Cell stretching activates an ATM mechano-transduction pathway that remodels cytoskeleton and chromatin

Ataxia telangiectasia mutated (ATM) and ataxia telangiectasia and Rad3-related (ATR) DNA damage response (DDR) kinases contain elastic domains. ATM also responds to reactive oxygen species (ROS) and ATR to nuclear mechanical stress. Mre11 mediates ATM activation following DNA damage; ATM mutations cause ataxia telangiectasia (A-T). Here, using in vivo imaging, electron microscopy, proteomic, and mechano-biology approaches, we study how ATM responds to mechanical stress. We report that cytoskeleton and ROS, but not Mre11, mediate ATM activation following cell deformation. ATM deficiency causes hyper-stiffness, stress fiber accumulation, Yes-associated protein (YAP) nuclear enrichment, plasma and nuclear membrane alterations during interstitial migration, and H3 hyper-methylation. ATM locates to the actin cytoskeleton and, following cytoskeleton stress, promotes phosphorylation of key cytoskeleton and chromatin regulators. Our data contribute to explain some clinical features of patients with A-T and pinpoint the existence of an integrated mechano-response in which ATM and ATR have distinct roles unrelated to their canonical DDR functions.

Human amniotic membrane inhibits migration and invasion of muscle-invasive bladder cancer urothelial cells by downregulating the FAK/PI3K/Akt/mTOR signalling pathway

Bladder cancer is the 10th most commonly diagnosed cancer with the highest lifetime treatment costs. The human amniotic membrane (hAM) is the innermost foetal membrane that possesses a wide range of biological properties, including anti-inflammatory, antimicrobial and anticancer properties. Despite the growing number of studies, the mechanisms associated with the anticancer effects of human amniotic membrane (hAM) are poorly understood. Here, we reported that hAM preparations (homogenate and extract) inhibited the expression of the epithelial-mesenchymal transition markers N-cadherin and MMP-2 in bladder cancer urothelial cells in a dose-dependent manner, while increasing the secretion of TIMP-2. Moreover, hAM homogenate exerted its antimigratory effect by downregulating the expression of FAK and proteins involved in actin cytoskeleton reorganisation, such as cortactin and small RhoGTPases. In muscle-invasive cancer urothelial cells, hAM homogenate downregulated the PI3K/Akt/mTOR signalling pathway, the key cascade involved in promoting bladder cancer. By using normal, non-invasive papilloma and muscle-invasive cancer urothelial models, new perspectives on the anticancer effects of hAM have emerged. The results identify new sites for therapeutic intervention and are prompt encouragement for ongoing anticancer drug development studies.

Molecular, morphological and functional properties of tunnelling nanotubes between normal and cancer urothelial cells: New insights from the in vitro model mimicking the situation after surgical removal of the urothelial tumor

Tunnelling nanotubes (TNTs) are membranous connections that represent a unique type of intercellular communication in different cell types. They are associated with cell physiology and cancer pathology. The possible existence of tunnelling nanotubes communication between urothelial cancer and normal cells has not yet been elucidated. Therefore, we analyzed TNTs formed by T24 cells (human invasive cancer urothelial cells) and normal porcine urothelial (NPU) cells, which serve as surrogate models for healthy human urothelial cells. Monocultures and cocultures of NPU and T24 cells were established and analyzed using live-cell imaging, optical tweezers, fluorescence microscopy, and scanning electron microscopy. TNTs of NPU cells differed significantly from tunnelling nanotubes of T24 cells in number, length, diameter, lipid composition, and elastic properties. Membrane domains enriched in cholesterol/sphingomyelin were present in tunnelling nanotubes of T24 cells but not in NPU cells. The tunnelling nanotubes in T24 cells were also easier to bend than the tunnelling nanotubes in NPU cells. The tunnelling nanotubes of both cell types were predominantly tricytoskeletal, and contained actin filaments, intermediate filaments, and microtubules, as well as the motor proteins myosin Va, dynein, and kinesin 5B. Mitochondria were transported within tunnelling nanotubes in living cells, and were colocalized with microtubules and the microtubule-associated protein dynamin 2. In cocultures, heterocellular tunnelling nanotubes were formed between NPU cells and T24 cells and vice versa. The presence of connexin 43 at the end of urothelial tunnelling nanotubes suggests a junctional connection and the involvement of tunnelling nanotube in signal transduction. In this study, we established a novel urothelial cancer-normal coculture model and showed cells in the minority tend to form tunnelling nanotubes with cells in the majority. The condition with cancer cells in the minority is an attractive model to mimic the situation after surgical resection with remaining cancer cells and may help to understand cancer progression and recurrence. Our results shed light on the biological activity of tunnelling nanotubes and have the potential to advance the search for anticancer drugs that target tunnelling nanotubes.

Contribution of the Golgi apparatus in morphogenesis of a virus-induced cytopathic vacuolar system

Electron tomography reveals four classes of cytopathic vesicles-II (CPV-II) stemming from the host Golgi apparatus after Venezuelan equine encephalitis virus infection.

The Golgi apparatus (GA) in mammalian cells is pericentrosomally anchored and exhibits a stacked architecture. During infections by members of the alphavirus genus, the host cell GA is thought to give rise to distinct mobile pleomorphic vacuoles known as CPV-II (cytopathic vesicle-II) via unknown morphological steps. To dissect this, we adopted a phased electron tomography approach to image multiple overlapping volumes of a cell infected with Venezuelan equine encephalitis virus (VEEV) and complemented it with localization of a peroxidase-tagged Golgi marker. Analysis of the tomograms revealed a pattern of progressive cisternal bending into double-lamellar vesicles as a central process underpinning the biogenesis and the morphological complexity of this vacuolar system. Here, we propose a model for the conversion of the GA to CPV-II that reveals a unique pathway of intracellular virus envelopment. Our results have implications for alphavirus-induced displacement of Golgi cisternae to the plasma membrane to aid viral egress operating late in the infection cycle.

The Golgi complex: An organelle that determines urothelial cell biology in health and disease

The Golgi complex undergoes considerable structural remodeling during differentiation of urothelial cells in vivo and in vitro. It is known that in a healthy bladder the differentiation from the basal to the superficial cell layer leads to the formation of the tightest barrier in our body, i.e., the blood–urine barrier. In this process, urothelial cells start expressing tight junctional proteins, apical membrane lipids, surface glycans, and integral membrane proteins, the uroplakins (UPs). The latter are the most abundant membrane proteins in the apical plasma membrane of differentiated superficial urothelial cells (UCs) and, in addition to well-developed tight junctions, contribute to the permeability barrier by their structural organization and by hindering endocytosis from the apical plasma membrane. By studying the transport of UPs, we were able to demonstrate their differentiation-dependent effect on the Golgi architecture. Although fragmentation of the Golgi complex is known to be associated with mitosis and apoptosis, we found that the process of Golgi fragmentation is required for delivery of certain specific urothelial differentiation cargoes to the plasma membrane as well as for cell–cell communication. In this review, we will discuss the currently known contribution of the Golgi complex to the formation of the blood–urine barrier in normal UCs and how it may be involved in the loss of the blood–urine barrier in cancer. Some open questions related to the Golgi complex in the urothelium will be highlighted.

