Immunoperoxidase methods for the localization of antigens in cultured cells and tissue sections by electron microscopy

Nuclear lipid droplets form in the inner nuclear membrane in a seipin-independent manner

Nuclear lipid droplets (LDs) in hepatocytes are derived from precursors of very-low-density lipoprotein in the ER lumen, but it is not known how cells lacking the lipoprotein secretory function form nuclear LDs. Here, we show that the inner nuclear membrane (INM) of U2OS cells harbors triglyceride synthesis enzymes, including ACSL3, AGPAT2, GPAT3/GPAT4, and DGAT1/DGAT2, and generates nuclear LDs in situ. mTOR inhibition increases nuclear LDs by inducing the nuclear translocation of lipin-1 phosphatidic acid (PA) phosphatase. Seipin, a protein essential for normal cytoplasmic LD formation in the ER, is absent in the INM. Knockdown of seipin increases nuclear LDs and PA in the nucleus, whereas seipin overexpression decreases these. Seipin knockdown also up-regulates lipin-1β expression, and lipin-1 knockdown decreases the effect of seipin knockdown on nuclear LDs without affecting PA redistribution. These results indicate that seipin is not directly involved in nuclear LD formation but instead restrains it by affecting lipin-1 expression and intracellular PA distribution.

Nuclear lipid droplets derive from a lipoprotein precursor and regulate phosphatidylcholine synthesis

The origin and physiological significance of lipid droplets (LDs) in the nucleus is not clear. Here we show that nuclear LDs in hepatocytes are derived from apolipoprotein B (ApoB)-free lumenal LDs, a precursor to very low-density lipoproprotein (VLDL) generated in the ER lumen by microsomal triglyceride transfer protein. ApoB-free lumenal LDs accumulate under ER stress, grow within the lumen of the type I nucleoplasmic reticulum, and turn into nucleoplasmic LDs by disintegration of the surrounding inner nuclear membrane. Oleic acid with or without tunicamycin significantly increases the formation of nucleoplasmic LDs, to which CTP:phosphocholine cytidylyltransferase α (CCTα) is recruited, resulting in activation of phosphatidylcholine (PC) synthesis. Perilipin-3 competes with CCTα in binding to nucleoplasmic LDs, and thus, knockdown and overexpression of perilipin-3 increases and decreases PC synthesis, respectively. The results indicate that nucleoplasmic LDs in hepatocytes constitute a feedback mechanism to regulate PC synthesis in accordance with ER stress.

The origin and physiological significance of lipid droplets (LDs) in the nucleus is not clear. Here authors show that nucleoplasmic LDs in hepatocytes are derived from apolipoprotein B (ApoB)-free lumenal LDs and constitute a feedback mechanism to regulate PC synthesis in accordance with ER stress.

Identification of PSD-95 in the Postsynaptic Density Using MiniSOG and EM Tomography

Combining tomography with electron microscopy (EM) produces images at definition sufficient to visualize individual protein molecules or molecular complexes in intact neurons. When freeze-substituted hippocampal cultures in plastic sections are imaged by EM tomography, detailed structures emerging from 3D reconstructions reveal putative glutamate receptors and membrane-associated filaments containing scaffolding proteins such as postsynaptic density (PSD)-95 family proteins based on their size, shape, and known distributions. In limited instances, structures can be identified with enhanced immuno-Nanogold labeling after light fixation and subsequent freeze-substitution. Molecular identification of structure can be corroborated in their absence after acute protein knockdown or gene knockout. However, additional labeling methods linking EM level structure to molecules in tomograms are needed. A recent development for labeling structures for TEM employs expression of endogenous proteins carrying a green fluorescent tag, miniSOG, to photoconvert diaminobenzidine (DAB) into osmiophilic polymers. This approach requires initial mild chemical fixation but many of structural features in neurons can still be discerned in EM tomograms. The photoreaction product, which appears as electron-dense, fine precipitates decorating protein structures in neurons, may diffuse to fill cytoplasm of spines, thus obscuring specific localization of proteins tagged with miniSOG. Here we develop an approach to minimize molecular diffusion of the DAB photoreaction product in neurons, which allows miniSOG tagged molecule/complexes to be identified in tomograms. The examples reveal electron-dense clusters of reaction product labeling membrane-associated vertical filaments, corresponding to the site of miniSOG fused at the C-terminal end of PSD-95-miniSOG, allowing identification of PSD-95 vertical filaments at the PSD. This approach, which results in considerable improvement in the precision of labeling PSD-95 in tomograms without complications due to the presence of antibody complexes in immunogold labeling, may be applicable for identifying other synaptic proteins in intact neurons.

