Embryonic genome instability upon DNA replication timing program emergence

Area of Science:

• Developmental Biology
• Genetics
• Molecular Biology

Background:

• Faithful DNA replication is crucial for maintaining genome integrity.
• Replication defects and chromosome segregation errors are observed in early embryogenesis.
• Regulation of DNA replication in early mammalian embryos is not well understood.

Purpose of the Study:

• To investigate the DNA replication program in pre-implantation mouse embryos at a single-cell level.
• To identify critical periods of genomic instability during early development.
• To understand the coordination between replication timing and fork progression.

Main Methods:

• Construction of a single-cell, genome-wide DNA replication atlas in mouse embryos.
• Analysis of replication timing programs and replication fork speeds.
• Assessment of replication stress, DNA damage, and chromosome segregation errors.

Main Results:

• Early embryos (1-2 cell) lack a replication timing program with slow, uniform replication.
• A somatic-like replication program initiates by the 4-cell stage, but with slow forks and increased replication stress.
• Break-type chromosome segregation errors occur during the 4-to-8 cell division, linked to late-replicating regions.
• Nucleoside supplementation rescues errors by accelerating fork speed and reducing stress.
• By the 8-cell stage, replication dynamics normalize, and chromosome aberrations decrease.

Conclusions:

• A transient period of genomic instability occurs during normal mouse development.
• This instability is linked to a lack of coordination between replication timing and fork regulation in early S phase.
• Coordination of replication processes is vital for maintaining genome stability during embryogenesis.