The lipid flippase ATP8A1 regulates the recruitment of ARF effectors to the trans-Golgi Network.

Formation of transport vesicles requires the coordinate activity of the coating machinery that selects cargo into the nascent vesicle and the membrane bending machinery that imparts curvature to the forming bud. Vesicle coating at the trans-Golgi Network (TGN) involves AP1, GGA2 and clathrin, which are recruited to membranes by activated ARF GTPases. The ARF activation at the TGN is mediated by the BIG1 and BIG2 guanine nucleotide exchange factors (GEFs). Membrane deformation at the TGN has been shown to be mediated by lipid flippases, including ATP8A1, that moves phospholipids from the inner to the outer leaflet of the TGN membrane. We probed a possible coupling between the coating and deformation machineries by testing for an interaction between BIG1, BIG2 and ATP8A1, and by assessing whether such an interaction may influence coating efficiency. Herein, we document that BIG1 and BIG2 co-localize with ATP8A1 in both, static and highly mobile TGN elements, and that BIG1 and BIG2 bind ATP8A1. We show that the interaction involves the catalytic Sec7 domain of the GEFs and the cytosolic C-terminal tail of ATP8A1. Moreover, we report that the expression of ATP8A1, but not ATP8A1 lacking the GEF-binding cytosolic tail, increases the generation of activated ARFs at the TGN and increases the selective recruitment of AP1, GGA2 and clathrin to TGN membranes. This occurs without increasing BIG1 or BIG2 levels at the TGN, suggesting that the binding of the ATP8A1 flippase tail to the Sec7 domain of BIG1/BIG2 increases their catalytic activity. Our results support a model in which a flippase component of the deformation machinery impacts the activity of the GEF component of the coating machinery.

Evolution of the ribbon-like organization of the Golgi apparatus in animal cells.

The "ribbon," a structural arrangement in which Golgi stacks connect to each other, is considered to be restricted to vertebrate cells. Although ribbon disruption is linked to various human pathologies, its functional role in cellular processes remains unclear. In this study, we investigate the evolutionary origin of the Golgi ribbon. We observe a ribbon-like architecture in the cells of several metazoan taxa suggesting its early emergence in animal evolution predating the appearance of vertebrates. Supported by AlphaFold2 modeling, we propose that the evolution of Golgi reassembly and stacking protein (GRASP) binding by golgin tethers may have driven the joining of Golgi stacks resulting in the ribbon-like configuration. Additionally, we find that Golgi ribbon assembly is a shared developmental feature of deuterostomes, implying a role in embryogenesis. Overall, our study points to the functional significance of the Golgi ribbon beyond vertebrates and underscores the need for further investigations to unravel its elusive biological roles.

Mutation of S461, in the GOLGA3 phosphorylation site, does not affect mouse spermatogenesis.

Background: Golgin subfamily A member 3 (Golga3), a member of the golgin subfamily A, is highly expressed in mouse testis. The GOLGA3 protein, which contains eight phosphorylation sites, is involved in protein transport, cell apoptosis, Golgi localization, and spermatogenesis. Although it has been previously reported that nonsense mutations in Golga3 cause multiple defects in spermatogenesis, the role of Golga3 in the testis is yet to be clarified. Methods: Immunofluorescence co-localization in cells and protein dephosphorylation experiments were performed. Golga3 S461L/S461Lmice were generated using cytosine base editors. Fertility tests as well as computer-assisted sperm analysis (CASA) were then performed to investigate sperm motility within caudal epididymis. Histological and immunofluorescence staining were used to analyze testis and epididymis phenotypes and TUNEL assays were used to measure germ cell apoptosis in spermatogenic tubules. Results: Immunofluorescence co-localization showed reduced Golgi localization of GOLGA3S465L with some protein scattered in the cytoplasm of HeLa cells .In addition, protein dephosphorylation experiments indicated a reduced band shift of the dephosphorylated GOLGA3S465L, confirming S461 as the phosphorylation site. Golga3 is an evolutionarily conserved gene and Golga3 S461L/S461Lmice were successfully generated using cytosine base editors. These mice had normal fertility and spermatozoa, and did not differ significantly from wild-type mice in terms of spermatogenesis and apoptotic cells in tubules. Conclusions: Golga3 was found to be highly conserved in the testis, and GOLGA3 was shown to be involved in spermatogenesis, especially in apoptosis and Golgi complex-mediated effects. Infertility was also observed in Golga3 KO male mice. Although GOLGA3S465Lshowed reduced localization in the Golgi with some expression in the cytoplasm, this abnormal localization did not adversely affect fertility or spermatogenesis in male C57BL/6 mice. Therefore, mutation of the S461 GOLGA3 phosphorylation site did not affect mouse spermatogenesis.

