Disruption of murine Mus81 increases genomic instability and DNA damage sensitivity but does not promote tumorigenesis.

in Molecular and cellular biology by Najoua Dendouga, Hui Gao, Dieder Moechars, Michel Janicot, Jorge Vialard, Clare H McGowan

TLDR

  • The study looked at how a protein called Mus81-Eme1 helps fix broken parts of DNA in yeast and a type of worm called Schizosaccharomyces pombe. They used gene targeting to study the function of this protein in mammalian cells (like human cells). They found that Mus81-deficient mice develop normally and are fertile, but embryonic fibroblasts from Mus81(-/-) animals fail to proliferate in vitro. This means that the protein is not essential for mammalian replication and DNA repair, but it plays a critical role in the resolution of cross-link-induced lesions. Despite these defects, Mus81(-/-) mice do not show increased predisposition to lymphoma or any other malignancy in the first year of life. The study highlights the importance of understanding the role of endonucleases in DNA repair and their potential as therapeutic targets for cancer treatment.

Abstract

The Mus81-Eme1 endonuclease is implicated in the efficient rescue of broken replication forks in Saccharomyces cerevisiae and Schizosaccharomyces pombe. We have used gene targeting to study the function of the Mus81-Eme1 endonuclease in mammalian cells. Mus81-deficient mice develop normally and are fertile. Surprisingly, embryonic fibroblasts from Mus81(-/-) animals fail to proliferate in vitro. This proliferation defect can be rescued by expression of the papillomavirus E6 protein that promotes degradation of p53. When grown in culture, Mus81(-/-) cells have elevated levels of DNA damage, acquire chromosomal aberrations, and are hypersensitive to agents that generate DNA cross-links. In contrast to the situation in yeast, murine Mus81 is not required for replication restart following camptothecin treatment. Mus81(-/-) mice and cells are hypersensitive to DNA cross-linking agents. Cross-link-induced double-strand break formation is normal in Mus81(-/-) cells, but the resolution of repair intermediates is not. The persistence of Rad51 foci in Mus81(-/-) cells suggests that Mus81 acts at a late step in the repair of cross-link-induced lesions. Despite these defects, Mus81(-/-) mice do not show increased predisposition to lymphoma or any other malignancy in the first year of life.

Overview

  • The study investigates the function of the Mus81-Eme1 endonuclease in mammalian cells using gene targeting. The hypothesis being tested is whether Mus81-Eme1 is required for efficient rescue of broken replication forks in mammalian cells. The methodology used includes gene targeting, in vitro proliferation assays, and DNA damage and sensitivity tests. The primary objective of the study is to understand the role of Mus81-Eme1 in mammalian replication and DNA repair.

Comparative Analysis & Findings

  • The study found that Mus81-deficient mice develop normally and are fertile, but embryonic fibroblasts from Mus81(-/-) animals fail to proliferate in vitro. This proliferation defect can be rescued by expression of the papillomavirus E6 protein. Mus81(-/-) cells have elevated levels of DNA damage, acquire chromosomal aberrations, and are hypersensitive to agents that generate DNA cross-links. In contrast to yeast, murine Mus81 is not required for replication restart following camptothecin treatment. Cross-link-induced double-strand break formation is normal in Mus81(-/-) cells, but the resolution of repair intermediates is not. The persistence of Rad51 foci in Mus81(-/-) cells suggests that Mus81 acts at a late step in the repair of cross-link-induced lesions. Despite these defects, Mus81(-/-) mice do not show increased predisposition to lymphoma or any other malignancy in the first year of life.

Implications and Future Directions

  • The study's findings suggest that Mus81-Eme1 is not essential for mammalian replication and DNA repair, but it plays a critical role in the resolution of cross-link-induced lesions. Future research could explore the mechanisms underlying the persistence of Rad51 foci in Mus81(-/-) cells and the role of Mus81 in the repair of other types of DNA damage. The study also highlights the importance of understanding the role of endonucleases in DNA repair and their potential as therapeutic targets for cancer treatment.
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