Gindhart J G, King A N, Kaufman T C
Howard Hughes Medical Institute, Indiana University, Bloomington 47405, USA.
Genetics. 1995 Feb;139(2):781-95. doi: 10.1093/genetics/139.2.781.
The Drosophila homeotic gene Sex combs reduced (Scr) controls the segmental identity of the labial and prothoracic segments in the embryo and adult. It encodes a sequence-specific transcription factor that controls, in concert with other gene products, differentiative pathways of tissues in which Scr is expressed. During embryogenesis, Scr accumulation is observed in a discrete spatiotemporal pattern that includes the labial and prothoracic ectoderm, the subesophageal ganglion of the ventral nerve cord and the visceral mesoderm of the anterior and posterior midgut. Previous analyses have demonstrated that breakpoint mutations located in a 75-kb interval, including the Scr transcription unit and 50 kb of upstream DNA, cause Scr misexpression during development, presumably because these mutations remove Scr cis-regulatory sequences from the proximity of the Scr promoter. To gain a better understanding of the regulatory interactions necessary for the control of Scr transcription during embryogenesis, we have begun a molecular analysis of the Scr regulatory interval. DNA fragments from this 75-kb region were subcloned into P-element vectors containing either an Scr-lacZ or hsp70-lacZ fusion gene, and patterns of reporter gene expression were assayed in transgenic embryos. Several fragments appear to contain Scr regulatory sequences, as they direct reporter gene expression in patterns similar to those normally observed for Scr, whereas other DNA fragments direct Scr reporter gene expression in developmentally interesting but non-Scr-like patterns during embryogenesis. Scr expression in some tissues appears to be controlled by multiple regulatory elements that are separated, in some cases, by more than 20 kb of intervening DNA. Interestingly, regulatory sequences that direct reporter gene expression in an Scr-like pattern in the anterior and posterior midgut are imbedded in the regulatory region of the segmentation gene fushi tarazu (ftz), which is normally located between 10 and 20 kb 5' of the Scr transcription start site. This analysis provides an entry point for the study of how Scr transcription is regulated at the molecular level.
果蝇同源异型基因性梳减少（Scr）控制胚胎和成虫中唇节和前胸节的节段特征。它编码一种序列特异性转录因子，该因子与其他基因产物协同控制Scr表达组织的分化途径。在胚胎发生过程中，观察到Scr以离散的时空模式积累，包括唇节和前胸节外胚层、腹神经索的咽下神经节以及前后中肠的内脏中胚层。先前的分析表明，位于一个75kb区间（包括Scr转录单元和50kb上游DNA）的断点突变会导致Scr在发育过程中错误表达，推测是因为这些突变从Scr启动子附近移除了Scr顺式调控序列。为了更好地理解胚胎发生过程中控制Scr转录所需的调控相互作用，我们开始对Scr调控区间进行分子分析。将来自这个75kb区域的DNA片段亚克隆到含有Scr-lacZ或hsp70-lacZ融合基因的P-元件载体中，并在转基因胚胎中检测报告基因的表达模式。几个片段似乎包含Scr调控序列，因为它们指导报告基因以与Scr正常观察到的模式相似的模式表达，而其他DNA片段在胚胎发生过程中指导Scr报告基因以发育上有趣但非Scr样的模式表达。某些组织中的Scr表达似乎受多个调控元件控制，在某些情况下，这些元件被超过20kb的间隔DNA隔开。有趣的是，在前中肠和后中肠中指导报告基因以Scr样模式表达的调控序列嵌入在分割基因腹节基因（ftz）的调控区域中，该区域通常位于Scr转录起始位点5'端10至20kb之间。该分析为研究Scr转录在分子水平上如何调控提供了一个切入点。