The factory, the antenna and the scaffold: the three-way interplay between the Golgi, cilium and extracellular matrix underlying tissue function.

The growth and development of healthy tissues is dependent on the construction of a highly specialised extracellular matrix (ECM) to provide support for cell growth and migration and to determine the biomechanical properties of the tissue. These scaffolds are composed of extensively glycosylated proteins which are secreted and assembled into well-ordered structures that can hydrate, mineralise, and store growth factors as required. The proteolytic processing and glycosylation of ECM components is vital to their function. These modifications are under the control of the Golgi apparatus, an intracellular factory hosting spatially organised, protein-modifying enzymes. Regulation also requires a cellular antenna, the cilium, which integrates extracellular growth signals and mechanical cues to inform ECM production. Consequently, mutations in either Golgi or ciliary genes frequently lead to connective tissue disorders. The individual importance of each of these organelles to ECM function is well-studied. However, emerging evidence points towards a more tightly linked system of interdependence between the Golgi, cilium and ECM. This review examines how the interplay between all three compartments underpins healthy tissue. As an example, it will look at several members of the golgin family of Golgi-resident proteins whose loss is detrimental to connective tissue function. This perspective will be important for many future studies looking to dissect the cause and effect of mutations impacting tissue integrity.

An Electron Tomographic Analysis of Giantin-Deficient Golgi Proposes a New Function of the Golgin Protein Family.

The Golgi apparatus is an organelle that mediates modifications, sorting, and transport of proteins and lipids. Golgins are a group of proteins with coiled-coil structures that localize to the Golgi and are thought to function as tethers to facilitate the docking of vesicles, Rab GTPases, and cytoskeleton components to the Golgi stack. Giantin is the longest golgin and has been thought to function as a tether for COPI vesicles along with other golgins, such as p115 and GM130. Contrary to our expectation that the loss of the tether will result in an increase in untethered COPI vesicles in the cytoplasm, our electron microscopy observations showed that the fenestrae normally present in Golgi cisternae were reduced upon Giantin knockdown. We also found that this structural change is accompanied by altered secretion of cargo proteins and cell surface glycosylation. These results indicate that there exists a correlation between Golgi structural changes caused by the loss of Giantin and Golgi function. Here, we describe electron tomography methods for the detection of structural changes in the Golgi.

Pathological (Dis)Similarities in Neuronal Exosome-Derived Synaptic and Organellar Marker Levels Between Alzheimer's Disease and Frontotemporal Dementia.

BACKGROUND: Alzheimer's disease (AD) and frontotemporal dementia (FTD) are pathologically distinct neurodegenerative disorders with certain overlap in cognitive and behavioral symptoms. Both AD and FTD are characterized by synaptic loss and accumulation of misfolded proteins, albeit, in different regions of the brain. OBJECTIVE: To investigate the synaptic and organellar markers in AD and FTD through assessment of the levels of synaptic protein, neurogranin (Ng) and organellar proteins, mitofusin-2 (MFN-2), lysosomal associated membrane protein-2 (LAMP-2), and golgin A4 from neuronal exosomes. METHODS: Exosomes isolated from the plasma of healthy controls (HC), AD and FTD subjects were characterized using transmission electron microscopy. Neurodegenerative status was assessed by measurement of neurofilament light chain (NfL) using Simoa. The pooled exosomal extracts from each group were analyzed for Ng, MFN-2, LAMP-2, and golgin A4 by western blot analysis using enhanced chemiluminescence method of detection. RESULTS: The densitometric analysis of immunoreactive bands demonstrated a 65% reduction of Ng in AD and 53% in FTD. Mitochondrial protein MFN-2 showed a significant reduction by 32% in AD and 46% in FTD. Lysosomal LAMP-2 and Golgi complex associated golgin A4 were considerably increased in both AD and FTD. CONCLUSION: Changes in Ng may reflect the ongoing synaptic degeneration that are linked to cognitive disturbances in AD and FTD. Importantly, the rate of synaptic degeneration was more pronounced in AD. Changes to a similar extent in both the dementia groups in organellar proteins indicates shared mechanisms of protein accumulation/degradation common to both AD and FTD.