Comparison of the Cisterna Maturation-Progression Model with the Kiss-and-Run Model of Intra-Golgi Transport: Role of Cisternal Pores and Cargo Domains

The Golgi complex is the central station of the secretory pathway. Knowledge about the mechanisms of intra-Golgi transport is inconsistent. Here, we compared the explanatory power of the cisterna maturation-progression model and the kiss-and-run model. During intra-Golgi transport, conventional cargoes undergo concentration and form cisternal distensions or distinct membrane domains that contain only one membrane cargo. These domains and distension are separated from the rest of the Golgi cisternae by rows of pores. After the arrival of any membrane cargo or a large cargo aggregate at the Golgi complex, the cis-Golgi SNAREs become enriched within the membrane of cargo-containing domains and then replaced by the trans-Golgi SNAREs. During the passage of these domains, the number of cisternal pores decreases. Restoration of the cisternal pores is COPI-dependent. Our observations are more in line with the kiss-and-run model.

Comparative analysis of vertebrates reveals that mouse primordial oocytes do not contain a Balbiani body

Oocytes spend the majority of their lifetime in a primordial state. The cellular and molecular biology of primordial oocytes is largely unexplored; yet, studying these is necessary to understand the mechanisms through which oocytes maintain cellular fitness for decades, and why they eventually fail with age. Here, we develop enabling methods for live-imaging based comparative characterization of Xenopus, mouse and human primordial oocytes. We show that primordial oocytes in all three vertebrate species contain active mitochondria, Golgi apparatus and lysosomes. We further demonstrate that human and Xenopus oocytes have a Balbiani body characterized by a dense accumulation of mitochondria in their cytoplasm. However, despite previous reports, we did not find a Balbiani body in mouse oocytes. Instead, we demonstrate what was previously used as a marker for the Balbiani body in mouse primordial oocytes is in fact a ring-shaped Golgi apparatus that is not functionally associated with oocyte dormancy. Our work provides the first insights into the organisation of the cytoplasm in mammalian primordial oocytes, and clarifies relative advantages and limitations of choosing different model organisms for studying oocyte dormancy.

Diversity of Balbiani body formation in internally and externally fertilizing representatives of Osteoglossiformes (Teleostei: Osteoglossomorpha)

During the early stages of oogenesis, the Balbiani body is formed in the primary oocytes. It consists of the Golgi apparatus, endoplasmic reticulum (ER), and numerous mitochondria aggregated with germ plasm, but its form may differ among animals. Hypothetically, during oogenesis oocytes become adapted to future development in two different environments depending on internal or external fertilization. We aimed to investigate, using light and transmission electron microscopy, the development of the Balbiani body during oogenesis in representatives of Osteoglossiformes, one of the most basal Teleostei groups. We analyzed the structure of oogonia and primary oocytes in the internally fertilizing butterflyfish Pantodon buchholzi and the externally fertilizing Osteoglossum bicirrhosum and Arapaima gigas to compare formation of the Balbiani body in relation to modes of fertilization. We demonstrated that the presence of the germ plasm as well as the fusion and fission of mitochondria are the conserved features of the Bb. However, each species exhibited also some peculiar features, including the presence of three types of ooplasm with different electron density and mitochondria-associated membranes in P. buchholzi; annulate lamellae, complexes of the Golgi apparatus, ER network, and lysosome-like bodies in O. bicirrhosum; as well as karmellae and whorls formed by the lamellae of the ER in A. gigas. Moreover, the form of the germ plasm observed in close contact with mitochondria differed between osteoglossiforms, with a "net-like" structure in P. buchholzi, the presence of numerous strings in O. bicirrhosum, and irregular accumulations in A. gigas. These unique features indicate that the extreme diversity of gamete structure observed so far only in the spermatozoa of osteoglossiforms is also characteristic for oocyte development in these basal teleosts. Possible reason of this variability is a period of about 150 million years of independent evolution of the lineages.

Cytotoxic Activity of LLO Y406A Is Targeted to the Plasma Membrane of Cancer Urothelial Cells

Identification of novel agents for bladder cancer treatment is highly desirable due to the high incidence of tumor recurrence and the risk of progression to muscle-invasive disease. The key feature of the cholesterol-dependent toxin listeriolysin O mutant (LLO Y406A) is its preferential activity at pH 5.7, which could be exploited either directly for selective targeting of cancer cells or the release of accumulated therapeutics from acidic endosomes. Therefore, our goal was to compare the cytotoxic effect of LLO Y406A on cancer cells (RT4) and normal urothelial cells (NPU), and to identify which cell membranes are the primary target of LLO Y406A by viability assays, life-cell imaging, fluorescence, and electron microscopy. LLO Y406A decreased viability, altered cell morphology, provoked membrane blebbing, and induced apoptosis in RT4 cells, while it did not affect NPU cells. LLO Y406A did not cause endosomal escape in RT4 cells, while the plasma membrane of RT4 cells was revealed as the primary target of LLO Y406A. It has been concluded that LLO Y406A has the ability to selectively eliminate cancer urothelial cells through pore-forming activity at the plasma membrane, without cytotoxic effects on normal urothelial cells. This promising selective activity merits further testing as an anti-cancer agent.

Immunohistochemistry as a paramount tool in research of normal urothelium, bladder cancer and bladder pain syndrome

The urothelium, an epithelium of the urinary bladder, primarily functions as blood-urine permeability barrier. The urothelium has a very slow turnover under normal conditions but is capable of extremely fast response to injury. During regeneration urothelium either restores normal function or undergoes altered differentiation pathways, the latter being the cause of several bladder diseases. In this review, we describe the structure of the apical plasma membrane that enables barrier function, the role of urothelium specific proteins uroplakins and the machinery for polarized membrane transports in terminally differentiated superficial umbrella cells. We address key markers, such as keratins, cancer stem cell markers, retinoic acid signalling pathway proteins and transient receptor potential channels and purinergic receptors that drive normal and altered differentiation in bladder cancer and bladder pain syndrome. Finally, we discuss uncertainties regarding research, diagnosis and treatment of bladder pain syndrome. Throughout the review, we emphasise the contribution of immunohistochemistry in advancing our understanding of processes in normal and diseased bladder as well as the most promising possibilities for improved bladder cancer and bladder pain syndrome management.

