Biology subjects

Karpinska, M.

Publications and source records attributed to Karpinska, M..

4 recordsLinked to original sources

bioRxiv2026

Analysis of multi-way chromatin interactions at sub-nucleosome resolution identifies synergistic nano-scale interactions within super-enhancers

In-depth understanding of the 3D organization of the genome and its role in the regulation of gene expression requires techniques to measure complex chromosome conformations at single alleles at high resolution. Here, we present multi-way Micro-Capture-C (mwMCC), a method to detect concurrent interactions between multiple chromatin regions at single alleles at sub-nucleosome resolution. mwMCC resolves the internal 3D structure of super-enhancers and identifies synergistic multi-way interactions between their constituent elements and gene promoters, providing a structural basis for cooperation within super-enhancers in nano-scale chromatin hubs. The dynamic formation and dissolution of these hubs during cellular differentiation correlates with up- and down-regulation of gene expression. Although large-scale chromatin hubs are dependent on the architectural protein CTCF, nano-scale hubs are robust to CTCF depletion. Instead, integration of footprinting analysis and protein occupancy data indicates a role for transcription factors and the co-activator Mediator in the formation of synergistic enhancer-promoter interactions within nano-scale chromatin hubs.

genomics↗

bioRxiv2024

The estrous cycle modulates hippocampal spine dynamics, dendritic processing, and spatial coding

AbstractHistological evidence suggests that the estrous cycle exerts a powerful effect on CA1 neurons in mammalian hippocampus. Decades have passed since this landmark observation, yet how the estrous cycle shapes dendritic spine dynamics and hippocampal spatial coding in vivo remains a mystery. Here, we used a custom hippocampal microperiscope and two-photon calcium imaging to track CA1 pyramidal neurons in female mice over multiple cycles. Estrous cycle stage had a potent effect on spine dynamics, with heightened density during periods of greater estradiol (proestrus). These morphological changes were accompanied by greater somatodendritic coupling and increased infiltration of back-propagating action potentials into the apical dendrite. Finally, tracking CA1 response properties during navigation revealed enhanced place field stability during proestrus, evident at the single-cell and population level. These results establish the estrous cycle as a driver of large-scale structural and functional plasticity in hippocampal circuits essential for learning and memory.

neuroscience↗

bioRxiv2023

G-quadruplexes are promoter elements controlling nucleosome exclusion and RNA polymerase II pausing

Despite their central role in transcription, it has been difficult to define universal sequences associated to eukaryotic promoters. Within chromatin context, recruitment of the transcriptional machinery requires opening of the promoter but how DNA elements could contribute to this process has remained elusive. Here, we show that G-quadruplex (G4) secondary structures are highly enriched mammalian core promoter elements. G4s are located at the deepest point of nucleosome exclusion at promoters and correlate with maximum promoter activity. We found that experimental G4s exclude nucleosomes both in vivo and in vitro and display a strong positioning potential. At model promoters, impairing G4s affected both transcriptional activity and chromatin opening. G4 destabilization also resulted in an inactive promoter state and affected transition to effective RNA production in live imaging experiments. Finally, G4 stabilization resulted in global reduction of proximal promoter pausing. Altogether, our data introduce G4s as bona fide promoter elements allowing nucleosome exclusion and facilitating pause release by the RNA Polymerase II.

genomics↗

bioRxiv2022

The Mediator complex regulates enhancer-promoter interactions

Enhancer-mediated gene activation generally requires physical proximity between enhancers and their target gene promoters. However, the molecular mechanisms by which interactions between enhancers and promoters are formed are not well understood. Here, we investigate the function of the Mediator complex in the regulation of enhancer-promoter interactions, by combining rapid protein depletion and high-resolution MNase-based chromosome conformation capture approaches. We show that depletion of Mediator leads to reduced enhancer-promoter interaction frequencies, which are associated with a strong decrease in gene expression. In addition, we find increased interactions between CTCF-binding sites upon Mediator depletion. These changes in chromatin architecture are associated with a re-distribution of the Cohesin complex on chromatin and a reduction in Cohesin occupancy specifically at enhancers. Our results indicate that enhancer-promoter interactions are dependent on an interplay between the Mediator and Cohesin complexes and provide new insights into the molecular mechanisms by which communication between enhancers and promoters is regulated.

molecular biology↗