Integrative RNA profiling of TBEV-infected neurons and astrocytes reveals potential pathogenic effectors.

Tick-borne encephalitis virus (TBEV), the most medically relevant tick-transmitted flavivirus in Eurasia, targets the host central nervous system and frequently causes severe encephalitis. The severity of TBEV-induced neuropathogenesis is highly cell-type specific and the exact mechanism responsible for such differences has not been fully described yet. Thus, we performed a comprehensive analysis of alterations in host poly-(A)/miRNA/lncRNA expression upon TBEV infection in vitro in human primary neurons (high cytopathic effect) and astrocytes (low cytopathic effect). Infection with severe but not mild TBEV strain resulted in a high neuronal death rate. In comparison, infection with either of TBEV strains in human astrocytes did not. Differential expression and splicing analyses with an in silico prediction of miRNA/mRNA/lncRNA/vd-sRNA networks found significant changes in inflammatory and immune response pathways, nervous system development and regulation of mitosis in TBEV Hypr-infected neurons. Candidate mechanisms responsible for the aforementioned phenomena include specific regulation of host mRNA levels via differentially expressed miRNAs/lncRNAs or vd-sRNAs mimicking endogenous miRNAs and virus-driven modulation of host pre-mRNA splicing. We suggest that these factors are responsible for the observed differences in the virulence manifestation of both TBEV strains in different cell lines. This work brings the first complex overview of alterations in the transcriptome of human astrocytes and neurons during the infection by two TBEV strains of different virulence. The resulting data could serve as a starting point for further studies dealing with the mechanism of TBEV-host interactions and the related processes of TBEV pathogenesis.

PKD-dependent PARP12-catalyzed mono-ADP-ribosylation of Golgin-97 is required for E-cadherin transport from Golgi to plasma membrane.

Adenosine diphosphate (ADP)-ribosylation is a posttranslational modification involved in key regulatory events catalyzed by ADP-ribosyltransferases (ARTs). Substrate identification and localization of the mono-ADP-ribosyltransferase PARP12 at the trans-Golgi network (TGN) hinted at the involvement of ARTs in intracellular traffic. We find that Golgin-97, a TGN protein required for the formation and transport of a specific class of basolateral cargoes (e.g., E-cadherin and vesicular stomatitis virus G protein [VSVG]), is a PARP12 substrate. PARP12 targets an acidic cluster in the Golgin-97 coiled-coil domain essential for function. Its mutation or PARP12 depletion, delays E-cadherin and VSVG export and leads to a defect in carrier fission, hence in transport, with consequent accumulation of cargoes in a trans-Golgi/Rab11-positive intermediate compartment. In contrast, PARP12 does not control the Golgin-245-dependent traffic of cargoes such as tumor necrosis factor alpha (TNFα). Thus, the transport of different basolateral proteins to the plasma membrane is differentially regulated by Golgin-97 mono-ADP-ribosylation by PARP12. This identifies a selective regulatory mechanism acting on the transport of Golgin-97- vs. Golgin-245-dependent cargoes. Of note, PARP12 enzymatic activity, and consequently Golgin-97 mono-ADP-ribosylation, depends on the activation of protein kinase D (PKD) at the TGN during traffic. PARP12 is directly phosphorylated by PKD, and this is essential to stimulate PARP12 catalytic activity. PARP12 is therefore a component of the PKD-driven regulatory cascade that selectively controls a major branch of the basolateral transport pathway. We propose that through this mechanism, PARP12 contributes to the maintenance of E-cadherin-mediated cell polarity and cell-cell junctions.

