BRCA1 prevents R-loop-associated centromeric instability

Area of Science:

• Molecular Biology
• Genetics
• Cell Biology

Background:

• Centromeres are crucial for chromosome inheritance, defined by CENP-A chromatin on α-satellite DNA, which is transcribed throughout the cell cycle.
• BRCA1 (Breast Cancer gene 1) is a tumor suppressor known to associate with centromeric chromatin, but its recruitment mechanism and centromeric function were unclear.

Purpose of the Study:

• To elucidate the mechanism of BRCA1 recruitment to centromeres and its role in maintaining centromere stability.
• To investigate the functional relationship between BRCA1, R-loops, and centromeric chromatin.

Main Methods:

• Assessed BRCA1 association with centromeric chromatin in relation to R-loop presence.
• Studied the effects of BRCA1 deficiency on CENP-A localization, centromeric transcription, and DNA damage.
• Investigated R-loop dependency of observed phenotypes.
• Analyzed Rad52-dependent recombination in BRCA1-depleted cells.

Main Results:

• BRCA1 recruitment to centromeres is dependent on the presence of R-loops (DNA:RNA hybrids).
• BRCA1 counteracts R-loop accumulation at centromeric α-satellite repeats.
• BRCA1-deficient cells exhibit impaired CENP-A localization, increased centromeric transcription, DNA breakage, and micronuclei formation, all dependent on R-loops.
• BRCA1 depletion leads to Rad52-dependent hyper-recombination at centromeric repeats, causing instability and missegregation.

Conclusions:

• BRCA1 plays a critical role in maintaining centromere stability and identity by resolving R-loops.
• The findings reveal a novel mechanism for BRCA1's tumor suppressor function at centromeres, linking R-loop resolution to genome stability.