Dissecting gene activation and chromatin remodeling dynamics in single human cells undergoing reprogramming

Area of Science:

• Cell Biology
• Epigenetics
• Genomics

Background:

• Cell fate transitions involve complex molecular remodeling.
• Understanding the temporal dynamics of these changes at a single-cell level is challenging.
• Heterokaryon-mediated reprogramming offers a model to study early pluripotency conversion.

Purpose of the Study:

• To dissect the temporal dynamics of chromatin and gene expression changes during early pluripotency conversion.
• To investigate the cause-effect relationship between chromatin remodeling and gene activation in single cells.
• To utilize super-resolution imaging in a heterokaryon system to observe these events.

Main Methods:

• Heterokaryon-mediated reprogramming as a single-cell model.
• Super-resolution imaging to visualize molecular events.
• Analysis of histone modifications (H3K9me3, H3K27me3, H3K4me3, H3K9ac) and gene transcription (OCT4, NANOG).

Main Results:

• Somatic nuclei globally decompact chromatin and lose repressive histone marks (H3K9me3, H3K27me3) post-fusion.
• OCT4 (POU5F1) transcription begins within 24 hours without initial locus opening.
• NANOG transcription initiates at 48 hours, preceded by early genomic reopening at its locus.
• Active histone marks are not immediately acquired during early reprogramming stages.

Conclusions:

• The temporal relationship between chromatin changes and gene activation is gene-specific during reprogramming.
• Early chromatin decompaction does not always precede gene activation.
• Cellular reprogramming involves distinct temporal programs for different pluripotency genes.