About this Research Topic
At the age of 120 the Golgi apparatus still keeps many of its secrets. Nonetheless, this dynamic organelle – located at the intersection of the secretory and endocytic pathways and characterized by its unique organization into stacks of flattened cisternae – is well known for its important contributions to the transport and modification of endoplasmic reticulum (ER)-derived lipids, proteins and carbohydrates, as well as the sorting of these newly made biosynthetic products to their final intra- or extracellular destinations. During the last decades the protein machineries that carry out these classical Golgi functions have been extensively scrutinized and, as a result, considerable progress has been made in the determination of the molecular mechanisms underlying Golgi structure formation and function. New hypotheses have been put forward, but not without controversy.
First, regarding the molecular machineries that govern Golgi architecture and function, the roles of the “Golgi matrix proteins” have been extensively characterized and novel family members have been identified. In particular, the function of the “golgins” in membrane tethering is now better understood, while the oligomeric GRASP proteins have been implicated in the linking of cisternae into stacks and adjacent stacks into a Golgi ribbon. However, disagreements exist within the field and between different model systems. In contrast to invertebrates, plants and several yeast species, where the stacks function as individual dispersed units, in vertebrate cells multiple Golgi stacks are typically linked together into a ribbon structure close to the microtubule organizing center (MTOC)/centrosome. The significance of this special arrangement, which does not seem to be required for transport as such, remains unknown. Moreover, it remains unclear how the compositional cis-trans polarity of the dynamic Golgi stacks is maintained.
Second, new evidence has been provided to support some of the models on how proteins traverse or stay in the Golgi subcompartments, but a complete mechanistic picture is still under development. Thus, it remains a matter of controversy how different cargo molecules pass through the Golgi stacks – from the cis- or entry side of the organelle to its trans- or exit side. Possible alternative mechanisms include vesicular or tubular trafficking between cisternae, cisternal maturation (progression), or the combination of both. Similarly, several hypothesis have been put forward to explain the mechanisms that govern precise localization and recycling of Golgi resident proteins such as glycosyltransferases, including retrograde vesicular trafficking, recycling through the ER and endosomes, kin recognition and oligomerization. Although some of these models are more dominant in the field, their final approval is still missing.
Third, intriguing new results have uncovered novel functions of the Golgi related to cell physiology. For example, the Golgi has been linked to cell migration, cell division, cell growth and apoptosis, as indicated by the findings showing that these processes are accompanied by the fragmentation of the Golgi ribbon. In addition, how the Golgi responds to cellular stressors is emerging as an interesting new topic. For example, it has been suggested that Golgi proteins play key roles in autophagy and unconventional secretion of cytosolic proteins.
Finally, new information has been provided regarding Golgi function during development. Moreover, structural and functional alterations of the Golgi have been shown to be associated with an increasing number of diseases, including various neurodegenerative disorders, cancer, and viral infection.
Specific sub-topics of this article collection on Golgi dynamics include:
Golgi architecture and function
• Roles of golgins, GRASPs, small GTPases, multisubunit vesicular tethers, SNAREs and coat proteins in functional organization of the Golgi
• Cytoskeleton in Golgi organization and dynamics
• Structure-function relationship of the Golgi
• Golgi organization in different cell types (e.g. neurons, epithelial and muscle cells) and organisms
• Golgi origin and evolution
Golgi trafficking and targeting
• Polarity and the dynamics of Golgi enzymes (glycosyltransferases)
• Transfer, modification, and sorting of cargo through and within the Golgi apparatus
• Golgi cargo receptors
• Golgi entry and exit
• Retrograde trafficking of bacterial toxins
• Membrane contact sites between Golgi and other organelles and their role in lipid transfer
Golgi in cell physiology and stress
• Golgi in mitosis and apoptosis
• Golgi organization during cell differentiation
• Role of Golgi in cell motility
• Golgi in metabolism and catabolism (autophagy)
• Golgi pH and ion balance
• Role of Golgi proteins in unconventional trafficking
• Golgi and intracellular signaling
Golgi defects in development and diseases
• Golgi defects in neurodegeneration (Alzheimer’s, Parkinson’s, ALS)
• Golgi and intracellular pathogens (including bacteria and viruses)
• Golgi and congenital disorders of glycosylation (CDG)
• Golgi protein and lipid glycosylation in development
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