Immunocytochemical Localization of XRCC1 and γH2AX Foci Induced by Tightly Focused Femtosecond Laser Radiation in Cultured Human Cells

Specificity of DNA damage formation induced by femtosecond near-infrared laser filamentation in water

We investigated the deoxyribonucleic acid (DNA) damage induced by laser filamentation, which was generated by focusing femtosecond near-infrared Ti:Sapphire laser light in water at several repetition rates ranging from 1000 Hz to 10 Hz. Using plasmid DNA (pUC19), the single-strand break, double-strand break, nucleobase lesions, and the fragmented DNA were analyzed and quantified by agarose gel electrophoresis. Additionally, the H2O2 concentration after irradiation was determined. We observed that (1) the DNA damage per laser shot and (2) the enzyme-sensitive base lesions per total DNA damage decreased as the laser repetition rate increased. Furthermore, (3) extraordinarily short DNA fragments were likely to be produced, compared with those produced using X-rays, and (4) most OH radicals could be eliminated by recombination to generate H2O2, preventing them from damaging the DNA. The Monte-Carlo simulation of the strand break formation implies that the observed dependency of strand break efficiency on the laser repetition rate is mainly due to diffusion of DNA molecules. These findings quantitatively and qualitatively revealed that an intense laser pulse induces a specific DNA damage profile that is not induced by X-rays, a sparsely ionizing radiation source.

Stain-free enucleation of mouse and human oocytes with a 1033 nm femtosecond laser

Significance

Preparation of a recipient cytoplast by oocyte enucleation is an essential task for animal cloning and assisted reproductive technologies in humans. The femtosecond laser is a precise and low-invasive tool for oocyte enucleation, and it should be an appropriate alternative to traditional enucleation by a microneedle aspiration. However, until recently, the laser enucleation was performed only with applying a fluorescent dye.

Aim

This work is aimed to (1) achieve femtosecond laser oocyte enucleation without applying a fluorescent dye and (2) to study the effect of laser destruction of chromosomes on the structure and dynamics of the spindle.

Approach

We applied polarized light microscopy for spindle visualization and performed stain-free mouse and human oocyte enucleation with a 1033 nm femtosecond laser. Also, we studied transformation of a spindle after metaphase plate elimination by a confocal microscopy.

Results

We demonstrated a fundamental possibility of inactivating the metaphase plate in mouse and human oocytes by 1033 nm femtosecond laser radiation without applying a fluorescent dye. Irradiation of the spindle area, visualized by polarized light microscopy, resulted in partly or complete metaphase plate destruction but avoided the microtubules impairment. After the metaphase plate elimination, the spindle reorganized, however, it was not a complete depolymerization.

Conclusions

This method of recipient cytoplast preparation is expected to be useful for animal cloning and assisted reproductive technologies.

Tightly Focused Femtosecond Laser Radiation Induces DNA Double-Strand Breaks in Human Tumor Cells

We studied the formation of double-strand DNA breaks (DNA DSB) induced by femtosecond laser radiation in A549 human lung adenocarcinoma cells using immunocytochemical staining of the resulting tracks of a specific DSB marker protein phosphorylated ATM kinase (phospho-ATM). Additionally, colocalization of phospho-ATM tracks with γH2AX protein tracks was studied. The results of immunocytochemical analysis showed that 30 min after irradiation of cells with femtosecond pulses with energies of 1 and 2 nJ (radiation power density 2×10¹¹ and 4×10¹¹ W×cm^-2, respectively), the formation of tracks consisting of phospho-ATM and γH2AX proteins located in sites where the laser beam passes through the cell nuclei was observed. The presence of phospho-ATM tracks co-localized with γH2AX allows us to conclude that exposure to focused femtosecond infrared laser radiation with a pulse energy of 1-2 nJ leads to the formation of DNA DSB in irradiated cells.