Standardization of esophageal adenocarcinoma in vitro model and its applicability for model drug testing

FLO-1 cell line represents an important tool in esophageal adenocarcinoma (EAC) research as a verified and authentic cell line to study the disease pathophysiology and antitumor drug screenings. Since in vitro characteristics of cells depend on the microenvironment and culturing conditions, we performed a thorough characterization of the FLO-1 cell line under different culturing conditions with the aim of (1) examining the effect of serum-free growth medium and air–liquid interface (A–L) culturing, which better reflect physiological conditions in vivo and (2) investigating the differentiation potential of FLO-1 cells to mimic the properties of the in vivo esophageal epithelium. Our study shows that the composition of the media influenced the morphological, ultrastructural and molecular characteristics of FLO-1 cells, such as the expression of junctional proteins. Importantly, FLO-1 cells formed spheres at the A–L interface, recapitulating key elements of tumors in the esophageal tube, i.e., direct contact with the gas phase and three-dimensional architecture. On the other hand, FLO-1 models exhibited high permeability to model drugs and zero permeability markers, and low transepithelial resistance, and therefore poorly mimicked normal esophageal epithelium. In conclusion, the identified effect of culture conditions on the characteristics of FLO-1 cells should be considered for standardization, data reproducibility and validity of the in vitro EAC model. Moreover, the sphere-forming ability of FLO-1 cells at the A–L interface should be considered in EAC tumor biology and anticancer drug studies as a reliable and straightforward model with the potential to increase the predictive efficiency of the current in vitro approaches.

Artemisia annua L. Polyphenol-Induced Cell Death Is ROS-Independently Enhanced by Inhibition of JNK in HCT116 Colorectal Cancer Cells

c-Jun N-terminal kinase (JNK) is activated by chemotherapeutic reagents including natural plant polyphenols, and cell fate is determined by activated phospho-JNK as survival or death depending on stimuli and cell types. The purpose of this study was to elucidate the role of JNK on the anticancer effects of the Korean plant Artemisia annua L. (pKAL) polyphenols in p53 wild-type HCT116 human colorectal cancer cells. Cell morphology, protein expression levels, apoptosis/necrosis, reactive oxygen species (ROS), acidic vesicles, and granularity/DNA content were analyzed by phase-contrast microscopy; Western blot; and flow cytometry of annexin V/propidium iodide (PI)-, dichlorofluorescein (DCF)-, acridine orange (AO)-, and side scatter pulse height (SSC-H)/DNA content (PI)-stained cells. The results showed that pKAL induced morphological changes and necrosis or late apoptosis, which were associated with loss of plasma membrane/Golgi integrity, increased acidic vesicles and intracellular granularity, and decreased DNA content through downregulation of protein kinase B (Akt)/β-catenin/cyclophilin A/Golgi matrix protein 130 (GM130) and upregulation of phosphorylation of H2AX at Ser-139 (γ-H2AX)/p53/p21/Bak cleavage/phospho-JNK/p62/microtubule-associated protein 1 light chain 3B (LC3B)-I. Moreover, JNK inhibition by SP600125 enhanced ROS-independently pKAL-induced cell death through downregulation of p62 and upregulation of p53/p21/Bak cleavage despite a reduced state of DNA damage marker γ-H2AX. These findings indicate that phospho-JNK activated by pKAL inhibits p53-dependent cell death signaling and enhances DNA damage signaling, but cell fate is determined by phospho-JNK as survival rather than death in p53 wild-type HCT116 cells.

The Golgi ribbon: mechanisms of maintenance and disassembly during the cell cycle

The Golgi complex (GC) has an essential role in the processing and sorting of proteins and lipids. The GC of mammalian cells is composed of stacks of cisternae connected by membranous tubules to create a continuous network, the Golgi ribbon, whose maintenance requires several core and accessory proteins. Despite this complex structural organization, the Golgi apparatus is highly dynamic, and this property becomes particularly evident during mitosis, when the ribbon undergoes a multistep disassembly process that allows its correct partitioning and inheritance by the daughter cells. Importantly, alterations of the Golgi structure are associated with a variety of physiological and pathological conditions. Here, we review the core mechanisms and signaling pathways involved in both the maintenance and disassembly of the Golgi ribbon, and we also report on the signaling pathways that connect the disassembly of the Golgi ribbon to mitotic entry and progression.

Unlocking Golgi: Why Does Morphology Matter?

The mammalian Golgi apparatus is a highly dynamic organelle, which is normally localized in the juxtanuclear space and plays an essential role in the regulation of cellular homeostasis. While posttranslational modification of cargo is mediated by the resident enzymes (glycosyltransferases, glycosidases, and kinases), the ribbon structure of Golgi and its cisternal stacking mostly rely on the cooperation of coiled-coil matrix golgins. Among them, giantin, GM130, and GRASPs are unique, because they form a tripartite complex and serve as Golgi docking sites for cargo delivered from the endoplasmic reticulum (ER). Golgi undergoes significant disorganization in many pathologies associated with a block of the ER-to-Golgi or intra-Golgi transport, including cancer, different neurological diseases, alcoholic liver damage, ischemic stress, viral infections, etc. In addition, Golgi fragments during apoptosis and mitosis. Here, we summarize and analyze clinically relevant observations indicating that Golgi fragmentation is associated with the selective loss of Golgi residency for some enzymes and, conversely, with the relocation of some cytoplasmic proteins to the Golgi. The central concept is that ER and Golgi stresses impair giantin docking site but have no impact on the GM130-GRASP65 complex, thus inducing mislocalization of giantin-sensitive enzymes only. This cardinally changes the processing of proteins by eliminating the pathways controlled by the missing enzymes and by activating the processes now driven by the GM130-GRASP65-dependent proteins. This type of Golgi disorganization is different from the one induced by the cytoskeleton alteration, which despite Golgi de-centralization, neither impairs function of golgins nor alters trafficking.

Form and function of the Golgi apparatus: scaffolds, cytoskeleton and signalling

In addition to the classical functions of the Golgi in membrane transport and glycosylation, the Golgi apparatus of mammalian cells is now recognised to contribute to the regulation of a range of cellular processes, including mitosis, DNA repair, stress responses, autophagy, apoptosis and inflammation. These processes are often mediated, either directly or indirectly, by membrane scaffold molecules, such as golgins and GRASPs which are located on Golgi membranes. In many cases, these scaffold molecules also link the actin and microtubule cytoskeleton and influence Golgi morphology. An emerging theme is a strong relationship between the morphology of the Golgi and regulation of a variety of signalling pathways. Here, we review the molecular regulation of the morphology of the Golgi, especially the role of the golgins and other scaffolds in the interaction with the microtubule and actin networks. In addition, we discuss the impact of the modulation of the Golgi ribbon in various diseases, such as neurodegeneration and cancer, to the pathology of disease.