The Coxiella Burnetii type IVB secretion system (T4BSS) component DotA is released/secreted during infection of host cells and during in vitro growth in a T4BSS-dependent manner

Coxiella burnetii is a Gram-negative intracellular pathogen and is the causative agent of the zoonotic disease Q fever. To cause disease, C. burnetii requires a functional type IVB secretion system (T4BSS) to transfer effector proteins required for the establishment and maintenance of a membrane-bound parasitophorous vacuole (PV) and further modulation of host cell process. However, it is not clear how the T4BSS interacts with the PV membrane since neither a secretion pilus nor an extracellular pore forming apparatus has not been described. To address this, we used the acidified citrate cysteine medium (ACCM) along with cell culture infection and immunological techniques to identify the cellular and extracellular localization of T4BSS components. Interestingly, we found that DotA and IcmX were secreted/released in a T4BSS-dependent manner into the ACCM. Analysis of C. burnetii-infected cell lines revealed that DotA colocalized with the host cell marker CD63 (LAMP3) at the PV membrane. In the absence of bacterial protein synthesis, DotA also became depleted from the PV membrane. These data are the first to identify the release/secretion of C. burnetii T4BSS components during axenic growth and the interaction of a T4BSS component with the PV membrane during infection of host cells.

Visualizing endocytic recycling and trafficking in live neurons by subdiffractional tracking of internalized molecules

Our understanding of endocytic pathway dynamics is restricted by the diffraction limit of light microscopy. Although super-resolution techniques can overcome this issue, highly crowded cellular environments, such as nerve terminals, can also dramatically limit the tracking of multiple endocytic vesicles such as synaptic vesicles (SVs), which in turn restricts the analytical dissection of their discrete diffusional and transport states. We recently introduced a pulse-chase technique for subdiffractional tracking of internalized molecules (sdTIM) that allows the visualization of fluorescently tagged molecules trapped in individual signaling endosomes and SVs in presynapses or axons with 30- to 50-nm localization precision. We originally developed this approach for tracking single molecules of botulinum neurotoxin type A, which undergoes activity-dependent internalization and retrograde transport in autophagosomes. This method was then adapted to localize the signaling endosomes containing cholera toxin subunit-B that undergo retrograde transport in axons and to track SVs in the crowded environment of hippocampal presynapses. We describe (i) the construction of a custom-made microfluidic device that enables control over neuronal orientation; (ii) the 3D printing of a perfusion system for sdTIM experiments performed on glass-bottom dishes; (iii) the dissection, culturing and transfection of hippocampal neurons in microfluidic devices; and (iv) guidance on how to perform the pulse-chase experiments and data analysis. In addition, we describe the use of single-molecule-tracking analytical tools to reveal the average and the heterogeneous single-molecule mobility behaviors. We also discuss alternative reagents and equipment that can, in principle, be used for sdTIM experiments and describe how to adapt sdTIM to image nanocluster formation and/or tubulation in early endosomes during sorting events. The procedures described in this protocol take ∼1 week.

