Elde Nels C, Morgan Garry, Winey Mark, Sperling Linda, Turkewitz Aaron P
Department of Molecular Genetics and Cell Biology, University of Chicago, Chicago, Illinois, United States of America.
PLoS Genet. 2005 Nov;1(5):e52. doi: 10.1371/journal.pgen.0010052. Epub 2005 Nov 4.
Ciliates, although single-celled organisms, contain numerous subcellular structures and pathways usually associated with metazoans. How this cell biological complexity relates to the evolution of molecular elements is unclear, because features in these cells have been defined mainly at the morphological level. Among these ciliate features are structures resembling clathrin-coated, endocytic pits associated with plasma membrane invaginations called parasomal sacs. The combination of genome-wide sequencing in Tetrahymena thermophila with tools for gene expression and replacement has allowed us to examine this pathway in detail. Here we demonstrate that parasomal sacs are sites of clathrin-dependent endocytosis and that AP-2 localizes to these sites. Unexpectedly, endocytosis in Tetrahymena also involves a protein in the dynamin family, Drp1p (Dynamin-related protein 1). While phylogenetic analysis of AP subunits indicates a primitive origin for clathrin-mediated endocytosis, similar analysis of dynamin-related proteins suggests, strikingly, that the recruitment of dynamin-family proteins to the endocytic pathway occurred independently during the course of the ciliate and metazoan radiations. Consistent with this, our functional analysis suggests that the precise roles of dynamins in endocytosis, as well as the mechanisms of targeting, differ in metazoans and ciliates.
纤毛虫虽然是单细胞生物，但含有许多通常与后生动物相关的亚细胞结构和途径。这种细胞生物学复杂性与分子元件进化之间的关系尚不清楚，因为这些细胞中的特征主要是在形态学水平上定义的。这些纤毛虫特征包括类似于网格蛋白包被的、与称为副体囊泡的质膜内陷相关的内吞小窝的结构。嗜热四膜虫的全基因组测序与基因表达和替换工具的结合，使我们能够详细研究这一途径。在这里，我们证明副体囊泡是网格蛋白依赖性内吞作用的位点，并且AP-2定位于这些位点。出乎意料的是，四膜虫中的内吞作用还涉及发动蛋白家族中的一种蛋白质，即Drp1p（发动蛋白相关蛋白1）。虽然对AP亚基的系统发育分析表明网格蛋白介导的内吞作用起源原始，但对发动蛋白相关蛋白的类似分析惊人地表明，发动蛋白家族蛋白被招募到内吞途径是在纤毛虫和后生动物辐射过程中独立发生的。与此一致的是，我们的功能分析表明，发动蛋白在内吞作用中的精确作用以及靶向机制在后生动物和纤毛虫中有所不同。
