Marti Matthias, Regös Attila, Li Yajie, Schraner Elisabeth M, Wild Peter, Müller Norbert, Knopf Lea G, Hehl Adrian B
Institute of Parasitology, University of Zürich, Switzerland.
J Biol Chem. 2003 Jul 4;278(27):24837-48. doi: 10.1074/jbc.M302082200. Epub 2003 Apr 23.
The protozoan parasite Giardia intestinalis belongs to one of the earliest diverged eukaryotic lineages. This is also reflected in a simple intracellular organization, as Giardia lacks common subcellular compartments such as mitochondria, peroxisomes, and apparently also a Golgi apparatus. During encystation, developmentally regulated formation of large secretory compartments containing cyst wall material occurs. Despite the lack of any morphological similarities, these encystation-specific vesicles (ESVs) show several biochemical characteristics of maturing Golgi cisternae. Previous studies suggested that Golgi structure and function are induced only during encystation in Giardia, giving rise to the hypothesis that ESVs, as a Giardia Golgi equivalent, are generated de novo. Alternatively, ESV compartments could be built on the template structure of a cryptic Golgi in trophozoites in response to ER export of cyst wall material during encystation. We addressed this question by defining the molecular framework of the Giardia secretory apparatus using a comparative genomic approach. Analysis of the corresponding transcriptome during growth and encystation revealed surprisingly little stage-specific regulation. A panel of antibodies was generated against selected marker proteins to investigate the developmental dynamics of the endomembrane system. We show evidence that Giardia accommodates the export of large amounts of cyst wall material through re-organization of membrane compartment(s) in trophozoites with biochemical similarities to ESVs. This suggests that ESVs are selectively stabilized Golgi-like compartments in a unique and archetypical secretory system, which arise from a structural template in trophozoites rather than being generated de novo.
原生动物寄生虫肠道贾第虫属于最早分化的真核生物谱系之一。这也反映在其简单的细胞内组织中，因为贾第虫缺乏常见的亚细胞区室，如线粒体、过氧化物酶体，显然也没有高尔基体。在包囊化过程中，会发生发育调控的、形成含有囊壁物质的大型分泌区室的过程。尽管缺乏任何形态学上的相似性，但这些包囊化特异性囊泡（ESV）显示出成熟高尔基体潴泡的一些生化特征。先前的研究表明，高尔基体的结构和功能仅在贾第虫包囊化期间被诱导，这就产生了一个假说，即ESV作为贾第虫的高尔基体等效物是从头产生的。或者，ESV区室可以在滋养体中隐匿高尔基体的模板结构上构建，以响应包囊化期间囊壁物质的内质网输出。我们通过使用比较基因组学方法定义贾第虫分泌装置的分子框架来解决这个问题。对生长和包囊化过程中相应转录组的分析显示，令人惊讶的是阶段特异性调控很少。针对选定的标记蛋白产生了一组抗体，以研究内膜系统的发育动态。我们有证据表明，贾第虫通过滋养体中膜区室的重组来适应大量囊壁物质的输出，这些膜区室在生化性质上与ESV相似。这表明ESV是独特且典型的分泌系统中选择性稳定的高尔基体样区室，它们源自滋养体中的结构模板，而非从头产生。
