Gene-specific factors determine mitotic expression and bookmarking via alternate regulatory elements

Area of Science:

• Molecular Biology
• Epigenetics
• Cell Biology

Background:

• Transcriptional silencing during mitosis is a key regulatory process.
• Gene expression patterns are inherited through cell division via bookmarking mechanisms.
• Major histocompatibility class II (MHCII) gene expression regulation during mitosis is not fully understood.

Purpose of the Study:

• To investigate the mitotic and post-mitotic expression of the DRA major histocompatibility class II (MHCII) gene.
• To elucidate the mechanisms of transcriptional regulation and chromatin accessibility during mitosis in different cell types.
• To identify novel roles for regulatory elements in mitotic bookmarking.

Main Methods:

• Analysis of DRA MHCII gene expression in B lymphoblastoid and epithelial cells during mitosis.
• Chromatin immunoprecipitation to assess protein occupancy at the DRA MHCII promoter and enhancer regions.
• Investigation of transcription factor and phosphatase recruitment during mitosis.

Main Results:

• Constitutively MHCII-expressing B lymphoblastoid cells maintained proximal promoter occupancy by transcription factors during mitosis.
• Mitotic epithelial cells, regardless of MHCII activity, showed depletion of proximal promoter factors.
• A distal enhancer in epithelial cells selectively recruited PP2A phosphatase via NFY, maintaining chromatin accessibility.

Conclusions:

• A distal enhancer plays a critical role in maintaining chromatin accessibility during mitosis in epithelial cells.
• This enhancer exhibits a novel anti-condensation function, contributing to mitotic bookmarking.
• The findings provide insights into the timing of post-mitotic transcriptional reactivation of the DRA MHCII gene.