Dynamic nucleosome remodeling mediated by YY1 underlies early mouse development.

Area of Science:

• Epigenetics and Developmental Biology
• Chromatin Structure and Dynamics
• Mammalian Embryogenesis

Background:

• Nucleosome positioning is critical for regulating DNA accessibility and gene expression, influencing cell identity.
• Early mammalian development involves dynamic gene expression and cell potency changes, implying epigenetic regulation.
• The precise dynamics of nucleosome organization during preimplantation development remain largely uncharacterized.

Purpose of the Study:

• To investigate the dynamics of nucleosome organization during early mouse embryonic development.
• To identify the mechanisms underlying the observed changes in nucleosome positioning.
• To understand the role of specific factors, like YY1, in establishing chromatin structure during development.

Main Methods:

• Utilized a low-input Micrococcal Nuclease sequencing (MNase-seq) method to profile nucleosome positioning.
• Investigated the effect of chromatin assembly on nucleosome organization by down-regulating components in embryonic stem cells.
• Identified transcription factor binding sites (YY1) in eight-cell embryos and analyzed associated epigenetic modifications.

Main Results:

• Nucleosome positioning was globally obscure in zygotes and became well-defined in later embryonic stages.
• Down-regulation of chromatin assembly factors partially restored a zygote-like nucleosome pattern.
• Transcription factor YY1 was identified as a key regulator of de novo nucleosome array formation at regulatory elements.
• YY1-bound regions showed H3K27ac enrichment, and YY1 depletion disrupted the morula-to-blastocyst transition.

Conclusions:

• Nucleosome organization undergoes significant remodeling during early mouse development, transitioning from a 'fuzzy' state to a defined state.
• Chromatin assembly pathways and the transcription factor YY1 are crucial for establishing well-positioned nucleosomes during embryogenesis.
• YY1 plays a critical role in regulating gene accessibility and developmental progression through its influence on nucleosome organization.