Triple labelling of actin filaments, intermediate filaments and microtubules for broad application in cell biology: uncovering the cytoskeletal composition in tunneling nanotubes

We report a protocol for simultaneous triple labelling of intermediate filaments, microtubules and actin filaments. The described procedure offers an optimal preservation of the structure and antigenicity of individual representatives of cytoskeletal elements and is applicable for labelling of tissue samples and cultured cells. Namely, we demonstrate that using this protocol the cytoskeletal elements are well-preserved and detectable in the whole mount urinary bladder tissue pieces, cryosections of the urinary bladder, and in cultured normal and cancer urothelial cells including their delicate intercellular connections such as tunneling nanotubes (TnTs). The protocol uncovers for the first time the co-distribution of actin filaments, intermediate filaments and microtubules in TnTs, which were up to now known as mono- or bi-cytoskeletal structures. Presented triple labelling protocol provides an efficient tool for studying co-distribution of actin filaments, intermediate filaments, and microtubules and therefore offers new insights into their cellular and tissue distribution.

Golgi Dynamics: The Morphology of the Mammalian Golgi Apparatus in Health and Disease

In vertebrate cells the Golgi consists of individual stacks fused together into a compact ribbon structure. The function of the ribbon structure of the Golgi has only begun to be appreciated (De Matteis et al., 2008; Gosavi and Gleeson, 2017; Wei and Seemann, 2017). Recent advances have identified a role for the Golgi in the regulation of a broad range of cellular processes and of particular interest is that the modulation of the Golgi ribbon is associated with regulation of a number of signaling pathways (Makhoul et al., 2018). Various cell responses, such as inflammation, and various disorders and diseases, including neurodegeneration and cancer, are associated with the loss of the Golgi ribbon and the appearance of a dispersed or semi-dispersed Golgi. Often the dispersed Golgi is referred to as a “fragmented” morphology. However, the description of a dispersed Golgi ribbon as “fragmented” is inadequate as it does not accurately define the morphological state of the Golgi. This issue is particularly relevant as there are an increasing number of reports describing Golgi fragmentation under physiological and pathological conditions. Knowledge of the precise Golgi architecture is relevant to an appreciation of the functional status of the Golgi apparatus and the underlying molecular mechanism for the contribution of the Golgi to different cellular processes. Here we propose a classification to define the various morphological states of the non-ribbon architecture of the Golgi in mammalian cells as a guide to more precisely define the relationship between the morphological and functional status of this organelle.

Positioning of the Centrosome and Golgi Complex

For over a century, the centrosome has been an organelle more easily tracked than understood, and the study of its peregrinations within the cell remains a chief underpinning of its functional investigation. Increasing attention and new approaches have been brought to bear on mechanisms that control centrosome localization in the context of cleavage plane determination, ciliogenesis, directional migration, and immunological synapse formation, among other cellular and developmental processes. The Golgi complex, often linked with the centrosome, presents a contrasting case of a pleiomorphic organelle for which functional studies advanced somewhat more rapidly than positional tracking. However, Golgi orientation and distribution has emerged as an area of considerable interest with respect to polarized cellular function. This chapter will review our current understanding of the mechanism and significance of the positioning of these organelles.

Role of Intracellular Transport in the Centriole-Dependent Formation of Golgi Ribbon

The intracellular transport is the most confusing issue in the field of cell biology. The Golgi complex (GC) is the central station along the secretory pathway. It contains Golgi glycosylation enzymes, which are responsible for protein and lipid glycosylation, and in many cells, it is organized into a ribbon. Position and structure of the GC depend on the position and function of the centriole. Here, we analyze published data related to the role of centriole and intracellular transport (ICT) for the formation of Golgi ribbon and specifically stress the importance of the delivery of membranes containing cargo and membrane proteins to the cell centre where centriole/centrosome is localized. Additionally, we re-examined the formation of Golgi ribbon from the point of view of different models of ICT.

Helical organization of microtubules occurs in a minority of tunneling membrane nanotubes in normal and cancer urothelial cells

Tunneling membrane nanotubes (TnTs) are membrane protrusions connecting nearby or distant cells in vitro and in vivo. Functions of TnTs in cellular processes are various and rely on TnT structure, which also depends on cytoskeletal composition. In the present study, we focused on the organization of microtubules (MTs) and intermediate filaments (IFs) in TnTs of urothelial cells. We analysed TnTs of normal porcine urothelial cells, which morphologically and physiologically closely resemble normal human urothelial cells, and of cancer cells derived from invasive human urothelial neoplasm. Wide-field fluorescence, confocal and super-resolution microscopy techniques, together with image analyses and 3D reconstructions enlightened specific MT-IF organization in TnTs, and for the first time revealed that MTs and IFs co-occur in the majority of normal and cancer urothelial cell TnTs. Our findings show that in the initiation segment of TnTs, MTs are cross-linked with each other into filamentous network, however in the middle and the attaching segment of TnT, MTs can helically enwrap IFs, the phenomenon that has not been shown before within the TnTs. In this study, we assess MT-IF co-occurrence in TnTs and present evidence that such helical organization of MTs enwrapping IFs is only occurring in a minority of the TnTs. We also discuss the possible cell-biological and physiological reasons for helical organization of MTs in TnTs.

The Golgi architecture and cell sensing

An array of signalling molecules are located at the Golgi apparatus, including phosphoinositides, small GTPases, kinases, and phosphatases, which are linked to multiple signalling pathways. Initially considered to be associated predominantly with membrane trafficking, signalling pathways at the Golgi are now recognised to regulate a diverse range of higher-order functions. Many of these signalling pathways are influenced by the architecture of the Golgi. In vertebrate cells, the Golgi consists of individual stacks fused together into a compact ribbon structure and the function of this ribbon structure has been enigmatic. Notably, recent advances have identified a role for the Golgi ribbon in regulation of cellular processes. Fragmentation of the Golgi ribbon results in modulation of many signalling pathways. Various diseases and disorders, including cancer and neurodegeneration, are associated with the loss of the Golgi ribbon and the appearance of a dispersed fragmented Golgi. Here, we review the emerging theme of the Golgi as a cell sensor and highlight the relationship between the morphological status of the Golgi in vertebrate cells and the modulation of signalling networks.

