and -extrinsic cues into activation and repression of the relevant parts of the genome. One of the most studied and versatile forms of epigenetic regulation is the post-translational modification (PTM) of the histone proteins around which DNA is wrapped. Histone PTMs affect the surrounding DNA by forming a binding platform for a range of effector proteins, as well as by directly modulating the biophysical properties of the chromatin. Hence, histone PTMs play a crucial role in priming, establishing, and maintaining transcriptional output and cell state. Many techniques used to study histone PTMs require thousands to millions of cells, and consequently mask the heterogeneity inherent to complex biological systems. To understand the nuanced relationship between chromatin context and transcription, single-cell and multi-modal approaches are necessary. We have previously developed a method to simultaneously measure transcriptional output and DNA-protein contacts by single-cell sequencing (scDam&T). This multi-modal method is particularly suitable for studying systems containing many transient cellular states. Here, we apply scDam&T to measure chromatin modifications by expressing the E. coli DNA adenine methyltransferase (Dam) fused to a domain that specifically recognizes a histone PTM. First, we validate this approach in population and single-cell samples by comparing the resulting data to orthogonal state-of-the-art techniques. Next, using mouse embryoid bodies as an in vitro differentiation system, we apply our method to deconvolve the lineage-specific regulation of Polycomb chromatin. Finally, we study the role of H3K9me3-marked heterochromatin in the developing zebrafish embryo.

Poster not available due to unpublished data, however, you can watch a short talk presentation here.


Presenter: Moushumi Das, University of Bern, Switzerland
Presenter: Moushumi Das, University of Bern, Switzerland

Poster and abstract not available due to unpublished data.


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Best Poster Awards – The Identity and Evolution of Cell Types

The second edition of the EMBO | EMBL Symposium: The Identity and Evolution of Cell Types brought together an increased number of researchers from this growing community. 315 scientists joined the virtual meeting and enjoyed four days of talks and poster presentations streamed live. A total of 72 posters were presented at the two live poster sessions out of which three were selected as the best posters by popular vote. Take a look at the winners and their work.

Molecular fingerprinting sea anemones and jellyfish: A transcriptomic approach to characterize Cnidarian cell types
image of Alison Cole
Alison Cole, University of Vienna, Austria

Presenter: Alison Cole, University of Vienna, Austria


Animals typically consist of hundreds of different cell types, yet the evolutionary mechanisms underlying the emergence of new cell types are unclear. Cnidarians offer advantages to studies of metazoan cell type evolution, as they are the sister group to the Bilateria and yet comprise an extremely diverse set of lineages that exhibit variable life history strategies, life spans, regenerative properties, animal-defining cell types (ie. muscles and neurons), as well as clade-specific cell types (i.e. cnidocytes). Advances in single cell RNA sequencing have opened the frontiers for molecular profiling of cell types at a genome-wide scale. Application of these technologies for comparisons across species remains in its infancy, and is largely, but not exclusively, restricted to closely related species with well-defined orthologous gene sets. Here we present a large single cell dataset derived from the anthozoan polyp Nematostella vectensis (comprising both developmental and tissue-derived samples),the scyphozoan moon jelly (Aurelia aurita; comprising all life history stages as well as medusa tissue-derived samples), and the hydrozoan Clytia hemispherica (young medusa only). The same cell complement that is identifiable from species-specific genome-wide analyses is recoverable using only a set of 1:1:1 orthologous genes in all three species. Analyses of the reduced gene matrix combining all three species robustly identifies putatively homologous cell types amongst the neurosecretory derivatives, as well as cell populations with clear species-specific transcriptomic profiles. Interpretations of these data in the light of specific cell types will be discussedin order to demonstrate that the combination of unbiased single cell transcriptomes and gene-directed validations can permit the identification of novel and conserved cell types.