The Secreted Protein C10orf118 Is a New Regulator of Hyaluronan Synthesis Involved in Tumour-Stroma Cross-Talk.

Interaction between cancer cells and their microenvironment is central in defining the fate of cancer development. Tumour cells secrete signals (cytokines, chemokines, growth factors) that modify the surrounding area, while the niche supplies structures and activities necessary for tumour maintenance and growth. Hyaluronan (HA) is a glycosaminoglycan that constitute cancer cell niche and is known to influence tumour functions such as proliferation, migration and neoangiogenesis. The knowledge of the factors regulating HA synthesis and size is crucial in understanding the mechanisms sustaining tumour development. Here we show that a yet uncharacterized protein secreted by breast tumour cell lines, named c10orf118 (accession number NM_018017 in NCBI/BLAST, and Q7z3E2 according to the Uniprot identifier), with a predicted length of 898 amino acids, can induce the secretion of HA by stromal fibroblasts through the up-regulation of the hyaluronan synthase 2 gene (HAS2). Intracellularly, this protein is localized in the Golgi apparatus with a possible role in vesicle maturation and transport. The expression of c10orf118 was verified in breast cancer patient specimens and was found to be associated with the presence of estrogen receptor that characterizes a good patient survival. We suggest c10orf118 as a new player that influences the HA amount in breast cancer microenvironment and is associated with low aggressiveness of cancer.

The Golgin Protein RUD3 Regulates Fusarium graminearum Growth and Virulence.

Golgins are coiled-coil proteins that play prominent roles in maintaining the structure and function of the Golgi complex. However, the role of golgin proteins in phytopathogenic fungi remains poorly understood. In this study, we functionally characterized the Fusarium graminearum golgin protein RUD3, a homolog of ScRUD3/GMAP-210 in Saccharomyces cerevisiae and mammalian cells. Cellular localization observation revealed that RUD3 is located in the cis-Golgi. Deletion of RUD3 caused defects in vegetative growth, ascospore discharge, deoxynivalenol (DON) production, and virulence. Moreover, the Δrud3 mutant showed reduced expression of tri genes and impairment of the formation of toxisomes, both of which play essential roles in DON biosynthesis. We further used green fluorescent protein (GFP)-tagged SNARE protein SEC22 (SEC22-GFP) as a tool to study the transport between the endoplasmic reticulum (ER) and Golgi and observed that SEC22-GFP was retained in the cis-Golgi in the Δrud3 mutant. RUD3 contains the coiled coil (CC), GRAB-associated 2 (GA2), GRIP-related Arf binding (GRAB), and GRAB-associated 1 (GA1) domains, which except for GA1, are indispensable for normal localization and function of RUD3, whereas only CC is essential for normal RUD3-RUD3 interaction. Together, these results demonstrate how the golgin protein RUD3 mediates retrograde trafficking in the ER-to-Golgi pathway and is necessary for growth, ascospore discharge, DON biosynthesis, and pathogenicity in F. graminearumIMPORTANCEFusarium head blight (FHB) caused by the fungal pathogen Fusarium graminearum is an economically important disease of wheat and other small grain cereal crops worldwide, and limited effective control strategies are available. A better understanding of the regulation mechanisms of F. graminearum development, deoxynivalenol (DON) biosynthesis, and pathogenicity is therefore important for the development of effective control management of this disease. Golgins are attached via their extreme carboxy terminus to the Golgi membrane and are involved in vesicle trafficking and organelle maintenance in eukaryotic cells. In this study, we systematically characterized a highly conserved Golgin protein, RUD3, and found that it is required for vegetative growth, ascospore discharge, DON production, and pathogenicity in F. graminearum Our findings provide a comprehensive characterization of the golgin family protein RUD3 in plant-pathogenic fungus, which could help to identify a new potential target for effective control of this devastating disease.

