Persistent DNA damage signaling and DNA polymerase theta promote broken chromosome segregation

Area of Science:

• Cellular biology
• Genetics
• Molecular biology

Background:

• DNA double-strand breaks (DSBs) pose a threat to genome stability.
• Missegregation of chromosomes with DSBs during mitosis leads to micronuclei, which are linked to diseases.
• The response of cells to DSBs during mitosis is not fully understood, especially in cells lacking DSB checkpoints.

Purpose of the Study:

• To investigate how cells with inactive DSB checkpoints respond to DNA damage that persists into mitosis.
• To identify the key molecular players involved in DSB repair during mitosis in such cells.

Main Methods:

• Utilized Drosophila melanogaster papillar cells, which lack DSB checkpoints.
• Observed the recruitment and dynamics of DNA repair proteins (Mre11, RPA3, Fancd2) at DSBs during mitosis.
• Assessed the role of Fancd2 monoubiquitination and DNA polymerase theta in DSB repair and micronuclei formation.

Main Results:

• Papillar cells recruit early repair machinery and Fanconi anemia (FA) protein Fancd2 to DSBs, forming persistent foci.
• These repair foci are resolved in a stepwise manner during mitosis.
• Fancd2 monoubiquitination and DNA polymerase theta are crucial for DSB repair kinetics.
• Disruption of these factors leads to micronuclei formation and disrupts intestinal organogenesis.

Conclusions:

• Cells with inactive DSB checkpoints possess a mechanism to respond to mitotic DNA damage.
• Fancd2 monoubiquitination and DNA polymerase theta are essential for resolving DSBs during mitosis and preventing genomic instability.
• This study reveals a novel pathway for DNA damage response in cells with compromised checkpoint function.