Biology subjects

Shaban, H. A.

Publications and source records attributed to Shaban, H. A..

5 recordsLinked to original sources

bioRxiv2022

Spatially coherent diffusion of human RNA Pol II depends on transcriptional state rather than chromatin motion

Gene transcription by RNA polymerase II (RNAP II) is a tightly regulated process in the genomic, temporal, and spatial context. Transcriptionally active genes often spatially cluster at RNA Pol II foci, called transcription factories, causing long-range interactions between distal sites of the genome. Recently, we have shown that chromatin exhibits spatially long-range coherently moving regions over the entire nucleus, and transcription enhances this long-range correlated DNA movement. Yet, it remains unclear how the mobility of RNA Pol II molecules is affected by transcription regulation and whether this response depends on the coordinated chromatin movement. We applied our Dense Flow reConstruction and Correlation method to analyze nucleus-wide coherent movements of RNA Pol II in living human cancer cells. We quantify the spatial correlation length of RNA Pol II in the context of DNA motion. We observe a spatially coherent movement of RNA Pol II molecules over ~1 m, considerably less than for DNA, suggesting that spatially coherent RNA Pol II motion does not solely result from the DNA motion. In contrast to DNA, inducing transcription in quiescent cells decreased the coherent motion of RNA Pol II, while the inhibition of transcription elongation by using DRB slightly increased coherent RNA Pol II motion. The spatially coherent movement of RNA Pol II domains is affected by the transcriptional state and largely independent of the underlying chromatin domains. Our study reveals the nucleus-wide interplay between chromatin and RNA Pol II in the dynamic regulation of chromatin organization.

biophysics↗

bioRxiv2019

Chromatin arranges in filaments of blobs with nanoscale functional zonation

Three-dimensional (3D) chromatin organization plays a key role in regulating mammalian genome function, however many of its physical features at the single-cell level remain underexplored. Here we use 3D super-resolution and scanning electron microscopy to analyze structural and functional nuclear organization in somatic cells. We identify linked chromatin domains (CDs) composed of irregular [~]200-300-nm-wide aggregates of nucleosomes that can overlap with individual topologically associating domains and are distinct from a surrounding RNA-populated interchromatin region. High-content mapping uncovers confinement of cohesin and active histone modifications to surfaces and enrichment of repressive modifications towards the core of CDs in both hetero- and euchromatic regions. This nanoscale functional topography is temporarily relaxed in post-replicative chromatin, but remarkably persists after ablation of cohesin. Our findings establish CDs as physical and functional modules of mesoscale genome organization.

genomics↗

bioRxiv2018

Nanoscale mapping of DNA dynamics reveals activity-driven genome organization in living human cells

Bulk chromatin motion has not been analysed at high resolution. We present Hi-D, a method to quantitatively map dynamics of chromatin and abundant nuclear proteins for every pixel simultaneously over the entire nucleus from fluorescence image series. Hi-D combines reconstruction of chromatin motion, and classification of local diffusion processes by Bayesian inference. We show that DNA dynamics in the nuclear interior are spatially partitioned into 0.3 - 3 m domains in a mosaic-like pattern, uncoupled from chromatin compaction. This pattern was remodelled in response to transcriptional activity. Hi-D can be applied to any dense and bulk structures opening new perspectives towards understanding motion of nuclear molecules.

biophysics↗

bioRxiv2017

Formation of correlated chromatin domains at nanoscale dynamic resolution during transcription

Intrinsic dynamics of chromatin contribute to gene regulation. How chromatin mobility responds to genomic processes and whether this response relies on coordinated movement is still unclear. Here, we introduce an approach called Dense Flow reConstruction and Correlation (DFCC) to quantify correlation of chromatin motion with sub-pixel sensitivity at the level of the whole nucleus. DFCC is based on reconstructing dense global flow fields of fluorescent images acquired in real-time. By simulating variations in microscopic and dynamic parameters, we demonstrate that our approach is robust and more accurate than other methods to estimate flow fields and spatial correlations of dense structures such as chromatin. We applied our approach to analyze stochastic movements of DNA and histones based on direction and magnitude at different time lags in human cells. We observe long-range correlations extending over several m between coherently moving regions over the entire nucleus. Spatial correlation of global chromatin dynamics was reduced by inhibiting elongation by RNA polymerase II and abolished in quiescent cells. Furthermore, quantification of spatial smoothness over time intervals up to 30 seconds points to clear-cut boundaries between distinct regions, while smooth transitions in small (<1 m) neighborhoods dominate for short time intervals. Clear transitions between regions of coherent motion indicate directed squeezing or stretching of chromatin boundaries suggestive of changes in local concentrations of actors regulating gene expression. The DFCC approach hence allows characterizing stochastically forming domains of specific nuclear activity.\n\nSignificance StatementControl of gene expression relies on modifications of chromatin structure and activity of the transcription machinery. However, how chromatin responds dynamically to this genomic process and whether this response is coordinated in space is still unclear. We introduce a novel approach called Dense Flow reConstruction and Correlation (DFCC) to characterize spatially correlated dynamics of chromatin in living cells at nanoscale resolution. DFCC allows us to detect chromatin domains in living cells with long range correlations over the entire nucleus. Furthermore, transitions between domains can be quantified by the newly introduced smoothness parameter of local chromatin motion. The DFCC approach permits characterizing stochastically forming domains of other DNA dependent activity in any cell type in real time imaging.

biophysics↗

bioRxiv2017

Real-time chromatin dynamics at the single gene levelduring transcription activation

Genome dynamics relate to regulation of gene expression, the most fundamental process in biology. Yet we still do not know whether the very process of transcription drives spatial organization and chromatin conformation at specific gene loci. To address this issue, we have optimized the ANCHOR/ParB DNA labeling system for real-time imaging and quantitative analysis of the dynamics of a single-copy transgene in human cells. Transcription of the transgene under the control of the endogenous Cyclin D1 promoter was induced by addition of 17{beta}-estradiol. Motion of the ANCHOR3-tagged DNA locus was recorded in the same cell prior to and during appearance of nascent mRNA visualized using the MS2 system. We found that transcription initiation resulted in rapid confinement of the mRNA-producing gene. The confinement was maintained even upon inhibition of pol2 elongation. It did not occur when recruitment of pol2 or transcription initiation was blocked by anti-estrogens or Triptolide. These results suggest that preinitiation complex formation and concomitant reorganization of the chromatin domain constrains freedom of movement of an induced genes promoter within minutes. Confined diffusion reflects assembly of functional protein hubs and DNA processing during the rate-limiting steps of transcription.

cell biology↗