Y265C DNA polymerase beta knockin mice survive past birth and accumulate base excision repair intermediate substrates

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• DNA damage is a constant threat to genomic integrity, necessitating robust repair mechanisms.
• DNA polymerase beta (pol β) is a critical enzyme in the base excision repair (BER) pathway.
• Complete absence of pol β in mice leads to embryonic lethality shortly after birth.

Purpose of the Study:

• To investigate the in vivo consequences of a specific impaired DNA polymerase beta (Y265C) variant.
• To determine the essentiality of pol β's polymerase activity versus its lyase activity for organismal survival and genome stability.

Main Methods:

• Characterization of mice engineered to express a Y265C pol β variant with reduced polymerase but normal lyase activity.
• Analysis of embryonic development, survival rates, and cell proliferation in homozygous Y265C mutant mice and their wild-type littermates.
• Assessment of DNA repair efficiency, chromosomal aberrations, and DNA strand breaks in mouse embryo fibroblasts (MEFs) from mutant embryos.

Main Results:

• Mice expressing the Y265C pol β variant were viable at birth but exhibited reduced size and high postnatal mortality (60%).
• Homozygous mutant embryos displayed slower proliferation and increased cell death in multiple organs.
• Y265C mutant MEFs showed impaired gap-filling during BER, leading to significantly elevated chromosomal aberrations and DNA strand breaks.

Conclusions:

• The DNA polymerase activity of pol β, but not its lyase activity, is essential for embryonic development, survival, and maintaining genome stability.
• Separating the enzymatic activities of pol β provides critical insights into its distinct roles in DNA repair.
• This study highlights the indispensable function of pol β's polymerase function in preventing genotoxicity and ensuring organismal viability.