Biology subjects

Oravecz, A.

Publications and source records attributed to Oravecz, A..

4 recordsLinked to original sources

bioRxiv2025

RNA polymerase II initiation factors show different dynamic behaviour upon induced transcription in live cells

Transcription by RNA polymerase II (Pol II) requires the ordered action of general transcription factors (GTFs) forming the pre-initiation complex (PIC). How these events unfold kinetically remains unclear. Upon transcription activation, we observe coordinated recruitment of Pol II and GTFs together with chromatin decompaction. Pol II and its Ser5-phosphorylated form accumulate and persist at promoters, whereas TFIIB and TFIIF engage transiently, revealing distinct dynamic regimes. We find specific residence kinetics consistent with rapid exchange of GTFs and a more stable initiating Pol II population. A quantitative kinetic model recapitulates the temporal ordering and relative amplitudes of factor recruitment, predicts recruitment times, and links transient GTF engagement to sustained Pol II occupancy. Steady state measurements and transcription inhibition corroborate model predictions. These results uncover a dynamic hierarchy in human PIC assembly and establish a quantitative framework that connects factor exchange kinetics to the regulation of Pol II activity in living cells.

molecular biology↗

bioRxiv2024

Piggybacking functionalized DNA nanostructures into live cell nuclei

DNA origami (DO) are promising tools for in vitro or in vivo applications including drug delivery; biosensing, detecting biomolecules; and probing chromatin sub-structures. Targeting these nanodevices to mammalian cell nuclei could provide impactful approaches for probing visualizing and controlling important biological processes in live cells. Here we present an approach to deliver DO strucures into live cell nuclei. We show that labelled DOs do not undergo detectable structural degradation in cell culture media or human cell extracts for 24 hr. To deliver DO platforms into the nuclei of human U2OS cells, we conjugated 30 nm long DO nanorods with an antibody raised against the largest subunit of RNA Polymerase II (Pol II), a key enzyme involved in gene transcription. We find that DOs remain structurally intact in cells for 24hr, including within the nucleus. Using fluorescence microscopy we demonstrate that the electroporated anti-Pol II antibody conjugated DOs are efficiently piggybacked into nuclei and exihibit sub-diffusive motion inside the nucleus. Our results reveal that functionalizing DOs with an antibody raised against a nuclear factor is a highly effective method for the delivery of nanodevices into live cell nuclei.

bioengineering↗

bioRxiv2021

Cell cycle gene regulation dynamics revealed by RNA velocity and deep-learning

The cell cycle is a fundamental process of life, however, a quantitative understanding of gene regulation dynamics in the context of the cell cycle is still far from complete. Single-cell RNA-sequencing (scRNA-seq) technology gives access to its dynamics without externally perturbing the cell. Here, we build a high-resolution map of the cell cycle transcriptome based on scRNA-seq and deep-learning. By generating scRNA-seq libraries with high depth, in mouse embryonic stem cells and human fibroblasts, we are able to observe cycling patterns in the unspliced-spliced RNA space for single genes. Since existing methods in scRNA-seq are not efficient to measure cycling gene dynamics, we propose a deep learning approach to fit these cycling patterns sorting single cells across the cell cycle. We characterize the cell cycle in asynchronous pluripotent and differentiated cells identifying major waves of transcription during the G1 phase and systematically study the G1-G0 transition where the cells exit the cycle. Our work presents to the scientific community a broader understanding of RNA velocity and cell cycle maps, that we applied to pluripotency and differentiation. Our approach will facilitate the study of the cell cycle in multiple cellular models and different biological contexts, such as cancer and development.

systems biology↗

bioRxiv2021

Precise measurements of chromatin diffusion dynamics by modeling using Gaussian processes

The spatiotemporal organization of chromatin influences many nuclear processes: from chromo-some segregation to transcriptional regulation. To get a deeper understanding of these processes it is essential to go beyond static viewpoints of chromosome structures, and to accurately characterize chromatin mobility and its diffusion properties. Here, we present GP-FBM: a new computational framework based on Gaussian processes and fractional Brownian motion to analyze and extract diffusion properties from stochastic trajectories of labeled chromatin loci. GP-FBM is able to optimally use the higher-order correlations present in the data and therefore outperforms existing methods. Furthermore, GP-FBM is able to extrapolate trajectories from missing data and account for substrate movement automatically. Using our method we show that diffusive chromatin diffusion properties are surprisingly similar in interphase and mitosis in mouse embryonic stem cells. Moreover, we observe surprising heterogeneity in local chromatin dynamics, which correlates with transcriptional activity. We also present GP-Tool, a user-friendly graphical interface to facilitate the use of GP-FBM by the research community for future studies of nuclear dynamics.

systems biology↗