Reuse of bladder mucosa explants provides a long lasting source of urothelial cells for the establishment of differentiated urothelia

Organ explant cultures are well-established in vitro models that are used to study normal cell biological and regeneration processes as well as carcinogenesis. Primary urothelial cultures from bladder mucosa explants are highly differentiated and are thus broadly used as in vitro experimental equivalents of native urothelial tissue. Since experiments on differentiated urothelial cultures from bladder mucosa explants currently allow only a single use of explants, establishment of sufficient quantities of cultures requires large numbers of sacrificed animals. There is thus a great need for a cheaper approach with less ethical dilemmas. Herein, we demonstrate that mouse bladder mucosa explants can be reused. Reused explants produce outgrowths with highly differentiated urothelia, just like primary explants. Even after being recycled ten times, urothelial outgrowths have the supramolecular and ultrastructural features that are comparable to the native urothelium. Ten times reused explants produce superficial urothelial cells that express uroplakins in the apical plasma membrane, claudin-8 in the tight junctions, and have a subapical network of cytokeratin 20. Basal urothelial cells in urothelial outgrowths of ten times reused explants express p63 which indicates that these urothelial outgrowths have a persistent proliferative capacity. Using our approach, one can perform experiments that were previously not feasible due to low quantities of donor tissue. The method also offers opportunity for effective use of scarce healthy human urothelial tissue.

trans-Golgi network-bound cargo traffic

Cargo following the retrograde trafficking are sorted at endosomes to be targeted the trans-Golgi network (TGN), a central receiving organelle. Though molecular requirements and their interaction networks have been somewhat established, the complete understanding of the intricate nature of their action mechanisms in every step of the retrograde traffic pathway remains unachieved. This review focuses on elucidating known functions of key regulators, including scission factors at the endosome and tethering/fusion mediators at the receiving dock, TGN, as well as a diverse range of cargo.

Co-culturing porcine normal urothelial cells, urinary bladder fibroblasts and smooth muscle cells for tissue engineering research

New strategies for culturing and co-culturing of the main types of urinary bladder cells are essential for successful establishment of biomimetic in vitro models, which could be applied for research into, and management of, diverse urological disorders. Porcine normal urothelial cells are available in nearly unlimited amounts and have many properties equivalent to human urothelial cells. In the present study, we established normal differentiated porcine urothelial cells in co-cultures with porcine urinary bladder normal fibroblasts and/or smooth muscle cells. The optimal culture medium for establishment of differentiated urothelial cells, demonstrated by positive immunofluorescence of uroplakins, cytokeratins (CK 7, CK 20), zonula occludens 1 (ZO-1), claudin 4, claudin 8, and E-cadherin, was the medium composed of equal parts of Advanced Dulbecco's modified Eagle's medium (A-DMEM) and MCDB 153 medium with physiological calcium concentration of 2.5 mM and without fetal bovine serum, named UroM (+Ca²⁺  - S). This medium was also proven to be suitable for culturing of bladder fibroblasts and smooth muscle cells and co-culturing of urothelial cells with these mesenchymal cells. Urothelial cell differentiation was optimal in UroM (+Ca²⁺  - S) medium in all co-culture conditions and when compared to all conditioned-media combinations. To summarize, these strategies for culturing and co-culturing of urinary bladder urothelial cells with mesenchymal cells could be used as new in vitro models for future basic and applicable research of the urinary bladder and thus potentially also for translational tissue engineering studies.

Uroplakin traffic through the Golgi apparatus induces its fragmentation: new insights from novel in vitro models

Uroplakins (UPs) play an essential role in maintaining an effective urothelial permeability barrier at the level of superficial urothelial cell (UC) layer. Although the organization of UPs in the apical plasma membrane (PM) of UCs is well known, their transport in UCs is only partially understood. Here, we dissected trafficking of UPs and its differentiation-dependent impact on Golgi apparatus (GA) architecture. We demonstrated that individual subunits UPIb and UPIIIa are capable of trafficking from the endoplasmic reticulum to the GA in UCs. Moreover, UPIb, UPIIIa or UPIb/UPIIIa expressing UCs revealed fragmentation and peripheral redistribution of Golgi-units. Notably, expression of UPIb or UPIb/UPIIIa triggered similar GA fragmentation in MDCK and HeLa cells that do not express UPs endogenously. The colocalization analysis of UPIb/UPIIIa-EGFP and COPI, COPII or clathrin suggested that UPs follow constitutively the post-Golgi route to the apical PM. Depolymerisation of microtubules leads to complete blockade of the UPIb/UPIIIa-EGFP post-Golgi transport, while disassembly of actin filaments shows significantly reduced delivery of UPIb/UPIIIa-EGFP to the PM. Our findings show the significant effect of the UPs expression on the GA fragmentation, which enables secretory Golgi-outpost to be distributed as close as possible to the sites of cargo delivery at the PM.

Chitosan hydrochloride has no detrimental effect on bladder urothelial cancer cells

Bladder cancer is among the most common and aggressive human malignant carcinomas, thus targeting and removal of bladder cancer cells is still a challenge. Although it is well known that chitosan hydrochloride (CH-HCl) causes desquamation of normal urothelial cells, its effect on cancer urothelial cells has not been recognized yet. In this in vitro study, we analyzed the cytotoxicity of 0.05% CH-HCl on three urothelial models: two cancer urothelial models, i.e. invasive and papillary urothelial neoplasms, and a normal urothelial model. The cytotoxicity of CH-HCl was evaluated with viability tests, transepithelial resistance (TER) measurements, and electron microscopy. TER measurements showed that 15-minute treatment with CH-HCl caused no reduction in TER of the cancer models, whereas the TER of the normal urothelial model significantly decreased. Furthermore, after CH-HCl treatment, the viability of cancer cells was reduced by only 5%, whereas the viability of normal cells was reduced by 30%. Ultrastructural analysis revealed necrotic cell death in all cases. We have demonstrated that although CH-HCl increases the mortality of cancer urothelial cells, it increases the mortality of normal urothelial cells even more so. However, shorter 2-minute CH-HCl treatment only temporarily increases the permeability of normal urothelial model, i.e. disrupts tight junctions and reduces TER without comprising cell viability, and enables the complete recovery of the permeability barrier after 24h. Overall, our results suggest that CH-HCl cannot be used as a self-sufficient anticancer agent for urothelial bladder cancer treatment; nevertheless a possibility of its use as an enhancer of cytostatic treatment is discussed.

