Urata Y, Parmelee S J, Agard D A, Sedat J W
Department of Biochemistry and Biophysics, University of California, San Francisco 94143-0554, USA.
J Cell Biol. 1995 Oct;131(2):279-95. doi: 10.1083/jcb.131.2.279.
We have analyzed the three-dimensional structural details of Drosophila melanogaster polytene chromosome bands and interbands using three-dimensional light microscopy and a novel method of sample preparation that does not involve flattening or stretching the chromosomes. Bands have been visualized in unfixed chromosomes stained with the DNA specific dye 4,6-Diamidino-2-phenylindole (DAPI). Interbands have been visualized using fixed chromosomes that have been immunostained with an antibody to RNA polymerase II. Additionally, these structures have been analyzed using in situ hybridization with probes from specific genetic loci (Notch and white). Bands are seen to be composed of approximately 36 substructural features that measure 0.2-0.4 micron in diameter. We suggest that these substructural features are in fact longitudinal fibers made up of bundles of chromatids. Band shape can be a reproducible characteristic of a particular band and is dependent on the spatial relationship of these bundles, varying from bands with a uniform distribution of bundles to bands with a peripheral concentration of chromatin. Interbands are composed of bundles of chromatids of a similar size and number as those seen in the bands. The distribution of bundles is similar between a band and the neighboring interband, implying that there is a long range organization to the DNA that includes both the coding and the noncoding portions of genes. Finally, we note that the polytene chromosome has a circular shape when viewed in cross section, whether there are one or two homologs present.
我们使用三维光学显微镜和一种不涉及染色体扁平化或拉伸的新型样品制备方法，分析了黑腹果蝇多线染色体带和间带的三维结构细节。通过用DNA特异性染料4,6-二脒基-2-苯基吲哚（DAPI）染色的未固定染色体观察到了带。通过用抗RNA聚合酶II抗体进行免疫染色的固定染色体观察到了间带。此外，使用来自特定基因位点（Notch和white）的探针进行原位杂交分析了这些结构。观察到带由大约36个直径为0.2 - 0.4微米的亚结构特征组成。我们认为这些亚结构特征实际上是由染色单体束组成的纵向纤维。带的形状可以是特定带的可重复特征，并且取决于这些束的空间关系，从束均匀分布的带到染色质外周集中的带各不相同。间带由与带中所见大小和数量相似的染色单体束组成。带和相邻间带之间束的分布相似，这意味着DNA存在包括基因编码和非编码部分的长程组织。最后，我们注意到，无论存在一条还是两条同源染色体，多线染色体在横截面观察时呈圆形。
