Leukodystrophy-associated POLR3A mutations down-regulate the RNA polymerase III transcript and important regulatory...

Area of Science:

• Molecular Biology
• Neuroscience
• Genetics

Background:

• RNA polymerase III (Pol III) synthesizes small noncoding RNAs crucial for mRNA translation.
• Mutations in POLR3A, encoding the largest Pol III subunit, lead to POLR3-related hypomyelinating leukodystrophy (POLR3-HLD), a disorder of deficient central nervous system myelination.
• Downstream effectors of POLR3A mutations in POLR3-HLD remain largely unidentified.

Purpose of the Study:

• To investigate the impact of a specific POLR3A mutation on Pol III function and identify downstream effectors in cellular models of POLR3-HLD.
• To assess the role of candidate effectors, such as BC200 RNA, in oligodendrocyte biology and POLR3-HLD pathogenesis.

Main Methods:

• CRISPR-Cas9 gene editing to introduce the POLR3A c.2554A→G (p.M852V) mutation into human cell lines.
• Assessment of Pol III biogenesis, nuclear import, DNA occupancy, transcription, and protein levels.
• Transcriptomic and proteomic profiling, including analysis of BC200 RNA deletion and myelin basic protein (MBP) gene expression.

Main Results:

• The POLR3A mutation impaired Pol III transcription, leading to global reduction in tRNA levels and affecting specific transcripts like BC200 RNA.
• Genomic deletion of BC200 RNA in oligodendroglial cells caused significant transcriptomic and proteomic alterations.
• POLR3A-mutant cells showed decreased mRNA levels of myelin basic protein (MBP) upon differentiation.

Conclusions:

• This study provides the first evidence of impaired Pol III transcription in cellular models of POLR3-HLD.
• BC200 RNA and MBP are identified as potential key effectors in POLR3-HLD, highlighting their roles in oligodendrocyte biology and disease development.