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Stylophora pistillata cell atlas illuminates stony coral symbiosis, calcification and immunity
Anamaria Elek, Centre for Genomic Regulation, Spain

Presenter: Anamaria Elek, Centre for Genomic Regulation, Spain


Stony corals are colonial cnidarians that sustain the most biodiverse marine ecosystems on Earth: coral reefs. Life cycle of these animals involves a swimming larva that settles and metamorphoses into a sessile polyp, which in turn develops into the adult stage, depositing in the process a protein rich organic matrix and extracellular calcium carbonate crystals to form a stony skeleton. Despite their ecological importance, little is known about the cell types and molecular pathways that underpin the biology of reef-building corals. Using single-cell RNA sequencing, we have defined over 40 cell types across the three life stages of a stony coral Stylophora pistillata. Among others, we characterized previously unknown coral immune cells, endosymbiont alga-hosting cells, and calicoblasts responsible for calcium-carbonate skeleton formation in both settling polyp and the adult coral. Apart from these specialized coral cell types, we identified evolutionary conserved cell types by phylogenetic integration of our S. pistillata cell atlas with three other available cnidarian species. These evolutionary conservations include neuronal and gland cell types, cnidaria-specific cnidocytes, and others. Overall, this study reveals the molecular and cellular basis of stony coral biology, and addresses the evolution of cell type programs in three major cnidarian lineages separated by 500 million years of evolution.

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Gene family evolution underlies cell type diversification in the hypothalamus of teleosts*
Maxwell Shafer, Biozentrum, University of Basel, Switzerland

Presenter: Maxwell ShaferBiozentrum, University of Basel, Switzerland


Hundreds of cell types form the vertebrate brain, but it is largely unknown how similar these cellular repertoires are between or within species, or how cell type diversity evolves. To examine cell type diversity across and within species, we performed single-cell RNA sequencing of ~130,000 hypothalamic cells from zebrafish (Danio rerio) and surface- and cave-morphs of Mexican tetra (Astyanax mexicanus). We found that over 75% of cell types were shared between zebrafish and Mexican tetra, which last shared a common ancestor over 150 million years ago. Orthologous cell types displayed differential paralogue expression that was generated by sub-functionalization after genome duplication. Expression of terminal effector genes, such as neuropeptides, was more conserved than the expression of their associated transcriptional regulators. Species-specific cell types were enriched for the expression of species-specific genes, and characterized by the neo-functionalization of members of recently expanded or contracted gene families. Within species comparisons revealed differences in immune repertoires and transcriptional changes in neuropeptidergic cell types associated with genomic differences between surface- and cave-morphs. The single-cell atlases presented here are a powerful resource to explore hypothalamic cell types, and reveal how gene family evolution and the neo- and sub-functionalization of paralogs contribute to cellular diversity.

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Best Poster Awards: Friend or Foe — Transcription and RNA Meet DNA Replication and Repair

During the second virtual EMBO | EMBL Symposium of the year three scientists were awarded a prize for their scientific poster. In this blog, we present the winners and their research.

Friend or Foe attracted 336 participants worldwide, discussing transcription and RNA and DNA replication and repair in live sessions and panel discussions. Three poster session rounds gave the opportunity for participants to view 72 digital posters and interact with the poster presenters.

After the sessions, a voting round followed and three presenters were distinguished with a best poster award by popular vote.

  1. Gianluca Sigismondo of the German Cancer Research Center in Heidelberg, Germany.
  2. Tycho Mevissen, Howard Hughes Medical Institute and Harvard Medical School, USA
  3. Sara Luzzi, Newcastle University, UK

Read our blog on how to create a prize-winning digital poster.

Chromatin dynamics during DNA repair investigated via chromatin-directed proteomics

A portrait picture of scientist Gianluca Sigismondo
Gianluca Sigismondo, German Cancer Research Center, Germany. PHOTO: Gianluca Sigismondo

Poster presenter: Gianluca Sigismondo

Authors: Gianluca Sigismondo, Lavinia Arseni, Jeroen Krijgsveld

DNA lesions predispose to genomic instability, a hallmark of cancer; therefore cells have evolved repair pathways to solve those harmful insults.

Double-strand breaks (DSBs) represent the most lethal DNA damage first marked by the phosphorylation of the histone H2A.X (γH2A.X) which triggers the recruitment of sensor proteins belonging to either the error-prone non-homologous end joining (NHEJ) or the efficient homologous recombination (HR) pathway.

It is now established that chromatin has an active role also in DNA repair, thus its characterization at DSB repair foci is essential to better understand the coordinate action of the repair mechanisms and to identify novel players participating in tumor-associated apoptotic resistance and cell survival.

Here we dissect chromatin changes upon exposure to ionizing radiations through multiple proteomics-based approaches. We applied the Selective Isolation of Chromatin-Associated Protein strategy (ChIP-SICAP; Rafiee, 2016) to investigate the interactors of core NHEJ, HR proteins and γH2A.X while bound to the DNA or in the chromatin soluble fraction.

