Sexually dimorphic DNA damage responses and mutation avoidance in the mouse germline

Area of Science:

• Developmental Biology
• Genetics
• Molecular Biology

Background:

• Mammalian germline integrity is crucial for reproduction.
• Primordial germ cells (PGCs) are foundational to the germline but their response to DNA damage is poorly understood.
• The germline's resistance to mutation accumulation suggests robust protective mechanisms.

Purpose of the Study:

• To investigate the DNA damage response (DDR) in primordial germ cells (PGCs) following exposure to ionizing radiation (IR).
• To characterize sex-specific differences in PGCs' response to DNA damage.
• To understand the long-term consequences of DNA damage on germline development and mutation incidence.

Main Methods:

• Exposure of pregnant mice to ionizing radiation (IR) at specific gestational stages.
• Assessment of DNA damage response (DDR) in primordial germ cells (PGCs).
• Whole-genome single-cell DNA sequencing of germ cells, including DNA repair-deficient mutants (e.g., Fancm).

Main Results:

• PGCs lack a G1 cell cycle checkpoint before sex determination.
• Post-sex determination, female PGCs show uncoupled differentiation and meiosis initiation after IR.
• Male PGCs exhibit repressed piRNA metabolism and transposon derepression upon IR exposure.
• Genetic rescue of DNA repair-deficient germ cells increases mutation incidence and biases.

Conclusions:

• PGCs exhibit distinct, sex-specific DNA damage responses that can lead to developmental defects.
• Ionizing radiation exposure impacts germ cell differentiation, meiotic initiation, and epigenetic regulation.
• The study highlights a selective process favoring genetically fit PGCs for establishing the adult germline.