[Study on plasma Golgi protein 73 and related models in the diagnosis of nonalcoholic fatty liver disease].

Objective: To investigate the relationship between plasma Golgi protein 73 (GP73) levels and the occurrence and development of non-alcoholic fatty liver disease (NAFLD), and to establish a diagnostic model based on this combination with lipid metabolism indicators to clarify its diagnostic efficacy and clinical application value for NAFLD. Methods: 225 cases with NAFLD [diagnosed by ultrasound, transient elastography (FibroScan502) and liver biopsy (some patients)] and 108 healthy controls were selected from the Department of Hepatology and Physical Examination Center of Integrated Traditional Chinese and Western Medicine, The Third Hospital of Hebei Medical University. Clinical data, routine peripheral blood and serum biochemical test results were collected. The plasma GP73 level was detected by enzyme-linked immunosorbent assay. SPSS 21.0 statistical software was used for statistical analysis. Binary logistic regression model was used to calculate the NAFLD diagnostic model. Receiver operating characteristic curve was used to evaluate the NAFLD constructed model diagnostic efficacy. Results: NAFLD incidence was significantly reduced in younger age group, mostly in young and middle-aged male. However, the NAFLD incidence was increased with increasing age in female. The analysis of age ratio composition showed that the average age for NAFLD onset was 20 ~ 50 years old, and the incidence rate was as high as 47% in among 30 ~ 39 years old, but the incidence rate was significantly decreased in over 60 years old (4.00%). GP73 was an independent risk factor for the occurrence and development of NAFLD. The diagnostic models of GBT, GB and GT were established by GP73 (G) combined with body mass index (BMI, B) and serum triglyceride (TG, T), and the results showed that the areas under the curves of GBT, GB and GT models were 0.969, 0.937 and 0.909, respectively. The sensitivity and the specificity were 84.90%, 77.80% and 84.00%, and 95.40%, 95.40% and 82.40%, respectively, P < 0.05. The GBT model had efficacy of best diagnostic performance. Conclusion: NAFLD is more common in young and middle-aged male, but with advanced age, the incidence of female patients gradually increases. Plasma GP73 levels are related to the occurrence and development of NAFLD. The GBT model can be used as a new model for non-invasive diagnosis and one of the indicators for clinical evaluation of diagnostic efficacy of NAFLD.

Living on the edge: the role of Atgolgin-84A at the plant ER-Golgi interface.

The plant Golgi apparatus is responsible for the processing of proteins received from the endoplasmic reticulum (ER) and their distribution to multiple destinations within the cell. Golgi matrix components, such as golgins, have been identified and suggested to function as putative tethering factors to mediate the physical connections between Golgi bodies and the ER network. Golgins are proteins anchored to the Golgi membrane by the C-terminus either through transmembrane domains or interaction with small regulatory GTPases. The golgin N-terminus contains long coiled-coil domains, which consist of a number of α-helices wrapped around each other to form a structure similar to a rope being made from several strands, reaching into the cytoplasm. In animal cells, golgins are also implicated in specific recognition of cargo at the Golgi.Here, we investigate the plant golgin Atgolgin-84A for its subcellular localization and potential role as a tethering factor at the ER-Golgi interface. For this, fluorescent fusions of Atgolgin-84A and an Atgolgin-84A truncation lacking the coiled-coil domains (Atgolgin-84AΔ1-557) were transiently expressed in tobacco leaf epidermal cells and imaged using high-resolution confocal microscopy. We show that Atgolgin-84A localizes to a pre-cis-Golgi compartment that is also labelled by one of the COPII proteins as well as by the tether protein AtCASP. Upon overexpression of Atgolgin-84A or its deletion mutant, transport between the ER and Golgi bodies is impaired and cargo proteins are redirected to the vacuole. LAY DESCRIPTION: The Golgi apparatus is a specialised compartment found in mammalian and plant cells. It is the post office of the cell and packages proteins into small membrane boxes for transport to their destination in the cell. The plant Golgi apparatus consist of many separate Golgi bodies and is responsible for the processing of proteins received from the endoplasmic reticulum (ER) and their distribution to multiple destinations within the cell. Specialised proteins called golgins have been suggested to tether Golgi bodies and the ER. Here we investigate the plant golgin Atgolgin-84A for its exact within the Golgi body and its potential role as a tethering factor at the ER-Golgi interface. For this, we have fused Atgolgin-84A with a fluorescent protein from jellyfish and we are producing this combination in tobacco leaf cells. This allows us to see the protein using laser microscopy. We show that Atgolgin-84A localises to a compartment between the ER and Golgi that is also labelled by the tether protein AtCASP. When Atgolgin-84A is produced in high amounts in the cell, transport between the ER and Golgi bodies is inhibited and proteins are redirected to the vacuole.