Through a click chemistry-assisted procedure we profiled the configuration of DNA-bound proteins during DSBs repair; finally we analyzed the histone post-translational modifications (hPTMs) cross-talk at mono-nucleosomes marked by γH2A.X.

Our integrated analysis identified the dynamics of expected chromatin determinants during the DNA repair and interestingly suggested the role for new candidates specifically enriched upon DSB formation.

Validation experiments based on monitoring of DSB foci formation and resolution in AID-DIvA cells proficient or knock-down cells provided evidence of a role for novel candidates in DNA repair. FACS-based analysis of Traffic-light Reporter (TLR) isogenic cells upon silencing of proteins identified by MS characterized their functional role in NHEJ, HR or pathway choice. Furthermore, we defined hPTMs associated with γH2A.X-marked mono-nucleosomes and their dynamics during DSB resolution.

This analysis corroborated expected enrichments (e.g. H4K20me1/me2) and provided insights on new modifications specifically enriched at γH2A.X-nucleosomes.

Chromatin dynamics during DNA repair investigated via chromatin-directed proteomics

Towards transcription-coupled DNA repair in Xenopus egg extract

Poster presenter: Tycho Mevissen

A portrait of scientist Tycho Mevissen
Tycho Mevissen, Harvard Medical School, USA. PHOTO: Tycho Mevissen

This poster and abstract contain unpublished data and are not available at this moment.

Tycho Mevissen is a postdoctoral research fellow in Johannes Walter’s lab at Harvard Medical School. He had completed his PhD with David Komander at the MRC Laboratory of Molecular Biology in Cambridge, UK, where he used structural and biochemical tools to elucidate the intricate mechanisms of enzymes in the ubiquitin system, in particular deubiquitinases (DUBs).

His current research interests in the Walter lab revolve around molecular mechanisms at the intersection of DNA transcription, replication and repair.

In particular, he is interested in understanding how elongating RNA polymerase II deals with various types of obstacles – including different DNA lesions – during transcription elongation. To study this, he uses Xenopus egg extract, which is a powerful cell-free system that has been successfully used to recapitulate a wide range of cellular DNA repair pathways.

RBMX enables productive RNA processing of ultra long exons important for genome stability

A portrait picture of scientist Sara Luzzi
Sara Luzzi, Newcastle University, UK. PHOTO: Sara Luzzi

Poster presenter: Sara Luzzi

Authors: Sara Luzzi, Gerald Hysenaj, Chileleko Siachisumo, Kathleen Cheung, Matthew Gazzara, Katherine James, Caroline Dalgliesh, Mahsa Kheirollahi Chadegani, Ingrid Ehrmann, Graham R Smith, Simon J Cockell, Jennifer Munkley, Yoseph Barash, and David J Elliott.

The nuclear RNA binding protein RBMX has a direct role in genome repair and is required for expression of the tumour suppressor BRCA2. Here we report that RBMX controls RNA processing of key genes involved in genome maintenance in breast cancer cells.

Our data demonstrate that RBMX represses a premature polyadenylation site that would truncate BRCA2 protein, and is essential for full-length mRNA expression from other genes important for genome stability. These include ETAA1, which encodes for a key replication fork protein, where RBMX and its protein interaction partner Tra2ß efficiently suppress a weak splice site to enable ETAA1 protein expression.

More generally, we propose that RBMX facilitates correct inclusion of unusually long exons within mature mRNAs by repressing cryptic RNA processing. Our data provide new molecular insights explaining the role of RBMX in DNA repair and genome maintenance.

Poster RBMX enables productive RNA processing of ultra-long exons important for genome stability

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Best Poster Awards – In Situ Structural Biology Workshop

The EMBO Workshop: In Situ Structural Biology: From Cryo-EM to Integrative Modelling was our final virtual conference of 2020, but there was no trace of Zoom fatigue amongst the 466 participants who joined us from 6 – 8 December!

