Widespread changes in nucleosome accessibility without changes in nucleosome occupancy during a rapid transcriptional...

Area of Science:

• Molecular Biology
• Epigenetics
• Gene Regulation

Background:

• Transcriptional activation necessitates chromatin remodeling to enhance DNA accessibility.
• Nucleosome removal from regulatory regions is a proposed mechanism for transcriptional activation.
• The unfolded protein response (UPR) is a critical cellular pathway involving rapid gene expression changes.

Purpose of the Study:

• To investigate changes in nucleosome occupancy and accessibility during UPR-mediated transcriptional activation.
• To determine whether nucleosome removal or altered accessibility is the primary mechanism for gene activation in the UPR.

Main Methods:

• Utilized micrococcal nuclease (MNase) digestion to assess nucleosome accessibility.
• Employed ATAC-seq (assay for transposase-accessible chromatin using sequencing) to map accessible chromatin regions.
• Analyzed changes in nucleosome occupancy across promoters, gene bodies, and enhancers of UPR-activated genes.

Main Results:

• Observed no significant decrease in nucleosome occupancy on most promoters, gene bodies, and enhancers during UPR.
• Demonstrated an increase in nucleosome accessibility, independent of nucleosome removal, using MNase and ATAC-seq data.
• Found that altered nucleosome accessibility is a predominant feature during rapid transcriptional induction in the UPR.

Conclusions:

• Changes in nucleosome accessibility, rather than occupancy, are the primary drivers of transcriptional activation during the UPR.
• The study refines the understanding of chromatin dynamics in rapid gene regulation.
• Findings highlight the importance of nucleosome dynamics in cellular stress responses.