Phenotype-based identification of mouse chromosome instability mutants

Area of Science:

• Genetics
• Molecular Biology
• Cancer Research

Background:

• Defects in DNA double-strand-break (DSB) repair are linked to chromosome instability and cancer development.
• Identifying novel genes involved in DSB repair is crucial for understanding cancer susceptibility.

Purpose of the Study:

• To identify novel mouse genes involved in DNA double-strand-break repair using a forward genetic screen.
• To investigate the role of DNA polymerase theta (Polq) in maintaining genomic stability.

Main Methods:

• Phenotype-driven mutagenesis screen in mice using a flow cytometric peripheral blood micronucleus assay to detect chromosome instability.
• Genetic mapping of the identified mutation (chaos1) to a specific chromosomal region.
• Sequencing of candidate genes within the mapped interval, including Polq.

Main Results:

• A recessive mutation, chaos1, was identified, causing elevated spontaneous and induced micronuclei levels, indicating chromosome damage.
• The chaos1 mutation was mapped to a 1.3-Mb interval on chromosome 16, containing the Polq gene.
• A nonconservative mutation in the ENU-induced Polq allele strongly implicates it as the cause of chaos1.
• Polq is homologous to Drosophila MUS308, involved in DNA interstrand crosslink repair and possessing helicase and polymerase domains.

Conclusions:

• The study identified a novel mouse mutant (chaos1) with defects in DNA double-strand-break repair, linked to chromosome instability.
• DNA polymerase theta (Polq) is a strong candidate gene for the chaos1 mutation, highlighting its role in maintaining genomic integrity.
• This research provides a valuable forward genetic approach for discovering new cancer susceptibility genes using chromosome instability as a biomarker.