80 international researchers presented their posters during the two posters sessions on the following topics:

  • Biophysical analysis in cells
  • COVID-19
  • Imaging across scales
  • Integrative modelling
  • Molecular sociology
  • Structural analysis in situ
  • Structural biology

Each of the participants had the chance to vote for their favourite poster, resulting in two posters winning the Best Poster Award kindly sponsored by EMBO Press.  Here are the winners:

New insights on the catalytic mechanism of arsenite oxidase

PHOTO: Filipa Engrola

Authors: Filipa Engrola, Márcia Correia, Teresa Santos-Silva, Maria Romao, (UCIBIO@FCT-NOVA, Portugal)

Arsenic (As) and antimony (Sb) are two metalloids that, due to anthropogenic and natural causes, pose an environmental  threat, considered as priority pollutants by the World Health Organisation and the United States Environmental Protection Agency. Although the safety guards recommend a maximum of 10 μg/L of As and Sb in drinking water, these values are exceeded in many regions worldwide, with no remediation approach that is simultaneously effective, clean and economically sustainable [1,2]. The ancient bioenergetic enzyme arsenite oxidase (Aio), from microorganisms Rhizobium sp. NT-26 (NT-26 Aio) and Alcaligenes faecalis (A.f. Aio), is currently being studied for its use as a biosensor and in bioremediation processes. Both Aio enzymes contain a large subunit (AioA) that harbours a molybdenum centre and a [3Fe-4S] cluster, and a small subunit (AioB) that possess a Rieske [2Fe-2S] cluster and have demonstrated to oxidise AsIII, as well as SbIII, into the easier to remove and less toxic forms of AsV and SbV, respectively [3,4]. Aiming to elucidate the catalysis mechanism of the enzymes, a combination of expression and purification of the proteins, crystallisation, structural analysis, enzyme kinetics and affinity tests were conducted. X-ray structures of the ligand-free form of the enzyme had been previously determined (PDB: 4AAY, 5NQD and 1G8K [3,5,6]). In our work, Aio crystals in complex with two different forms of the substrate analogue – Sb oxyanions, with a reaction kinetic 6500 times slower than AsIII [6] – diffracted up to ca 1.8 Å resolution. The structures show the reaction intermediates bound at the active site, with a μ-oxo bridge binding Sb to the Mo atom. Analysis of bond lengths and geometry of the ligands at the Mo active site allowed us to revisit the catalytic mechanism of As oxidation [7], contributing to the understanding and future biotechnological application of this family of enzymes in water treatment.

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Allosteric hotspot in the main protease of SARS-CoV-2

PHOTO: Léonie Ströhmich

Authors: Léonie Strömich, Sophia N Yaliraki, (Imperial College London, UK)

Since the beginning of 2020 we have seen the coronavirus SARS-CoV-2 causing a global pandemic with almost 34 million cases and over 1 million deaths worldwide [as of 01.10.2020] [1.] As a result, we have seen a surge in research efforts to develop effective treatments for the underlying disease, COVID-19. One approach is to target the main protease (Mpro) of SARS-CoV-2 as it is essential for virus replication in an early step of the viral life cycle [2.] Most efforts are centred on inhibiting the orthosteric binding site of the enzyme. However, considering allosteric sites on the protein allows for more selective drug design and widens the chemical search space. Here, we report an allosteric hotspot in the SARS-CoV-2 Mpro dimer by using novel atomistic graph theoretical methods: Markov transient analyses follow the propagation of a random walker on a graph and have been shown to successfully identify allosteric communication in catalytic proteins [3.] We further score the so identified allosteric hotspots against random sites in similar distances and thus identify a statistically significant putative allosteric site in the SARS-CoV-2 Mpro. We then simulate a binding event at this hotspot region using data from a recent XChem fragment screen by the Diamond Light Source [4.] which provides a starting point for rational drug design. This study uses highly efficient network theoretical models to shed light on allosteric communication and uncovers putative allosteric sites in the SARS-CoV-2 main protease. This provides a valuable contribution to the ongoing efforts to find a cure against COVID-19 by broadening the horizon for drug discovery efforts.

Image: Léonie Ströhmich

[1.] Official World Health Organization COVID-19
dashboard: (Accessed: 01.10.2020).
[2.] Hilgenfeld, R. (2014). FEBS Journal, 281(18), 4085-4096.
[3.] Amor, B., Yaliraki, S. N., Woscholski, R., & Barahona, M. (2014) Molecular BioSystems, 10(8), 2247-2258.
[4.] Douangamath, A., Fearon, D., Gehrtz, P., Krojer, T., Lukacik, P., Owen, C. D., … Walsh, M. A. (2020) Nature Communications, 11, 5047.

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