The BLM helicase contributes to telomere maintenance through processing of late-replicating intermediate structures.

Area of Science:

• Genetics
• Molecular Biology
• Cancer Research

Background:

• Werner syndrome (WS) and Bloom syndrome (BS) are rare genetic disorders linked to cancer predisposition.
• Both syndromes result from mutations in RecQ helicase genes (WRN for WS, BLM for BS), leading to genomic instability.
• Previous research highlighted WRN's role in telomere maintenance and genomic stability, particularly in resolving replication defects.

Purpose of the Study:

• To investigate the role of the BLM helicase in chromosome-end maintenance and telomere stability.
• To understand how BLM functions in resolving replication stress and its connection to genomic aberrations.
• To explore the independent and combined roles of WRN and BLM in maintaining telomere integrity.

Main Methods:

• Analysis of telomere defects (TDs) in BLM-deficient cells.
• Assessment of chromosomal aberrations in cells with defects in WRN and/or BLM.
• Microscopic observation of BLM localization and its recruitment to telomeres under replication stress.
• Identification and quantification of ultra-fine bridges (UFBs) originating from telomeric DNA.

Main Results:

• BLM-deficient cells exhibit a significant frequency of telomere defects, comparable to WRN-deficient cells.
• Loss of both BLM and WRN function exacerbates telomere defects and chromosomal aberrations, suggesting independent roles.
• BLM is recruited to telomeres in response to replication dysfunction and forms complexes with late-replicating intermediates (LRIs).
• A subset of ultra-fine bridges (UFBs) in anaphase originates from telomeric DNA, correlating with telomere replication defects.

Conclusions:

• The BLM helicase plays a significant role in chromosome-end maintenance, similar to WRN.
• BLM contributes to telomere maintenance by resolving late-replicating intermediates (LRIs) and resolving DNA structures that form under replication stress.
• BLM and WRN function independently but cooperatively in maintaining telomere integrity and overall genomic stability, offering insights into cancer predisposition syndromes.