Regulation of post-Golgi LH3 trafficking is essential for collagen homeostasis

Post-translational modifications are necessary for collagen precursor molecules (procollagens) to acquire final shape and function. However, the mechanism and contribution of collagen modifications that occur outside the endoplasmic reticulum and Golgi are not understood. We discovered that VIPAR, with its partner proteins, regulate sorting of lysyl hydroxylase 3 (LH3, also known as PLOD3) into newly identified post-Golgi collagen IV carriers and that VIPAR-dependent sorting is essential for modification of lysines in multiple collagen types. Identification of structural and functional collagen abnormalities in cells and tissues from patients and murine models of the autosomal recessive multisystem disorder Arthrogryposis, Renal dysfunction and Cholestasis syndrome caused by VIPAR and VPS33B deficiencies confirmed our findings. Thus, regulation of post-Golgi LH3 trafficking is essential for collagen homeostasis and for the development and function of multiple organs and tissues.

PML isoform II plays a critical role in nuclear lipid droplet formation

PML-II plays a critical role in generating nuclear lipid droplets, which are associated with promyelocytic leukemia nuclear bodies as well as with the extension of the inner nuclear membrane.

Lipid droplets (LDs) in the nucleus of hepatocyte-derived cell lines were found to be associated with premyelocytic leukemia (PML) nuclear bodies (NBs) and type I nucleoplasmic reticulum (NR) or the extension of the inner nuclear membrane. Knockdown of PML isoform II (PML-II) caused a significant decrease in both nuclear LDs and type I NR, whereas overexpression of PML-II increased both. Notably, these effects were evident only in limited types of cells, in which a moderate number of nuclear LDs exist intrinsically, and PML-II was targeted not only at PML NBs, but also at the nuclear envelope, excluding lamins and SUN proteins. Knockdown of SUN proteins induced a significant increase in the type I NR and nuclear LDs, but these effects were cancelled by simultaneous knockdown of PML-II. Nuclear LDs harbored diacylglycerol O-acyltransferase 2 and CTP:phosphocholine cytidylyltransferase α and incorporated newly synthesized lipid esters. These results corroborated that PML-II plays a critical role in generating nuclear LDs in specific cell types.

C. pneumoniae disrupts eNOS trafficking and impairs NO production in human aortic endothelial cells

Endothelial nitric oxide synthase (eNOS) generated NO plays a crucial physiological role in the regulation of vascular tone. eNOS is a constitutively expressed synthase whose enzymatic function is regulated by dual acylation, phosphorylation, protein-protein interaction and subcellular localization. In endothelial cells, the enzyme is primarily localized to the Golgi apparatus (GA) and the plasma membrane where it binds to caveolin-1. Upon stimulation, the enzyme is translocated from the plasma membrane to the cytoplasm where it generates NO. When activation of eNOS ceases, the majority of the enzyme is recycled back to the membrane fraction. An inability of eNOS to cycle between the cytosol and the membrane leads to impaired NO production and vascular dysfunction. Chlamydia pneumoniae is a Gram-negative obligate intracellular bacterium that primarily infects epithelial cells of the human respiratory tract, but unlike any other chlamydial species, C. pneumoniae displays tropism toward atherosclerotic tissues. In this study, we demonstrate that C. pneumoniae inclusions colocalize with eNOS, and the microorganism interferes with trafficking of the enzyme from the GA to the plasma membrane in primary human aortic endothelial cells. This mislocation of eNOS results in significant inhibition of NO release by C. pneumoniae-infected cells. Furthermore, we show that the distribution of eNOS in C. pneumoniae-infected cells is altered due to an intimate association of the Golgi complex with chlamydial inclusions rather than by direct interaction of the enzyme with the chlamydial inclusion membrane.

Secreted Frizzled-related protein 1 (sFRP1) regulates spermatid adhesion in the testis via dephosphorylation of focal adhesion kinase and the nectin-3 adhesion protein complex

