New Face for Chromatin-Related Mesenchymal Modulator: n-CHD9 Localizes to Nucleoli and Interacts With Ribosomal Genes

Area of Science:

• Epigenetics
• Molecular Biology
• Cell Biology

Background:

• Mesenchymal stem cell differentiation involves transcription factors regulating gene promoters.
• Chromatin-Related Mesenchymal Modulator (CHD9) remodels nucleosomes and interacts with RNA Polymerase II (Pol II).
• The role of CHD9 in RNA Polymerase I (Pol I) transcription, particularly of the ribosomal locus, is largely unknown.

Purpose of the Study:

• To investigate the function of CHD9 in RNA Polymerase I (Pol I) transcription and ribosomal DNA (rDNA) biogenesis.
• To characterize a newly identified nucleolar form of CHD9 (n-CHD9).

Main Methods:

• Imaging and molecular approaches to detect n-CHD9 localization and interactions.
• Chromatin immunoprecipitation (ChIP) and tiling arrays (ChIP-chip) to assess n-CHD9 association with rDNA genes.
• Inhibition of transcription to observe effects on nucleolar structure.

Main Results:

• A novel nucleolar form, n-CHD9, was identified and shown to associate dynamically with Pol I, fibrillarin, and upstream binding factor (UBF) in nucleoli.
• Transcription inhibition disrupted the nucleolar compartment of active rDNA transcription sites.
• ChIP-chip analysis revealed n-CHD9 association with Pol I at rDNA genes, indicating a role in rRNA biogenesis.

Conclusions:

• n-CHD9 is linked to RNA Pol I transcription within the fibrillar centers of the nucleolus.
• CHD9 plays a role in chromatin regulation and association with rDNA genes, extending its known function in tissue-specific gene transcription.