Depletion of the human N-terminal acetyltransferase hNaa30 disrupts Golgi integrity and ARFRP1 localization

The organization of the Golgi apparatus (GA) is tightly regulated. Golgi stack scattering is observed in cellular processes such as apoptosis and mitosis, and has also been associated with disruption of cellular lipid metabolism and neurodegenerative diseases. Our studies show that depletion of the human N-α-acetyltransferase 30 (hNaa30) induces fragmentation of the Golgi stack in HeLa and CAL-62 cell lines. The GA associated GTPase ADP ribosylation factor related protein 1 (ARFRP1) was previously shown to require N-terminal acetylation for membrane association and based on its N-terminal sequence, it is likely to be a substrate of hNaa30. ARFRP1 is involved in endosome-to-trans-Golgi network (TGN) traffic. We observed that ARFRP1 shifted from a predominantly cis-Golgi and TGN localization to localizing both Golgi and non-Golgi vesicular structures in hNaa30-depleted cells. However, we did not observe loss of membrane association of ARFRP1. We conclude that hNaa30 depletion induces Golgi scattering and induces aberrant ARFRP1 Golgi localization.

Biocompatibility of different nanostructured TiO2 scaffolds and their potential for urologic applications

Despite great efforts in tissue engineering of the ureter, urinary bladder, and urethra, further research is needed in order to improve the patient's quality of life and minimize the economic burden of different lower urinary tract disorders. The nanostructured titanium dioxide (TiO₂) scaffolds have a wide range of clinical applications and are already widely used in orthopedic or dental medicine. The current study was conducted to synthesize TiO₂ nanotubes by the anodization method and TiO₂ nanowires and nanospheres by the chemical vapor deposition method. These scaffolds were characterized with scanning electron microscopy (SEM) and X-ray diffraction (XRD) methods. In order to test the urologic applicability of generated TiO₂ scaffolds, we seeded the normal porcine urothelial (NPU) cells on TiO₂ nanotubes, TiO₂ nanowires, TiO₂ nanospheres, and on the standard porous membrane. The viability and growth of the cells were monitored everyday, and after 3 weeks of culturing, the analysis with scanning electron microscope (SEM) was performed. Our results showed that the NPU cells were attached on all scaffolds; they were viable and formed a multilayered epithelium, i.e., urothelium. The apical plasma membrane of the majority of superficial NPU cells, grown on all three different TiO₂ scaffolds and on the porous membrane, exhibited microvilli; thus, indicating that they were at a similar differentiation stage. The maximal caliper diameter measurements of superficial NPU cells revealed significant alterations, with the largest cells being observed on nanowires and the smallest ones on the porous membrane. Our findings indicate that different nanostructured TiO₂ scaffolds, especially nanowires, have a great potential for tissue engineering and should be further investigated for various urologic applications.

Intracellular Golgi Complex organization reveals tissue specific polarity during zebrafish embryogenesis

BACKGROUND

Cell polarity is essential for directed migration of mesenchymal cells and morphogenesis of epithelial tissues. Studies in cultured cells indicate that a condensed Golgi Complex (GC) is essential for directed protein trafficking to establish cell polarity underlying directed cell migration. Dynamic changes of the GC intracellular organization during early vertebrate development remain to be investigated.

RESULTS

We used antibody labeling and fusion proteins in vivo to study the organization and intracellular placement of the GC during early zebrafish embryogenesis. We found that the GC was dispersed into several puncta containing cis- and trans-Golgi Complex proteins, presumably ministacks, until the end of the gastrula period. By early segmentation stages, the GC condensed in cells of the notochord, adaxial mesoderm, and neural plate, and its intracellular position became markedly polarized away from borders between these tissues.

CONCLUSIONS

We find that GC is dispersed in early zebrafish cells, even when cells are engaged in massive gastrulation movements. The GC accumulates into patches in a stage and cell-type specific manner, and becomes polarized away from borders between the embryonic tissues. With respect to tissue borders, intracellular GC polarity in notochord is independent of mature apical/basal polarity, Wnt/PCP, or signals from adaxial mesoderm. Developmental Dynamics 245:678-691, 2016. © 2016 Wiley Periodicals, Inc.

Highly Selective Anti-Cancer Activity of Cholesterol-Interacting Agents Methyl-β-Cyclodextrin and Ostreolysin A/Pleurotolysin B Protein Complex on Urothelial Cancer Cells

Cholesterol content can vary distinctly between normal and cancer cells, with elevated levels in cancer cells. Here, we investigated cholesterol sequestration with methyl-β-cyclodextrin (MCD), and pore-formation with the ostreolysin A/pleurotolysin B (OlyA/PlyB) protein complex that binds to cholesterol/sphingomyelin-rich membrane domains. We evaluated the effects on viability of T24 invasive and RT4 noninvasive human urothelial cancer cells and normal porcine urothelial (NPU) cells. Cholesterol content strongly correlated with cancerous transformation, as highest in the T24 high-grade invasive urothelial cancer cells, and lowest in NPU cells. MCD treatment induced prominent cell death of T24 cells, whereas OlyA/PlyB treatment resulted in greatly decreased viability of the RT4 low-grade noninvasive carcinoma cells. Biochemical and transmission electron microscopy analyses revealed that MCD and OlyA/PlyB induce necrotic cell death in these cancer cells, while viability of NPU cells was not significantly affected by either treatment. We conclude that MCD is more toxic for T24 high-grade invasive urothelial cancer cells, and OlyA/PlyB for RT4 low-grade noninvasive urothelial cancer cells, and neither is toxic for NPU cells. The cholesterol and cholesterol/sphingomyelin-rich membrane domains in urothelial cancer cells thus constitute a selective therapeutic target for elimination of urothelial cancer cells.

Trans-membrane area asymmetry controls the shape of cellular organelles

Membrane organelles often have complicated shapes and differ in their volume, surface area and membrane curvature. The ratio between the surface area of the cytosolic and luminal leaflets (trans-membrane area asymmetry (TAA)) determines the membrane curvature within different sites of the organelle. Thus, the shape of the organelle could be critically dependent on TAA. Here, using mathematical modeling and stereological measurements of TAA during fast transformation of organelle shapes, we present evidence that suggests that when organelle volume and surface area are constant, TAA can regulate transformation of the shape of the Golgi apparatus, endosomal multivesicular bodies, and microvilli of brush borders of kidney epithelial cells. Extraction of membrane curvature by small spheres, such as COPI-dependent vesicles within the Golgi (extraction of positive curvature), or by intraluminal vesicles within endosomes (extraction of negative curvature) controls the shape of these organelles. For instance, Golgi tubulation is critically dependent on the fusion of COPI vesicles with Golgi cisternae, and vice versa, for the extraction of membrane curvature into 50–60 nm vesicles, to induce transformation of Golgi tubules into cisternae. Also, formation of intraluminal ultra-small vesicles after fusion of endosomes allows equilibration of their TAA, volume and surface area. Finally, when microvilli of the brush border are broken into vesicles and microvilli fragments, TAA of these membranes remains the same as TAA of the microvilli. Thus, TAA has a significant role in transformation of organelle shape when other factors remain constant.