Development of spermatozoa in adult mammalian testis during spermatogenesis involves extensive cell migration and differentiation. Spermatogonia that reside at the basal compartment of the seminiferous epithelium differentiate into more advanced germ cell types that migrate toward the apical compartment until elongated spermatids are released into the tubule lumen during spermiation. Apical ectoplasmic specialization (ES; a testis-specific anchoring junction) is the only cell junction that anchors and maintains the polarity of elongating/elongated spermatids (step 8-19 spermatids) in the epithelium. Little is known regarding the signaling pathways that trigger the disassembly of the apical ES at spermiation. Here, we show that secreted Frizzled-related protein 1 (sFRP1), a putative tumor suppressor gene that is frequently down-regulated in multiple carcinomas, is a crucial regulatory protein for spermiation. The expression of sFRP1 is tightly regulated in adult rat testis to control spermatid adhesion and sperm release at spermiation. Down-regulation of sFRP1 during testicular development was found to coincide with the onset of the first wave of spermiation at approximately age 45 d postpartum, implying that sFRP1 might be correlated with elongated spermatid adhesion conferred by the apical ES before spermiation. Indeed, administration of sFRP1 recombinant protein to the testis in vivo delayed spermiation, which was accompanied by down-regulation of phosphorylated (p)-focal adhesion kinase (FAK)-Tyr(397) and retention of nectin-3 adhesion protein at the apical ES. To further investigate the functional relationship between p-FAK-Tyr(397) and localization of nectin-3, we overexpressed sFRP1 using lentiviral vectors in the Sertoli-germ cell coculture system. Consistent with the in vivo findings, overexpression of sFRP1 induced down-regulation of p-FAK-Tyr(397), leading to a decline in phosphorylation of nectin-3. In summary, this report highlights the critical role of sFRP1 in regulating spermiation via its effects on the FAK signaling and retention of nectin-3 adhesion complex at the apical ES.

Scanning electron microscopy

Scanning electron microscopy (SEM) remains distinct in its ability to allow topographical visualization of structures. Key elements to consider for successful examination of biological specimens include appropriate preparative and imaging techniques. Chemical processing induces structural artifacts during specimen preparation, and several factors need to be considered when selecting fixation protocols to reduce these effects while retaining structures of interest. Particular care for proper dehydration of specimens is essential to minimize shrinkage and is necessary for placement under the high-vacuum environment required for routine operation of standard SEMs. Choice of substrate for mounting and coating specimens can reduce artifacts known as charging, and a basic understanding of microscope settings can optimize parameters to achieve desired results. This unit describes fundamental techniques and tips for routine specimen preparation for a variety of biological specimens, preservation of labile or fragile structures, immune-labeling strategies, and microscope imaging parameters for optimal examination by SEM.

Compensatory endocytosis in bladder umbrella cells occurs through an integrin-regulated and RhoA- and dynamin-dependent pathway

Compensatory endocytosis (CE) ensures recycling of membrane components and maintenance of plasma membrane size; however, the mechanisms, regulation, and physiological functions of clathrin-independent modes of CE are poorly understood. CE was studied in umbrella cells, which undergo regulated exocytosis of subapical discoidal/fusiform vesicles (DFV) during bladder filling, and may then replenish the pool of DFV by internalizing apical membrane during voiding. We found that voiding-stimulated CE, which depended on beta(1) integrin-associated signalling pathways, occurred by a dynamin-, actin-, and RhoA-regulated mechanism and was independent of caveolins, clathrin, and flotillin. Internalized apical membrane and fluid were initially found in ZO-1-positive vesicles, which were distinct from DFV, classical early endosomes, or the Golgi, and subsequently in lysosomes. We conclude that clathrin-independent CE in umbrella cells functions to recover membrane during voiding, is integrin regulated, occurs by a RhoA- and dynamin-dependent pathway, and terminates in degradation and not recapture of membrane in DFV.

Correlative microscopy: a potent tool for the study of rare or unique cellular and tissue events

Biological studies have relied on two complementary microscope technologies - light (fluorescence) microscopy and electron microscopy. Light microscopy is used to study phenomena at a global scale to look for unique or rare events, and it also provides an opportunity for live imaging, whereas the forte of electron microscopy is the high resolution. Traditionally light and electron microscopy observations are carried out in different populations of cells/tissues and a 'correlative' inference is drawn. The advent of true correlative light-electron microscopy has allowed high-resolution imaging by electron microscopy of the same structure observed by light microscopy, and in advanced cases by video microscopy. Thus a rare event captured by low-resolution imaging of a population or transient events captured by live imaging can now also be studied at high resolution by electron microscopy. Here, the potential and difficulties of this approach, along with the most impressive breakthroughs obtained by these methods, are discussed.

