Obara Y, Sasaki S, Igarashi Y
Department of Biology, Faculty of Science, Hirosaki University, Aomori, Japan.
Zoolog Sci. 1997 Feb;14(1):57-64. doi: 10.2108/zsj.14.57.
The small Japanese field mouse Apodemus argenteus has the diploid chromosome number of 46, carrying rather large centromeric C-heterochromatin in most of the 44 autosomes and a large amount of C-heterochromatin in the sex chromosomes: the largest subtelocentric X was heterochromatic in almost two-fifth (whole short arm and proximal part of the long arm) of its entire length and the medium-sized acrocentric Y was totally heterochromatic. The C-heterochromatin (C-positive) areas, other than those of the Y and smallest three pairs, had a unique property of "delayed QM-fluorescence", which has not been reported to-date, showing dull QM-fluorescence immediately after exposure to blue light (BL), but gradually turning to bright fluorescence in a few minutes. The fluorescence intensity gradually decreased after attaining its peak, and finally became extinct. A similar pattern of fluorescence was also obtained in DA/DAPI-stained-X chromosome C-heterochromatin, but not in autosomal C-heterochromatin. No such dull-to-bright transition of QM-fluorescence could be obtained by CMA staining, for which the C-positive areas were apparently negative even after overexposure to BL. These facts indicate that the C-positive areas of A. argenteus showing dull-to-bright transition of QM-fluorescence contain A-T rich DNA. The delayed QM-fluorescence was found only in A. argenteus, in thirteen mammalian species so-far examined. Furthermore, this unique property of QM-fluorescence could be artificially altered to non-delayed ordinary type of fluorescence by sequentially pretreating the fixed chromosomes with hydrochloride and barium hydroxide solutions. The cytological implication of the delayed fluorescence in the C-heterochromatin of A. argenteus is briefly discussed.
日本田鼠（Apodemus argenteus）的二倍体染色体数目为46条，在44条常染色体的大多数中携带相当大的着丝粒C-异染色质，在性染色体中携带大量C-异染色质：最大的亚端着丝粒X染色体在其全长的近五分之二（整个短臂和长臂的近端部分）为异染色质，中等大小的近端着丝粒Y染色体完全为异染色质。除Y染色体和最小的三对染色体外，C-异染色质（C阳性）区域具有一种迄今尚未报道的“延迟QM荧光”特性，即在暴露于蓝光（BL）后立即呈现暗淡的QM荧光，但在几分钟内逐渐变为明亮的荧光。荧光强度在达到峰值后逐渐降低，最终消失。在DA/DAPI染色的X染色体C-异染色质中也获得了类似的荧光模式，但在常染色体C-异染色质中未获得。通过CMA染色无法获得这种从暗淡到明亮的QM荧光转变，对于CMA染色，即使过度暴露于蓝光，C阳性区域显然也是阴性。这些事实表明，显示QM荧光从暗淡到明亮转变的日本田鼠C阳性区域含有富含A-T的DNA。在迄今检测的13种哺乳动物中，仅在日本田鼠中发现了延迟QM荧光。此外，通过依次用盐酸和氢氧化钡溶液预处理固定染色体，这种独特的QM荧光特性可以人为改变为非延迟的普通荧光类型。本文简要讨论了日本田鼠C-异染色质中延迟荧光的细胞学意义。