The complete functional recovery of chitosan-treated biomimetic hyperplastic and normoplastic urothelial models

The urinary tract is exposed to a variety of possible injures that may lead to organ damage or loss, and thus, the establishment of valid in vitro urothelial models to study the mechanism of drug candidates is necessary. This study is the first to investigate the effect of chitosan on urothelia in vitro and to evaluate whether chitosan-treated urothelial models can regenerate in vitro and reestablish a functional urothelium. Biomimetic hyperplastic and normoplastic urothelial models were used to test the effect of chitosan (0.05%) on partially and highly differentiated urothelial cells (UCs) by monitoring their molecular, ultrastructural, and physiological changes for 3 weeks. Chitosan caused an immediate and complete loss of transepithelial resistance (TER), tight junction disruption, cytopathological changes of UCs, and consequently enhanced the permeability of partially and highly differentiated urothelial models. However, 3 weeks after chitosan treatment, TER was reestablished, tight junctions resealed, permeability decreased, and progressive differentiation stages of newly exposed superficial UCs expressing uroplakins and tight junction protein claudin-8 were found. The in vitro models regenerated and reestablished urothelia with a tight barrier. The biomimetic urothelial models represent appropriate in vitro models for studying urothelial drug candidates as well as evaluating drug permeabilities and their intracellular function. Understanding the possible intracellular function of chitosan could significantly advance approaches to treating urothelial-specific diseases.

A novel strain of porcine adenovirus detected in urinary bladder urothelial cell culture

Contamination of cell cultures is the most common problem encountered in cell culture laboratories. Besides the secondary cell contaminations often occurring in the cell laboratories, the contaminations originating from donor animal or human tissue are equally as common, but usually harder to recognize and as such require special attention. The present study describes the detection of porcine adenovirus (PAdV), strain PAdV-SVN1 in cultures of normal porcine urothelial (NPU) cells isolated from urinary bladders of domestic pigs. NPU cell cultures were evaluated by light microscopy (LM), polymerase chain reaction (PCR), and additionally assessed by transmission electron microscopy (TEM). Characteristic ultrastructure of virions revealed the infection with adenovirus. The adenoviral contamination was further identified by the sequence analysis, which showed the highest similarity to recently described PAdV strain PAdV-WI. Additionally, the cell ultrastructural analysis confirmed the life-cycle characteristic for adenoviruses. To closely mimic the in vivo situation, the majority of research on in vitro models uses cell cultures isolated from human or animal tissue and their subsequent passages. Since the donor tissue could be a potential source of contamination, the microbiological screening of the excised tissue and harvested cell cultures is highly recommended.

Membrane lipids and proteins as modulators of urothelial endocytic vesicles pathways

The increased studies on urinary bladder umbrella cells as an important factor for maintaining the permeability barrier have suggested new pathways for the discoidal/fusiform endocytic vesicles which is one of the main features of the umbrella cells. The biological role of these vesicles was defined, for many years, as a membrane reservoir for the umbrella cell apical plasma membrane which are subject to an increased tension during the filling phase of the micturition cycle and, therefore, the vesicles are fused with the apical membrane. Upon voiding, the added membrane is reinserted via a non-clathrin or caveolin-dependant endocytosis thereby restoring the vesicle cytoplasmic pool. However, in the last decade, new evidence appeared indicating alternative pathways of the endocytic vesicles different than the cycling process of exocytosis/endocytosis. The purpose of this review is to analyze the molecular modulators, such as membrane lipids and proteins, in the permeability of endocytic vesicles, the sorting of endocytosed material to lysosomal degradation pathway and recycling of both membrane and fluid phases.

Correlative study of functional and structural regeneration of urothelium after chitosan-induced injury

High transepithelial electrical resistance (TEER) demonstrates a functional permeability barrier of the normal urothelium, which is maintained by a layer of highly differentiated superficial cells. When the barrier is challenged, a quick regeneration is induced. We used side-by-side diffusion chambers as an ex vivo system to determine the time course of functional and structural urothelial regeneration after chitosan-induced injury. The exposure of the urothelium to chitosan caused a 60 % decrease in TEER, the exposure of undifferentiated urothelial cells to the luminal surface and leaky tight junctions. During the regeneration period (350 min), TEER recovered to control values after approximately 200 min, while structural regeneration continued until 350 min after injury. The tight junctions are the earliest and predominant component of the barrier to appear, while complete barrier regeneration is achieved by delayed superficial cell terminal differentiation. The barrier function and the structure of untreated urothelium were unaffected in side-by-side diffusion chambers for at least 6 h. The urinary bladder tissue excised from an animal thus retains the ability to maintain and restore the transepithelial barrier and cellular ultrastructure for a sufficient period to allow for studies of regeneration in ex vivo conditions.

Air-liquid and liquid-liquid interfaces influence the formation of the urothelial permeability barrier in vitro

Optimizing culture conditions is known to be crucial for the differentiation of urothelial cell cultures and the formation of the permeability barrier. However, so far, no data exist to confirm if air-liquid (AL) and liquid-liquid (LL) interfaces are physiologically relevant during urothelial differentiation and barrier formation. To reveal the influence of interfaces on the proliferation, differentiation, and barrier formation of the urothelial cells (UCs) in vitro, we cultured UCs under four different conditions, i.e., at the AL or LL interfaces with physiological calcium concentration and without serum or without physiological calcium concentration and with serum. For each of the four models, the urothelial integrity was tested by measuring the transepithelial resistance (TER), and the differentiation stage was examined by immunolabeling of differentiation-related markers and ultrastructural analysis. We found that the UCs at a LL interface, regardless of the presence or absence of calcium or serum, form the urothelium with more cell layers and achieve a higher TER than UCs at an AL interface. However, UCs grown at an AL interface with physiological concentration of calcium in medium form only one- to two-layered urothelium of UCs, which are larger and express more differentiation-related proteins uroplakins than UCs in other models. These results demonstrate that the interface itself can play a major, although so-far neglected, role in urothelial physiology, particularly in the formation of the urothelial permeability barrier in vitro and the regulatory mechanisms related with urothelial differentiation. In the study, the culturing of UCs in three successive steps is proposed.

Analysis of Golgi complex function using correlative light-electron microscopy

Though it has been studied for more than 100 years, the Golgi complex remains a fascinating organelle for cell biologists. This is because it is a unique intracellular structure with a list of well-known functions that continues to grow with the discovery of new genes and the development of novel advanced techniques. The Golgi apparatus has been carefully characterized in different organisms, tissues, and cell types both by light and by electron microscopy. However, the new quality step in Golgi research began with the development of correlative light-electron microscopy (CLEM). This innovative method allows visualizing the fate of the same organelle of interest at any moment of its life span first by video imaging in live cells and then by immunoelectron microscopy and 3D reconstruction. Here, we will present the historical overview of different Golgi-associated processes characterized by CLEM and describe the detailed protocol of this complex yet valuable technique.

