Dubrovsky E B, Dretzen G, Bellard M
Laboratoire de Génétique Moléculaire du CNRS, Unité 184 de Biologie moléculaire, Institut de Chimie Biologique, Faculté de Médecine, Strasbourg, France.
J Mol Biol. 1994 Aug 19;241(3):353-62. doi: 10.1006/jmbi.1994.1512.
At the end of the third larval instar of Drosophila, ecdysone triggers the tissue-specific activation of gene expression. In cytogenetic and molecular studies, the Broad-complex (BR-C) locus has been defined as a key element in the hierarchy of hormonal regulation of gene activity. Here we show that BR-C function is required for the regulation of the small hsp genes, which are clustered in the 67B puff and are known to be activated by heat shock and by ecdysone during development. We have found that the genes of the 67B cluster are expressed differentially in the salivary glands. While hsp23 and hsp27 transcripts accumulate at relatively high levels, those of hsp22 and hsp26 are present at low and intermediate levels, respectively. The complete BR-C deficiency as well as mutations of the npr class reduce the expression of genes hsp23 and hsp27 by 95 to 99%. The analysis of mutants representing two subfunctions of the BR-C-l(1)2Bab and l(1)2Bc, has shown that the latter is principally required for complete hsp induction. As sites of DNase I hypersensitivity in chromatin are believed to correspond to gene regulatory sequences, we have studied the changes of chromatin structure in the 67B region at different states of hsp gene activity. Upon hormonal induction, at the onset of metamorphosis, additional DNase I hypersensitive sites (DHS) appear in the 5' regions, four DHSs are associated with hsp23 and two with hsp27. We suggest that they are due to the binding of the hormone-receptor complex and/or transcription factors, related to ecdysone action. Finally, two DHSs (at -1400 of hsp23 and at -1200 of hsp27) are absent in the mutant nuclei, and thus may correspond to the target sequences for the BR-C-dependent regulatory protein(s).
在果蝇第三龄幼虫末期，蜕皮激素触发基因表达的组织特异性激活。在细胞遗传学和分子研究中，泛素基因复合体（BR-C）位点已被确定为基因活性激素调节层级中的关键元件。在此我们表明，BR-C功能对于小热休克蛋白基因的调节是必需的，这些基因聚集在67B胀泡中，并且已知在发育过程中受热休克和蜕皮激素激活。我们发现，67B簇的基因在唾液腺中差异表达。虽然热休克蛋白23（hsp23）和热休克蛋白27（hsp27）转录本积累水平相对较高，但热休克蛋白22（hsp22）和热休克蛋白26（hsp26）的转录本分别以低水平和中等水平存在。BR-C完全缺失以及npr类突变会使hsp23和hsp27基因的表达降低95%至99%。对代表BR-C的两个亚功能的突变体l(1)2Bab和l(1)2Bc的分析表明，后者是完全诱导热休克蛋白所主要需要的。由于染色质中DNase I超敏位点被认为对应于基因调控序列，我们研究了热休克蛋白基因活性不同状态下67B区域染色质结构的变化。在激素诱导下，在变态开始时，额外的DNase I超敏位点（DHS）出现在5'区域，四个DHS与hsp23相关，两个与hsp27相关。我们认为它们是由于激素-受体复合物和/或与蜕皮激素作用相关的转录因子的结合所致。最后，在突变核中不存在两个DHS（hsp23的-1400处和hsp27的-1200处），因此它们可能对应于BR-C依赖性调节蛋白（们）的靶序列。
