Abstract
BackgroundThe Golgi apparatus is a central meeting point for the endocytic and exocytic systems in eukaryotic cells, and the organelle’s dysfunction results in human disease. Its characteristic morphology of multiple differentiated compartments organized into stacked flattened cisternae is one of the most recognizable features of modern eukaryotic cells, and yet how this is maintained is not well understood. The Golgi is also an ancient aspect of eukaryotes, but the extent and nature of its complexity in the ancestor of eukaryotes is unclear. Various proteins have roles in organizing the Golgi, chief among them being the golgins.ResultsWe address Golgi evolution by analyzing genome sequences from organisms which have lost stacked cisternae as a feature of their Golgi and those that have not. Using genomics and immunomicroscopy, we first identify Golgi in the anaerobic amoeba Mastigamoeba balamuthi. We then searched 87 genomes spanning eukaryotic diversity for presence of the most prominent proteins implicated in Golgi structure, focusing on golgins. We show some candidates as animal specific and others as ancestral to eukaryotes.ConclusionsNone of the proteins examined show a phyletic distribution that correlates with the morphology of stacked cisternae, suggesting the possibility of stacking as an emergent property. Strikingly, however, the combination of golgins conserved among diverse eukaryotes allows for the most detailed reconstruction of the organelle to date, showing a sophisticated Golgi with differentiated compartments and trafficking pathways in the common eukaryotic ancestor.
Highlights
The Golgi apparatus is a central meeting point for the endocytic and exocytic systems in eukaryotic cells, and the organelle’s dysfunction results in human disease
M. balamuthi is a free-living anaerobic amoeba, related to Entamoeba, that lacks an identifiable stacked Golgi and that was at one time proposed to be lacking the organelle [23]
We were able to expand this list to a total of 22 proteins (Fig. 1; Additional file 3: Table S2), including the soluble N-ethylmaleimide-sensitive fusion protein attachment protein receptor (SNARE) proteins Syn5, Syn16, and Sec22, the Retromer complex component Vps35, and the components of the multi-subunit tethering complexes that act at the Golgi, COG and TRAPPII
Summary
The Golgi apparatus is a central meeting point for the endocytic and exocytic systems in eukaryotic cells, and the organelle’s dysfunction results in human disease. At the intersection of the secretory and endocytic membrane-trafficking pathways in eukaryotes lies the Golgi. This organelle comprises a series of compartments termed cisternae, providing a platform for protein transport, glycosylation, and targeting. The most salient hallmark of Golgi structure is the presence of multiple membranous compartments, differentiated into cis, medial, and trans-Golgi, and organized into flattened stacks, which facilitates many key Golgi functions in mammalian cells [2]. The golgins are a collection of 11 proteins in mammalian cells defined by the presence of coiled-coil domains, attachment to Golgi membranes near their C-termini (either by tail-anchor transmembrane domains or through binding to small GTPases), and functions that include tethering/ scaffolding [3, 5]. Various additional proteins have been suggested to be involved in Golgi structure and organization (Additional file 1: Table S1)
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