Freeze-fracture replica immunolabelling reveals urothelial plaques in cultured urothelial cells

The primary function of the urothelium is to provide the tightest and most impermeable barrier in the body, i.e. the blood-urine barrier. Urothelial plaques are formed and inserted into the apical plasma membrane during advanced stages of urothelial cell differentiation. Currently, it is supposed that differentiation with the final formation of urothelial plaques is hindered in cultured urothelial cells. With the aid of the high-resolution imaging technique of freeze-fracture replica immunolabelling, we here provide evidence that urothelial cells in vitro form uroplakin-positive urothelial plaques, localized in fusiform-shaped vesicles and apical plasma membranes. With the establishment of such an in vitro model of urothelial cells with fully developed urothelial plaques and functional properties equivalent to normal bladder urothelium, new perspectives have emerged which challenge prevailing concepts of apical plasma membrane biogenesis and blood-urine barrier development. This may hopefully provide a timely impulse for many ongoing studies and open up new questions for future research.

The Golgi apparatus in the endomembrane-rich gastric parietal cells exist as functional stable mini-stacks dispersed throughout the cytoplasm

Background information. Acid-secreting gastric parietal cells are polarized epithelial cells that harbour highly abundant and specialized, H⁺,K⁺ ATPase-containing, tubulovesicular membranes in the apical cytoplasm. The Golgi apparatus has been implicated in the biogenesis of the tubulovesicular membranes; however, an unanswered question is how a typical Golgi organization could regulate normal membrane transport within the membrane-dense cytoplasm of parietal cells.

Results. Here, we demonstrate that the Golgi apparatus of parietal cells is not the typical juxta-nuclear ribbon of stacks, but rather individual Golgi units are scattered throughout the cytoplasm. The Golgi membrane structures labelled with markers of both cis- and trans-Golgi membrane, indicating the presence of intact Golgi stacks. The parietal cell Golgi stacks were closely aligned with the microtubule network and were shown to participate in both anterograde and retrograde transport pathways. Dispersed Golgi stacks were also observed in parietal cells from H⁺,K⁺ ATPase-deficient mice that lack tubulovesicular membranes.

Conclusions. These results indicate that the unusual organization of individual Golgi stacks dispersed throughout the cytoplasm of these terminally differentiated cells is likely to be a developmentally regulated event.

Hyperplasia as a mechanism for rapid resealing urothelial injuries and maintaining high transepithelial resistance

When the urothelial barrier, i.e., the blood-urine barrier, is injured, rapid resealing of the injury is crucial for the normal functioning of the organism. In order to investigate the mechanisms required for rapid resealing of the barrier, we established in vitro models of hyperplastic and normoplastic urothelia. We found that hyperplastic urothelia achieve significantly higher transepithelial resistance (TER) than normoplastic urothelia. However, the expression of cell junctional (claudin-8, occludin, E-cadherin) and differentiation-related proteins (cytokeratin 20 and uroplakins) is weaker in hyperplastic urothelia. Further investigation of cell differentiation status at the ultrastructural level confirmed that superficial urothelial cells (UCs) in hyperplastic urothelial models achieve a lower differentiation stage than superficial UCs in normoplastic urothelial models. With the establishment of such in vitro models and the aid of TER measurements, flow cytometry, molecular and ultrastructural analysis, we here provide unequivocal evidence that the specific cell-cycle distribution and, consequently, the number of cell layers have a significant influence on the barrier function of urothelia. We demonstrate the importance of hyperplasia for the rapid restoration of the urothelial barrier and the maintenance of high TER until the UCs reach a highly differentiated stage and restoration of the urothelial barrier after injury is complete. The information that this approach provides is unique and we expect that further exploitation of hyperplastic and normoplastic urothelial models in future studies may advance our understanding of blood-urine barrier development and functionality.

Urothelial plaque formation in post-Golgi compartments

Urothelial plaques are specialized membrane domains in urothelial superficial (umbrella) cells, composed of highly ordered uroplakin particles. We investigated membrane compartments involved in the formation of urothelial plaques in mouse umbrella cells. The Golgi apparatus did not contain uroplakins organized into plaques. In the post-Golgi region, three distinct membrane compartments containing uroplakins were characterized: i) Small rounded vesicles, located close to the Golgi apparatus, were labelled weakly with anti-uroplakin antibodies and they possessed no plaques; we termed them "uroplakin-positive transporting vesicles" (UPTVs). ii) Spherical-to-flattened vesicles, termed "immature fusiform vesicles" (iFVs), were uroplakin-positive in their central regions and contained small urothelial plaques. iii) Flattened "mature fusiform vesicles" (mFVs) contained large plaques, which were densely labelled with anti-uroplakin antibodies. Endoytotic marker horseradish peroxidase was not found in these post-Golgi compartments. We propose a detailed model of de novo urothelial plaque formation in post-Golgi compartments: UPTVs carrying individual 16-nm particles detach from the Golgi apparatus and subsequently fuse into iFV. Concentration of 16-nm particles into plaques and removal of uroplakin-negative membranes takes place in iFVs. With additional fusions and buddings, iFVs mature into mFVs, each carrying two urothelial plaques toward the apical surface of the umbrella cell.

Golgi positioning

The Golgi apparatus in mammalian cells is positioned near the centrosome-based microtubule-organizing center (Fig. 1). Secretory cargo moves inward in membrane carriers for delivery to Golgi membranes in which it is processed and packaged for transport outward to the plasma membrane. Cytoplasmic dynein motor proteins (herein termed dynein) primarily mediate inward cargo carrier movement and Golgi positioning. These motors move along microtubules toward microtubule minus-ends embedded in centrosomes. Centripetal motility is controlled by a host of regulators whose precise functions remain to be determined. Significantly, a specific Golgi receptor for dynein has not been identified. This has impaired progress toward elucidation of membrane-motor-microtubule attachment in the periphery and, after inward movement, recycling of the motor for another round. Pericentrosomal positioning of the Golgi apparatus is dynamic. It is regulated during critical cellular processes such as mitosis, differentiation, cell polarization, and cell migration. Positioning is also important as it aligns the Golgi along an axis of cell polarity. In certain cell types, this promotes secretion directed to the proximal plasma membrane domain thereby maintaining specializations critical for diverse processes including wound healing, immunological synapse formation, and axon determination.