Disruption of the blood-testis barrier integrity by bisphenol A in vitro: is this a suitable model for studying blood-testis barrier dynamics?

Bisphenol A, an estrogenic environmental toxicant, has been implicated to have hazardous effects on reproductive health in humans and rodents. However, there are conflicting reports in the literature regarding its effects on male reproductive function. In this study, it was shown that in adult rats treated with acute doses of bisphenol A, a small but statistically insignificant percentage of seminiferous tubules in the testes displayed signs of germ cell loss, consistent with some earlier reports. It also failed to disrupt the blood-testis barrier in vivo. This is possibly due to the low bioavailability of free bisphenol A in the systemic circulation. However, bisphenol A disrupted the blood-testis barrier when administered to immature 20-day-old rats, consistent with earlier reports concerning the higher susceptibility of immature rats towards bisphenol A. This observation was confirmed using primary Sertoli cells cultured in vitro with established tight junction-permeability barrier that mimicked the blood-testis barrier in vivo. The reversible disruption of Sertoli cell tight junction barrier by bisphenol A was associated with an activation of ERK, and a decline in the levels of selected proteins at the tight junction, basal ectoplasmic specialization, and gap junction at the blood-testis barrier. Studies by dual-labeled immunofluorescence analysis and biotinylation techniques also illustrated declining levels of occludin, connexin 43, and N-cadherin at the cell-cell interface following bisphenol A treatment. In summary, bisphenol A reversibly perturbs the integrity of the blood-testis barrier in Sertoli cells in vitro, which can also serve as a suitable model for studying the dynamics of the blood-testis barrier.

NMDA receptor phosphorylation at a site affected in schizophrenia controls synaptic and behavioral plasticity

Phosphorylation of the NR1 subunit of NMDA receptors (NMDARs) at serine (S) 897 is markedly reduced in schizophrenia patients. However, the role of NR1 S897 phosphorylation in normal synaptic function and adaptive behaviors are unknown. To address these questions, we generated mice in which the NR1 S897 is replaced with alanine (A). This knock-in mutation causes severe impairment in NMDAR synaptic incorporation and NMDAR-mediated synaptic transmission. Furthermore, the phosphomutant animals have reduced AMPA receptor (AMPAR)-mediated synaptic transmission, decreased AMPAR GluR1 subunit in the synapse, and impaired long-term potentiation. Finally, the mutant mice exhibit behavioral deficits in social interaction and sensorimotor gating. Our results suggest that an impairment in NR1 phosphorylation leads to glutamatergic hypofunction that can contribute to behavioral deficits associated with psychiatric disorders.

Correlative video light/electron microscopy

This unit describes newly developed methods that allow the examination of living cells by time-lapse analysis with the subsequent identification of the just-observed organelle under an electron microscope. To understand how such cellular functions, such as intracellular traffic, cytokinesis, and cell migration, are organized and executed in vivo, it is most useful to observe living cells in real time with the spatial resolution afforded by electron microscopy (EM). Most suitable for this is a conceptually simple, yet powerful, method called correlative video light/electron microscopy (CVLEM), by which observations of the in vivo dynamics and the ultrastructure of intracellular objects can indeed be combined to achieve the above-mentioned result. This unit describes this methodology, illustrates the type of questions that the CVLEM approach was designed to address, and discusses the expertise required for successful application of the technique.

