Molecular evolution of the vesicular transport machinery and the Golgi apparatus

The system of internal membrane-bound compartments involved in protein transport and degradation plays a crucial role in eukaryotic cell biology and yet there has been relatively little investigation of this system's evolution.; Transport between these compartments is accomplished through a complicated set of machinery for crafting, delivering and fusing vesicles. Comparative genomic methods were used to examine the origin and early evolution of this vesicular-transport machinery. Molecular biological and phylogenetic methods were also used to investigate more detailed evolutionary questions of the syntaxins, a component of this machinery. Together, these studies uncovered aspects of the endomembrane system's prokaryotic origins, the early crystalization of the core machinery and the extensive diversification of the syntaxin family though out the course of eukaryotic evolution.; Involved in both secretion and endocytosis, the Golgi apparatus plays a deeply entrenched role in the life of most eukaryotic cells. There are, however, a few eukaryotes that are thought to lack this organelle. The question of primary versus secondary absence of the Golgi apparatus in these lineages impacts our understanding of its evolution in eukaryotes as a whole. Molecular biological and phylogenetic methods were used to establish the sisterhood of one 'Golgi-lacking' lineage (the oxymonads) with Golgi-possessing taxa. Golgi-specific components of the vesicular-transport machinery were also obtained from a variety of 'Golgi-lacking' eukaryotes. In sum, these data suggest that there are no extant eukaryotes that primitively lack the organelle, and that the Golgi apparatus was present in the Last Common Eukaryotic Ancestor.; It appears that the basic machinery for intracellular trafficking, as well as the complete organellar complement of the endomembrane system, was already established before the diversification of the known eukaryotic lineages. This finding underscores the importance of the endomembrane system's place in our cellular makeup and its possible role in eukaryogenesis.