Showell Christopher, Cunliffe Vincent T
Centre for Developmental Genetics, School of Medicine and Biomedical Science, University of Sheffield, Firth Court, Western Bank, Sheffield S10 2TN, UK.
Gene. 2002 May 29;291(1-2):95-104. doi: 10.1016/s0378-1119(02)00588-7.
The extra sex combs (esc) gene of Drosophila and its mammalian homologue embryonic ectoderm development (eed) play pivotal roles in establishing Polycomb-group (Pc-G) mediated transcriptional silencing of regulatory genes during early development. We have carried out a two-hybrid screen in yeast to identify maternally expressed proteins that interact directly with the product of the Xenopus eed homologue, Xeed. Xeed-interacting proteins that were recovered in this screen included a maternal Xenopus histone deacetylase (HDACm), the Xeed protein itself, and a Xenopus homologue of Enhancer of zeste (XEZ) - a second member of the Pc-G that is closely related by sequence similarity to histone methyltransferases. We have also identified a novel interaction between Xeed and a component of the Xenopus basal transcription machinery, TAF(II)32. We show for the first time that each of these proteins interacts with the Xeed polypeptide, both in the yeast two-hybrid assay and in vitro using purified recombinant proteins. XEZ, HDACm and TAF(II)32 mRNAs are all strongly co-expressed with Xeed mRNA in the fertilized egg, further suggesting that their encoded proteins could interact with Xeed during early embryonic development. Our observations support a multi-step model for the onset of transcriptional silencing in which Xeed binds to and inhibits the function of the transcription initiation complex and also recruits proteins that mediate the acquisition by associated chromatin of epigenetically heritable, post-translational modifications.
果蝇的额外性梳（esc）基因及其哺乳动物同源物胚胎外胚层发育（eed）在早期发育过程中建立多梳蛋白家族（Pc-G）介导的调控基因转录沉默方面发挥着关键作用。我们在酵母中进行了双杂交筛选，以鉴定与非洲爪蟾eed同源物Xeed的产物直接相互作用的母源表达蛋白。在此筛选中回收的与Xeed相互作用的蛋白包括母源非洲爪蟾组蛋白去乙酰化酶（HDACm）、Xeed蛋白本身以及zeste增强子的非洲爪蟾同源物（XEZ）——Pc-G的第二个成员，其在序列相似性上与组蛋白甲基转移酶密切相关。我们还鉴定出Xeed与非洲爪蟾基础转录机制的一个组分TAF(II)32之间存在新型相互作用。我们首次表明，在酵母双杂交实验以及使用纯化重组蛋白的体外实验中，这些蛋白中的每一种都与Xeed多肽相互作用。XEZ、HDACm和TAF(II)32的mRNA在受精卵中均与Xeed mRNA强烈共表达，进一步表明它们编码的蛋白可能在早期胚胎发育过程中与Xeed相互作用。我们的观察结果支持转录沉默起始的多步骤模型，其中Xeed结合并抑制转录起始复合物的功能，还募集介导相关染色质获得表观遗传可遗传的翻译后修饰的蛋白。
