Marshall W F, Dernburg A F, Harmon B, Agard D A, Sedat J W
Department Biochemistry and Biophysics, University of California, San Francisco 94143, USA.
Mol Biol Cell. 1996 May;7(5):825-42. doi: 10.1091/mbc.7.5.825.
Specific interactions of chromatin with the nuclear envelope (NE) in early embryos of Drosophila melanogaster have been mapped and analyzed. Using fluorescence in situ hybridization, the three-dimensional positions of 42 DNA probes, primarily to chromosome 2L, have been mapped in nuclei of intact Drosophila embryos, revealing five euchromatic and two heterochromatic regions associated with the NE. These results predict that there are approximately 15 NE contacts per chromosome arm, which delimit large chromatin loops of approximately 1-2 Mb. These NE association sites do not strictly correlate with scaffold-attachment regions, heterochromatin, or binding sites of known chromatin proteins. Pairs of neighboring probes surrounding one NE association site were used to delimit the NE association site more precisely, suggesting that peripheral localization of a large stretch of chromatin is likely to result from NE association at a single discrete site. These NE interactions are not established until after telophase, by which time the nuclear envelope has reassembled around the chromosomes, and they are thus unlikely to be involved in binding of NE vesicles to chromosomes following mitosis. Analysis of positions of these probes also reveals that the interphase nucleus is strongly polarized in a Rabl configuration which, together with specific targeting to the NE or to the nuclear interior, results in each locus occupying a highly determined position within the nucleus.
果蝇早期胚胎中染色质与核膜（NE）的特异性相互作用已被定位和分析。利用荧光原位杂交技术，已在完整果蝇胚胎的细胞核中定位了42个DNA探针（主要针对2L染色体）的三维位置，揭示了与核膜相关的五个常染色质区域和两个异染色质区域。这些结果预测，每个染色体臂大约有15个核膜接触点，它们界定了大约1-2 Mb的大染色质环。这些核膜结合位点与支架附着区域、异染色质或已知染色质蛋白的结合位点并不严格相关。围绕一个核膜结合位点的相邻探针被用来更精确地界定核膜结合位点，这表明一大段染色质的外周定位可能是由单个离散位点的核膜结合导致的。这些核膜相互作用直到末期之后才建立，此时核膜已在染色体周围重新组装，因此它们不太可能参与有丝分裂后核膜小泡与染色体的结合。对这些探针位置的分析还表明，间期核在拉布尔构型中强烈极化，这与对核膜或核内部的特异性靶向一起，导致每个基因座在细胞核内占据一个高度确定的位置。
