title: The delayed quinacrine mustard fluorescence from the C-blocks of Apodemus argenteus is due to the introduction of nicks into the DNA.
abstract: "Delayed QM-fluorescence" refers to the unusual kinetics of fluorescence from most of the C-heterochromatic regions of the chromosomes of the small Japanese field mouse Apodemus argenteus. When stained with quinacrine mustard (QM-stained), these C-heterochromatic regions emit weak fluorescence immediately after exposure to blue light (BL); they emit bright fluorescence within a few minutes; and the intensity of the fluorescence gradually decreases after maximum fluorescence has been recorded. To elucidate the mechanism of this phenomenon, we used acridine orange staining (AO-staining) and a modified version of the in situ nick-translation method. Focusing on the large C-heterochromatic region (C-block) of the X chromosome, we noted that AO-stained C-blocks emitted greenish fluorescence, while QM-stained and BL-exposed (QM-BL-processed) C-blocks emitted reddish fluorescence upon AO-staining after removal of QM. These findings suggested that the C-block DNA of A. argenteus might undergo a structural change, such as strand breaks, during QM-BL processing. Application of the modified in situ nick-translation method revealed the generation of an appreciable number of nicks in the C-block DNA by QM-BL processing. No such nick formation was observed in the C-blocks of three other mammalian species: Apodemus peninsulae, Microtus montebelli, and Urotrichus talpoides. Our findings support the hypothesis that nick formation due to exposure to BL might play a primary role in inducing delayed QM-fluorescence in the C-blocks of A. argenteus. On the basis of the present and earlier findings, we propose a probable mechanism for delayed QM-fluorescence in A. argenteus chromosomes.
authors.affiliation: Cytogenetics Laboratory, Department of Biofunctional Science, Hirosaki University, Hirosaki, Aomori, Japan.
authors.forename: Michiko
authors.initials: M
authors.lastname: Inuma
authors.forename: Yoshitaka
authors.initials: Y
authors.lastname: Obara
authors.forename: Masaki
authors.initials: M
authors.lastname: Kuro-o
mesh_terms: D000165:Acridine Orange; D000818:Animals; D003411:Arvicolinae / Q000235:genetics; D053904:DNA Breaks, Single-Stranded; D007312:Eulipotyphla / Q000235:genetics; D005260:Female; D005456:Fluorescent Dyes; D006570:Heterochromatin / Q000235:genetics*; D017404:In Situ Hybridization, Fluorescence / Q000379:methods / Q000662:veterinary; D020287:In Situ Nick-End Labeling / Q000379:methods / Q000662:veterinary; D008297:Male; D051189:Murinae / Q000235:genetics*; D011797:Quinacrine Mustard; D014960:X Chromosome / Q000235:genetics
chemical_list: D005456:Fluorescent Dyes; D006570:Heterochromatin; D011797:Quinacrine Mustard; D000165:Acridine Orange