Fukushige T, Schroeder D F, Allen F L, Goszczynski B, McGhee J D
Department of Medical Biochemistry, University of Calgary, Alberta, Canada.
Dev Biol. 1996 Sep 15;178(2):276-88. doi: 10.1006/dbio.1996.0218.
The Caenorhabditis elegans digestive tract is composed of four distinct modules derived from separate cell lineages: anterior pharynx from the ABa lineage, posterior pharynx from the MS lineage, gut from the E lineage, and rectum from the ABp lineage. The C. elegans gut esterase gene (ges-1) is normally expressed in the embryonic gut or E lineage. However, expression ges-1 can be switched into cells of the embryonic pharynx and tail by virtue of deleting a tandem pair of WGATAR sites in the ges-1 promoter. Here, we use both laser ablation experiments and genetic analysis to show that cells expressing the WGATAR-deleted ges-1 transgene belong to all three nongut lineages of the digestive tract: ABa, MS, and ABp. We also show that the molecular size and spatial distribution of ges-1 mRNA transcripts produced by either the WGATAR-deleted ges-1 transgene or the undeleted ges-1 control transgene appear correctly regulated, suggesting that the spatial switch in ges-1 expression occurs at the level of transcription initiation. We further show that both the WGATAR-deleted and the undeleted ges-1 transgenes respond appropriately to mutations in a series of maternal effect genes (skn-1, mex-1, pie-1, and pop-1) that alter early blastomere fate. Moreover, the pharynx/tail expression of the WGATAR-deleted ges-1 transgene is abolished by mutations in the zygotic gene pha-4. Finally, we use imprecise transposon excision to produce two independent C. elegans strains with 1- to 2-kb deletions that remove the tandem WGATAR sites from the promoter of the endogenous chromosomal ges-1 gene: in both of these strains, ges-1 is not expressed in the embryonic gut but is expressed in cells of the embryonic pharynx; pharynx expression is weak but incontrovertible. Overall, our results validate previous transgenic analysis of ges-1 control and show further that ges-1 appears to be regulated in a system-specific, rather than a lineage-specific, manner. The multiple facets of ges-1 expression provide an opportunity to investigate how a multicomponent organ system such as the digestive tract is established from diverse cell lineages.
来自ABa谱系的前咽、来自MS谱系的后咽、来自E谱系的肠道以及来自ABp谱系的直肠。秀丽隐杆线虫肠道酯酶基因（ges-1）通常在胚胎肠道或E谱系中表达。然而，通过删除ges-1启动子中的一对串联WGATAR位点，ges-1的表达可以转换到胚胎咽部和尾部的细胞中。在这里，我们使用激光消融实验和遗传分析表明，表达缺失WGATAR的ges-1转基因的细胞属于消化道的所有三个非肠道谱系：ABa、MS和ABp。我们还表明，由缺失WGATAR的ges-1转基因或未缺失的ges-1对照转基因产生的ges-1 mRNA转录本的分子大小和空间分布似乎受到正确调节，这表明ges-1表达的空间转换发生在转录起始水平。我们进一步表明，缺失WGATAR和未缺失的ges-1转基因都能对一系列改变早期卵裂球命运的母体效应基因（skn-1、mex-1、pie-1和pop-1）的突变做出适当反应。此外，缺失WGATAR的ges-1转基因在咽部/尾部的表达被合子基因pha-4的突变所消除。最后，我们使用不精确的转座子切除产生了两个独立的秀丽隐杆线虫菌株，其缺失1至2 kb，从内源染色体ges-1基因的启动子中去除了串联的WGATAR位点：在这两个菌株中，ges-1在胚胎肠道中不表达，但在胚胎咽部的细胞中表达；咽部表达较弱但确凿无疑。总体而言，我们的结果验证了先前对ges-1调控的转基因分析，并进一步表明ges-1似乎是以系统特异性而非谱系特异性的方式受到调控。ges-1表达的多个方面为研究多组分器官系统（如消化道）如何从不同细胞谱系建立提供了机会。
