Sipos László, Kozma Gabriella, Molnár Eniko, Bender Welcome
Institute of Genetics, Biological Research Center of Hungarian Academy of Sciences, H-6701 Szeged, Hungary.
Proc Natl Acad Sci U S A. 2007 Jul 24;104(30):12416-21. doi: 10.1073/pnas.0703144104. Epub 2007 Jul 18.
Genes of the Polycomb group maintain long-term, segment-specific repression of the homeotic genes in Drosophila. DNA targets of Polycomb group proteins, called Polycomb response elements (PREs), have been defined by several assays, but they have not been dissected in their original chromosomal context. An enhanced method of gene conversion was developed to generate a series of small, targeted deletions encompassing the best-studied PRE, upstream of the Ultrabithorax (Ubx) transcription unit in the bithorax complex. Deletions that removed an essential 185-bp core of the PRE caused anterior misexpression of Ubx and posterior segmental transformations, including the conversion of the third thoracic segment toward a duplicate first abdominal segment. These phenotypes were variable, suggesting some cooperation between this PRE and others in the bithorax complex. Larger deletions up to 3 kb were also created, which removed DNA sites reportedly needed for Ubx activation, including putative trithorax response elements. These deletions resulted in neither loss of Ubx expression nor loss-of-function phenotypes. Thus, the 3-kb region including the PRE is required for repression, but not for activation, of Ubx.
多梳家族基因维持果蝇同源异型基因的长期、区段特异性抑制。多梳家族蛋白的DNA靶标，即多梳反应元件（PREs），已通过多种检测方法得以确定，但尚未在其原始染色体背景下进行剖析。人们开发了一种增强的基因转换方法，以产生一系列小的、靶向缺失，这些缺失涵盖了位于双胸复合体中超双胸（Ubx）转录单元上游研究得最为透彻的PRE。去除PRE的一个必需的185bp核心的缺失导致Ubx的前部异位表达和后部区段转化，包括第三胸节向重复的第一腹节的转变。这些表型是可变的，表明这个PRE与双胸复合体中的其他PRE之间存在一些协同作用。还创建了长达3kb的更大缺失，这些缺失去除了据报道Ubx激活所需的DNA位点，包括假定的三胸反应元件。这些缺失既未导致Ubx表达丧失，也未导致功能丧失表型。因此，包括PRE的3kb区域是Ubx抑制所必需的，但不是激活所必需的。
