Hogga Ilham, Karch François
Department of Zoology and Animal Biology, University of Geneva, 30 quai E. Ansermet, Switzerland.
Development. 2002 Nov;129(21):4915-22. doi: 10.1242/dev.129.21.4915.
The Fab-7 chromatin domain boundary insures functional autonomy of the iab-6 and iab-7 cis-regulatory domains in the bithorax complex (BX-C). We have previously shown that chromatin insulators such as gypsy or scs(min) are potent insulators that cannot substitute for Fab-7 function within the BX-C. During the early stages of these swapping experiments, we initially used a fragment of scs that was slightly larger than a minimal scs element (scs(min)). We report that this scs fragment, unlike scs(min), interferes in an orientation-dependent manner with the output of a regulatory region covering 80 kb of DNA (from iab-4 to iab-8). At the core of this orientation-dependent phenotype is a promoter located immediately adjacent to the scs insulator. In one orientation, the promoter traps the activity of the iab-3 through iab-5 cis-regulatory domains, diverting them from the abd-A gene. In the opposite orientation, the promoter is transcribing the iab-7 cis-regulatory domain, resulting in ectopic activation of the latter. Our data suggest that transcription through a Polycomb-Response Element (PRE) interferes with the maintenance of a Polycomb repression complex.
Fab-7染色质结构域边界确保了双胸复合体（BX-C）中iab-6和iab-7顺式调控结构域的功能自主性。我们之前已经表明，诸如gypsy或scs(min)等染色质绝缘子是强大的绝缘子，但它们无法在BX-C中替代Fab-7的功能。在这些交换实验的早期阶段，我们最初使用的scs片段比最小的scs元件（scs(min)）略大。我们报告称，与scs(min)不同，这个scs片段以方向依赖的方式干扰了一个覆盖80 kb DNA（从iab-4到iab-8）的调控区域的输出。这种方向依赖表型的核心是一个紧邻scs绝缘子的启动子。在一种方向上该启动子捕获了从iab-3到iab-5顺式调控结构域的活性，使其从abd-A基因转移。在相反方向上，该启动子转录iab-7顺式调控结构域，导致后者的异位激活。我们的数据表明，通过多梳反应元件（PRE）的转录会干扰多梳抑制复合体的维持。
