Unusual nucleosome formation and transcriptome influence by the histone H3mm18 variant

Area of Science:

• Molecular Biology
• Genetics
• Cell Biology

Background:

• Histone H3mm18 is a non-allelic histone variant found in mouse skeletal muscle and brain.
• The specific function of Histone H3mm18 in cellular processes remains largely unknown.
• Understanding histone variants is crucial for deciphering gene regulation mechanisms.

Purpose of the Study:

• To investigate the structural and functional properties of Histone H3mm18.
• To elucidate the role of H3mm18 in chromatin structure and gene expression.
• To explore the potential impact of H3mm18 on muscle differentiation.

Main Methods:

• Cryo-electron microscopy was used to determine the structure of nucleosome core particles (NCPs) containing H3mm18.
• In vitro stability assays were performed on H3mm18 NCPs.
• Forced expression of H3mm18 in mouse myoblast C2C12 cells was utilized.
• Transcriptome analysis was conducted to assess gene expression changes.

Main Results:

• H3mm18 is incorporated into chromatin less efficiently than H3.3.
• H3mm18 NCPs exhibit disordered entry/exit DNA regions and are structurally unstable.
• Forced H3mm18 expression suppressed muscle differentiation in C2C12 cells.
• Transcriptome analysis revealed downregulation of muscle development genes upon H3mm18 overexpression.

Conclusions:

• Histone H3mm18 forms unstable nucleosomes that alter chromatin landscape.
• H3mm18 can negatively regulate gene expression, particularly genes involved in muscle development.
• This study introduces a novel gene regulation system mediated by unusual histone variant nucleosomes.