Antigen discovery: A postgenomic approach to paratuberculosis diagnosis

Paratuberculosis is a chronic enteritis caused in domestic and wild ruminant species by Mycobacterium avium subsp. paratuberculosis (MAP) that is responsible for major economic losses to the agricultural industry. To date, no satisfactory therapeutic, vaccine, or diagnostic tools are available, globally impairing all control programs. In this study, we have undertaken a large-scale postgenomic analysis of MAP proteins, to identify specific antigens that could potentially improve the diagnosis of paratuberculosis. Two complementary approaches were implemented, the first one consisting in the systematic proteomic identification of proteins present in MAP culture filtrates (CFs), followed by the selection of MAP-specific proteins by BLAST query on available mycobacterial genomes. The resulting database represents the first established secretome of MAP and a useful source of potentially specific antigens. The second approach consisted in the immunoproteomic analysis of both MAP extracts and CFs, using sera from MAP-infected and uninfected cattle. Combining results obtained with both approaches resulted in the identification of 25 candidate diagnostic antigens. Five of these were tested in an ELISA assay for their diagnostic potential, on a limited panel of field sera, and the combination of three of them competed in performance with available commercial assays, reaching a test sensitivity of 94.74% and specificity of 97.92%.

Aggregated myocilin induces russell bodies and causes apoptosis: implications for the pathogenesis of myocilin-caused primary open-angle glaucoma

Primary open-angle glaucoma with elevated intraocular pressure is a leading cause of blindness worldwide. Mutations of myocilin are known to play a critical role in the manifestation of the disease. Misfolded mutant myocilin forms secretion-incompetent intracellular aggregates. The block of myocilin secretion was proposed to alter the extracellular matrix environment of the trabecular meshwork, with subsequent impediment of aqueous humor outflow leading to elevated intraocular pressure. However, the molecular pathogenesis of myocilin-caused glaucoma is poorly defined. In this study, we show that heteromeric complexes composed of wild-type and mutant myocilin were retained in the rough endoplasmic reticulum, aggregating to form inclusion bodies typical of Russell bodies. The presence of myocilin aggregates induced the unfolded protein response proteins BiP and phosphorylated endoplasmic reticulum-localized eukaryotic initiation factor-2alpha kinase (PERK) with the subsequent activation of caspases 12 and 3 and expression of C/EBP homologous protein (CHOP)/GADD153, leading to apoptosis. Our findings identify endoplasmic reticulum stress-induced apoptosis as a pathway to explain the reduction of trabecular meshwork cells in patients with myocilin-caused glaucoma. As a consequence, the phagocytotic capacity of the remaining trabecular meshwork cell population would be insufficient for effective cleaning of aqueous humor, constituting a major pathogenetic factor for the development of increased intraocular pressure in primary open-angle glaucoma.

A highly sensitive and subspecies-specific surface antigen enzyme- linked immunosorbent assay for diagnosis of Johne's disease

Johne's disease (JD), or paratuberculosis, caused by Mycobacterium avium subsp. paratuberculosis, is one of the most widespread and economically important diseases of livestock and wild ruminants worldwide. Control of JD could be accomplished by diagnosis and good animal husbandry, but this is currently not feasible because commercially available diagnostic tests have low sensitivity levels and are incapable of diagnosing prepatent infections. In this study, a highly sensitive and subspecies-specific enzyme-linked immunosorbent assay was developed for the diagnosis of JD by using antigens extracted from the surface of M. avium subsp. paratuberculosis. Nine different chemicals and various intervals of agitation by vortex were evaluated for their ability to extract the surface antigens. Various quantities of surface antigens per well in a 96-well microtiter plate were also tested. The greatest differences in distinguishing between JD-positive and JD-negative serum samples by ethanol vortex enzyme-linked immunosorbent assay (EVELISA) were obtained with surface antigens dislodged from 50 microg/well of bacilli treated with 80% ethanol followed by a 30-second interval of agitation by vortex. The diagnostic specificity and sensitivity of the EVELISA were 97.4% and 100%, respectively. EVELISA plates that had been vacuum-sealed and then tested 7 weeks later (the longest interval tested) had diagnostic specificity and sensitivity rates of 96.9 and 100%, respectively. In a comparative study involving serum samples from 64 fecal culture-positive cattle, the EVELISA identified 96.6% of the low-level fecal shedders and 100% of the midlevel and high-level shedders, whereas the Biocor ELISA detected 13.7% of the low-level shedders, 25% of the mid-level shedders, and 96.2% of the high-level shedders. Thus, the EVELISA was substantially superior to the Biocor ELISA, especially in detecting low-level and midlevel shedders. The EVELISA may form the basis for a highly sensitive and subspecies-specific test for the diagnosis of JD.

