Egan C R, Chung M A, Allen F L, Heschl M F, Van Buskirk C L, McGhee J D
Department of Medical Biochemistry, University of Calgary, Alberta, Canada.
Dev Biol. 1995 Aug;170(2):397-419. doi: 10.1006/dbio.1995.1225.
The Caenorhabditis elegans ges-1 gene (gut esterase No. 1) is expressed only in the intestinal lineage, beginning when the developing gut has only four to eight cells. We analyze the sequence requirements for this tissue-specific gene regulation by injecting deleted/mutated constructs of the ges-1 gene into a viable ges-1 (null) strain of worms and assaying heritably transformed embryos by esterase histochemistry. Many deletion constructs accurately reconstitute the wildtype gut-specific ges-1 expression. However, deletions in the neighborhood of 1100 bp upstream of the ges-1 ATG abolish ges-1 expression in the developing gut, while at the same time activating ges-1 expression in cells of the pharynx/tail that appear to belong to the sister lineage of the gut. Deletions of a 36-bp DNA region containing two tandem WGATAR sequences are sufficient to cause this gut-to-pharynx/tail switch in expression pattern. Deletion of either one of the WGATAR sites or deletion of an adjoining downstream region directs ges-1 expression only in a restricted set of cells of the anterior gut. The ges-1 GATA region acts like a gut-specific enhancer in that: (i) it restores ges-1 gut expression when reinserted elsewhere into the GATA-deleted ges-1 gene; and (ii) multiple copies direct gut expression of an hsp16-lacZ reporter gene. The ges-1 GATA-region also acts as the site of the pharynx/tail repression in that reinsertion elsewhere into the GATA-deleted ges-1 construct causes repression of ges-1 in the pharynx/tail. However, multiple copies of the GATA region are not able to repress the heat-induced expression of an hsp16-lacZ reporter gene, suggesting that the pharynx/tail repression mechanism is specific to the ges-1 environment. Finally, mutation rather than deletion of the individual GATA sequences suggests that gut activation and pharynx/tail repression may be due to separate factors. We present a molecular model that summarizes these results. The ges-1 control circuitry appears surprisingly complex for what might have been expected to be the simplest possible example of a nonessential gene expressed early in a clonal embryonic lineage.
秀丽隐杆线虫的ges-1基因（肠道酯酶1号）仅在肠道谱系中表达，始于发育中的肠道仅有4至8个细胞时。我们通过将ges-1基因的缺失/突变构建体注射到线虫的一个可行的ges-1（无效）菌株中，并通过酯酶组织化学分析可遗传转化的胚胎，来分析这种组织特异性基因调控的序列要求。许多缺失构建体准确地重建了野生型肠道特异性ges-1表达。然而，ges-1 ATG上游1100 bp附近的缺失消除了发育中肠道中的ges-1表达，同时激活了咽部/尾部细胞中的ges-1表达，这些细胞似乎属于肠道的姐妹谱系。包含两个串联WGATAR序列的36 bp DNA区域的缺失足以导致这种表达模式从肠道到咽部/尾部的转变。删除其中一个WGATAR位点或删除相邻的下游区域会导致ges-1仅在前肠的一组受限细胞中表达。ges-1 GATA区域的作用类似于肠道特异性增强子，因为：（i）当它重新插入到GATA缺失的ges-1基因的其他位置时，可恢复ges-1在肠道中的表达；（ii）多个拷贝可指导hsp16-lacZ报告基因在肠道中的表达。ges-1 GATA区域还作为咽部/尾部抑制的位点，因为将其重新插入到GATA缺失的ges-1构建体的其他位置会导致ges-1在咽部/尾部受到抑制。然而，多个拷贝的GATA区域无法抑制hsp16-lacZ报告基因的热诱导表达，这表明咽部/尾部抑制机制对ges-1环境具有特异性。最后，单个GATA序列的突变而非缺失表明肠道激活和咽部/尾部抑制可能是由不同因素导致的。我们提出了一个总结这些结果的分子模型。对于一个可能被认为是在克隆胚胎谱系早期表达的非必需基因的最简单例子来说，ges-1的控制电路似乎出奇地复杂。