ELKS1 Captures Rab6-Marked Vesicular Cargo in Presynaptic Nerve Terminals.

Neurons face unique transport challenges. They need to deliver cargo over long axonal distances and to many presynaptic nerve terminals. Rab GTPases are master regulators of vesicular traffic, but essential presynaptic Rabs have not been identified. Here, we find that Rab6, a Golgi-derived GTPase for constitutive secretion, associates with mobile axonal cargo and localizes to nerve terminals. ELKS1 is a stationary presynaptic protein with Golgin homology that binds to Rab6. Knockout and rescue experiments for ELKS1 and Rab6 establish that ELKS1 captures Rab6 cargo. The ELKS1-Rab6-capturing mechanism can be transferred to mitochondria by mistargeting ELKS1 or Rab6 to them. We conclude that nerve terminals have repurposed mechanisms from constitutive exocytosis for their highly regulated secretion. By employing Golgin-like mechanisms with anchored ELKS extending its coiled-coils to capture Rab6 cargo, they have spatially separated cargo capture from fusion. ELKS complexes connect to active zones and may mediate vesicle progression toward release sites.

Endosome-to-TGN Trafficking: Organelle-Vesicle and Organelle-Organelle Interactions.

Retrograde transport from endosomes to the trans-Golgi network (TGN) diverts proteins and lipids away from lysosomal degradation. It is essential for maintaining cellular homeostasis and signaling. In recent years, significant advancements have been made in understanding this classical pathway, revealing new insights into multiple steps of vesicular trafficking as well as critical roles of ER-endosome contacts for endosomal trafficking. In this review, we summarize up-to-date knowledge about this trafficking pathway, in particular, mechanisms of cargo recognition at endosomes and vesicle tethering at the TGN, and contributions of ER-endosome contacts.

GRASP55: A Multifunctional Protein.

GRASP55 was first found as Golgi cisternae stacking protein. Due to the crucial role of Golgi in vesicular trafficking and protein modification, GRASP55 was found to function in these two aspects. Further investigation revealed that GRASP55 also participates in the unconventional secretory pathway under stress. Moreover, GRASP55 is involved in autophagy initiation and autophagosome maturation, as well as cell activity.

The Golgi apparatus and cell polarity: Roles of the cytoskeleton, the Golgi matrix, and Golgi membranes.

Membrane trafficking plays a crucial role in cell polarity by directing lipids and proteins to specific subcellular locations in the cell and sustaining a polarized state. The Golgi apparatus, the master organizer of membrane trafficking, can be subdivided into three layers that play different mechanical roles: a cytoskeletal layer, the so-called Golgi matrix, and the Golgi membranes. First, the outer regions of the Golgi apparatus interact with cytoskeletal elements, mainly actin and microtubules, which shape, position, and orient the organelle. Closer to the Golgi membranes, a matrix of long coiled-coiled proteins not only selectively captures transport intermediates but also participates in signaling events during polarization of membrane trafficking. Finally, the Golgi membranes themselves serve as active signaling platforms during cell polarity events. We review here the recent findings that link the Golgi apparatus to cell polarity, focusing on the roles of the cytoskeleton, the Golgi matrix, and the Golgi membranes.

Liquid-liquid phase separation of the Golgi matrix protein GM130.