A novel enzyme-linked immunosorbent assay for diagnosis of Mycobacterium avium subsp. paratuberculosis infections (Johne's Disease) in cattle

Enzyme-linked immunosorbent assays (ELISAs) for the diagnosis of Johne's disease (JD), caused by Mycobacterium avium subsp. paratuberculosis, were developed using whole bacilli treated with formaldehyde (called WELISA) or surface antigens obtained by treatment of M. avium subsp. paratuberculosis bacilli with formaldehyde and then brief sonication (called SELISA). ELISA plates were coated with either whole bacilli or sonicated antigens and tested for reactivity against serum obtained from JD-positive and JD-negative cattle or from calves experimentally inoculated with M. avium subsp. paratuberculosis, Mycobacterium avium subsp. avium, or Mycobacterium bovis. Because the initial results obtained from the WELISA and SELISA were similar, most of the subsequent experiments reported herein were performed using the SELISA method. To optimize the SELISA test, various concentrations (3.7 to 37%) of formaldehyde and intervals of sonication (2 to 300 s) were tested. With an increase in formaldehyde concentration and a decreased interval of sonication, there was a concomitant decrease in nonspecific binding by the SELISA. SELISAs prepared by treating M. avium subsp. paratuberculosis with 37% formaldehyde and then a 2-s burst of sonication produced the greatest difference (7x) between M. avium subsp. paratuberculosis-negative and M. avium subsp. paratuberculosis-positive serum samples. The diagnostic sensitivity and specificity for JD by the SELISA were greater than 95%. The SELISA showed subspecies-specific detection of M. avium subsp. paratuberculosis infections in calves experimentally inoculated with M. avium subsp. paratuberculosis or other mycobacteria. Based on diagnostic sensitivity and specificity, the SELISA appears superior to the commercial ELISAs routinely used for the diagnosis of JD.

Degradation of Chlamydia pneumoniae by peripheral blood monocytic cells

Chlamydia pneumoniae is a common human respiratory pathogen that has been associated with a variety of chronic diseases, including atherosclerosis. The role of this organism in the pathogenesis of atherosclerosis remains unknown. A key question is how C. pneumoniae is transferred from the site of primary infection to a developing atherosclerotic plaque. It has been suggested that circulating monocytes could be vehicles for dissemination of C. pneumoniae since the organism has been detected in peripheral blood monocytic cells (PBMCs). In this study we focused on survival of C. pneumoniae within PBMCs isolated from the blood of healthy human donors. We found that C. pneumoniae does not grow and multiply in cultured primary monocytes. In C. pneumoniae-infected monocyte-derived macrophages, growth of the organism was very limited, and the majority of the bacteria were eradicated. We also found that the destruction of C. pneumoniae within infected macrophages resulted in a gradual diminution of chlamydial antigens, although some of these antigens could be detected for days after the initial infection. The detected antigens present in infected monocytes and monocyte-derived macrophages represented neither chlamydial inclusions nor intact organisms. The use of {N-[7-(4-nitrobenzo-2-oxa-1,3-diazole)]}-6-aminocaproyl-d-erythro-sphingosine as a vital stain for chlamydiae proved to be a sensitive method for identifying rare C. pneumoniae inclusions and was useful in the detection of even aberrant developmental forms.

Localization of plasma membrane t-SNAREs syntaxin 2 and 3 in intracellular compartments

BACKGROUND

Membrane fusion requires the formation of a complex between a vesicle protein (v-SNARE) and the target membrane proteins (t-SNAREs). Syntaxin 2 and 3 are t-SNAREs that, according to previous over-expression studies, are predominantly localized at the plasma membrane. In the present study we investigated localization of the endogenous syntaxin 2 and 3.

