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