Consequences of the bleed-through phenomenon in immunofluorescence of proteins forming radiation-induced nuclear foci

Purpose: By allowing the visualization of the proteins inside cells, the immunofluorescence technique has revolutionized our view of events that follow radiation response. Particularly, the formation of nuclear foci, their kinetic of appearance and disappearance, and the association-dissociation of protein partners are useful endpoints to better understand the effects of ionizing radiation. Recently, the technique based on the phosphorylation of the histone 2A family, member X (H2AX) has generated a plethora of reports concerning the interaction between the major proteins involved in DNA repair and stress signaling pathways. However, some unavoidable overlaps of excitation and emission wavelength spectra (the so-called bleed-through phenomenon) of the available fluorescent markers are still generating discrepancies and misinterpretations in the choreographyof DNA damage response. Biases are particularly strong with the fluorescein isothiocyanate(FITC)- rhodaminecouple, tetramethyl rhodamineiso- thiocyan...