Golgins are an abundant class of peripheral membrane proteins of the Golgi. These very long (50-400 nm) rod-like proteins initially capture cognate transport vesicles, thus enabling subsequent SNARE-mediated membrane fusion. Here, we explore the hypothesis that in addition to serving as vesicle tethers, Golgins may also possess the capacity to phase separate and, thereby, contribute to the internal organization of the Golgi. GM130 is the most abundant Golgin at the cis Golgi. Remarkably, overexpressed GM130 forms liquid droplets in cells analogous to those described for numerous intrinsically disordered proteins with low complexity sequences, even though GM130 is neither low in complexity nor intrinsically disordered. Virtually pure recombinant GM130 also phase-separates into dynamic, liquid-like droplets in close to physiological buffers and at concentrations similar to its estimated local concentration at the cis Golgi.

The Golgi Apparatus of Neocortical Glial Cells During Hibernation in the Syrian Hamster.

Hibernating mammals undergo torpor periods characterized by a general decrease in body temperature, metabolic rate, and brain activity accompanied by complex adaptive brain changes that appear to protect the brain from extreme conditions of hypoxia and low temperatures. These processes are accompanied by morphological and neurochemical changes in the brain including those in cortical neurons such as the fragmentation and reduction of the Golgi apparatus (GA), which both reverse a few hours after arousal from the torpor state. In the present study, we characterized - by immunofluorescence and confocal microscopy - the GA of cortical astrocytes, oligodendrocytes, and microglial cells in the Syrian hamster, which is a facultative hibernator. We also show that after artificial induction of hibernation, in addition to neurons, the GA of glia in the Syrian hamster undergoes important structural changes, as well as modifications in the intensity of immunostaining and distribution patterns of Golgi structural proteins at different stages of the hibernation cycle.

The golgin PpImh1 mediates reversible cisternal stacking in the Golgi of the budding yeast Pichia pastoris.

The adhesive force for cisternal stacking of Golgi needs to be reversible - to be initiated and undone in a continuous cycle to keep up with the cisternal maturation. Microscopic evidence in support of such a reversible nature of stacking, in the form of 'TGN peeling,' has been reported in various species, suggesting a potential evolutionarily conserved mechanism. However, knowledge of such mechanism has remained sketchy. Here, we have explored this issue in the budding yeast Pichia pastoris which harbors stacked Golgi. We observed that deletion of GRIP domain golgin P. pastoris (Pp)IMH1 increases the peeling of late cisterna, causing unstacking of the Golgi stack. Our results suggest that the PpImh1 dimer mediates reversible stacking through a continuous association-dissociation cycle of its GRIP domain to the middle and late Golgi cisterna under the GTP hydrolysis-based regulation of Arl3-Arl1 GTPase cascade switch. The reversible cisternal stacking function of PpImh1 is independent of its vesicle-capturing function. Since GRIP domain proteins are conserved in plants, animals and fungi, it is plausible that this reversible mechanism of Golgi stacking is evolutionarily conserved.This article has an associated First Person interview with the first author of the paper.

The Physiological Functions of the Golgin Vesicle Tethering Proteins.

The golgins comprise a family of vesicle tethering proteins that act in a selective manner to tether transport vesicles at the Golgi apparatus. Tethering is followed by membrane fusion to complete the delivery of vesicle-bound cargo to the Golgi. Different golgins are localized to different regions of the Golgi, and their ability to selectively tether transport vesicles is important for the specificity of vesicle traffic in the secretory pathway. In recent years, our mechanistic understanding of golgin-mediated tethering has greatly improved. We are also beginning to appreciate how the loss of golgin function can impact upon physiological processes through the use of animal models and the study of human disease. These approaches have revealed that loss of a golgin causes tissue-restricted phenotypes, which can vary in severity and the cell types affected. In many cases, it is possible to attribute these phenotypes to a defect in vesicular traffic, although why certain tissues are sensitive to loss of a particular golgin is still, in most cases, unclear. Here, I will summarize recent progress in our understanding of golgins, focusing on the physiological roles of these proteins, as determined from animal models and the study of disease in humans. I will describe what these in vivo analyses have taught us, as well as highlight less understood aspects, and areas for future investigations.