Identification of HMCES as the Core Genetic Determinant Underlying the xhs1 Radiosensitivity Locus in LEA/LEC Rats

Area of Science:

• Genetics
• Molecular Biology
• Radiobiology

Background:

• Genomic instability from faulty DNA double-strand break (DSB) repair dictates cellular radiosensitivity.
• The Long-Evans cinnamon (LEC) rat exhibits significant radiosensitivity, linked to the X-ray hypersensitivity 1 (xhs1) locus on chromosome 4, but its mechanism is unknown.

Purpose of the Study:

• To investigate the cellular and molecular basis of xhs1-associated radiosensitivity in LEC rats.
• To identify the specific gene and protein responsible for the observed radiosensitivity.

Main Methods:

• RNA sequencing (RNA-seq) of liver tissue to identify genetic variants.
• Analysis of HMCES protein levels in various tissues and cell lines.
• Functional assays including γH2AX signaling, clonogenic survival, and reporter assays for DNA repair mechanisms (e.g., end-joining).

Main Results:

• A sequence variant in the Hmces gene was identified in LEC rats, leading to significantly reduced HMCES protein levels.
• HMCES deficiency resulted in prolonged γH2AX signaling post-irradiation, indicating delayed DSB repair.
• HMCES-deficient cells exhibited increased radiosensitivity and impaired end-joining repair activity, which was partially rescued by HMCES re-expression.

Conclusions:

• HMCES is a crucial mediator of DNA double-strand break repair and cellular radioresistance.
• HMCES dysfunction is the genetic cause of xhs1-associated radiosensitivity in LEC rats.
• This study provides mechanistic insights into radiation response in a naturally occurring radiosensitive model.