Fig 11. Article summary: Mitotic DNA damage response.

(A) A 780nm femtosecond laser was focused to a sub-micron region on a mitotic chromosome. End breaks detected via TUNEL assay and cyclo-butane pyrimidine dimers were found at the laser damage site. (B) Several factors clustered to the damage site. In bold are the repair pathway abbreviations that each factor is most closely associated with. Non-Homologous End Joining (NHEJ), Single Strand Break Repair (SSBR), Base Excision Repair (BER), Homologous Recombination (HR) Post translational modifications (PTM), Nucleotide excision repair (NER). DNA synthesis occurs at the damaged chromosome region as detected via EdU incorporation. Phosphorylated Histone γH2AX on Serine 139 marks double strand breaks and extends from the laser damage spot. Based on the recruitment of the corresponding proteins, we hypothesize that these repair pathways may be activated during mitosis. It should be noted that while factors involved in both early and late steps of NHEJ are readily detectable, only those involved in early step of HR were detected, suggesting that NHEJ may be entirely active while HR may be initiated but not completed during mitosis.