RESULTS

Endogenous syntaxin 2 and 3 were found in NRK cells in intracellular vesicular structures in addition to regions of the plasma membrane. Treatment of these cells with N-ethylmaleimide (NEM), which is known to inactivate membrane fusion, caused syntaxin 3 to accumulate in the trans-Golgi network and syntaxin 2 in perinuclear membrane vesicles. Kinetic analysis in the presence of NEM indicated that this redistribution of syntaxin 2 and 3 takes place via actin containing structures.

CONCLUSION

Our data suggest that syntaxin 2 cycles between the plasma membrane and the perinuclear compartment whereas syntaxin 3 cycles between the plasma membrane and the trans-Golgi network. It is possible that this cycling has an important role in the regulation of t-SNARE function.

Dicumarol, an inhibitor of ADP-ribosylation of CtBP3/BARS, fragments golgi non-compact tubular zones and inhibits intra-golgi transport

Dicumarol (3,3'-methylenebis[4-hydroxycoumarin]) is an inhibitor of brefeldin-A-dependent ADP-ribosylation that antagonises brefeldin-A-dependent Golgi tubulation and redistribution to the endoplasmic reticulum. We have investigated whether dicumarol can directly affect the morphology of the Golgi apparatus. Here we show that dicumarol induces the breakdown of the tubular reticular networks that interconnect adjacent Golgi stacks and that contain either soluble or membrane-associated cargo proteins. This results in the formation of 65-120-nm vesicles that are sometimes invaginated. In contrast, smaller vesicles (45-65 nm in diameter, a size consistent with that of coat-protein-I-dependent vesicles) that excluded cargo proteins from their lumen are not affected by dicumarol. All other endomembranes are largely unaffected by dicumarol, including Golgi stacks, the ER, multivesicular bodies and the trans-Golgi network. In permeabilized cells, dicumarol activity depends on the function of CtBP3/BARS protein and pre-ADP-ribosylation of cytosol inhibits the breakdown of Golgi tubules by dicumarol. In functional experiments, dicumarol markedly slows down intra-Golgi traffic of VSV-G transport from the endoplasmic reticulum to the medial Golgi, and inhibits the diffusional mobility of both galactosyl transferase and VSV-G tagged with green fluorescent protein. However, it does not affect: transport from the trans-Golgi network to the cell surface; Golgi-to-endoplasmic reticulum traffic of ERGIC58; coat-protein-I-dependent Golgi vesiculation by AlF4 or ADP-ribosylation factor; or ADP-ribosylation factor and beta-coat protein binding to Golgi membranes. Thus the ADP-ribosylation inhibitor dicumarol induces the selective breakdown of the tubular components of the Golgi complex and inhibition of intra-Golgi transport. This suggests that lateral diffusion between adjacent stacks has a role in protein transport through the Golgi complex.

Visualizing intracellular events in vivo by combined video fluorescence and 3-D electron microscopy

The combination of the capability of in vivo fluorescence video microscopy with the power of resolution of electron microscopy (EM) has been described. This approach is based on such an association of two techniques. An individual intracellular structure can be monitored in vivo, typically through the use of markers fused with green fluorescent protein (GFP), and a "snapshot" of its three-dimensional (3-D) ultrastructure and especially tomographic reconstruction can then be taken at any chosen time during its life cycle. The pitfalls and potential of this approach are discussed.

Golgi enzymes are enriched in perforated zones of golgi cisternae but are depleted in COPI vesicles

In the most widely accepted version of the cisternal maturation/progression model of intra-Golgi transport, the polarity of the Golgi complex is maintained by retrograde transport of Golgi enzymes in COPI-coated vesicles. By analyzing enzyme localization in relation to the three-dimensional ultrastructure of the Golgi complex, we now observe that Golgi enzymes are depleted in COPI-coated buds and 50- to 60-nm COPI-dependent vesicles in a variety of different cell types. Instead, we find that Golgi enzymes are concentrated in the perforated zones of cisternal rims both in vivo and in a cell-free system. This lateral segregation of Golgi enzymes is detectable in some stacks during steady-state transport, but it was significantly prominent after blocking endoplasmic reticulum-to-Golgi transport. Delivery of transport carriers to the Golgi after the release of a transport block leads to a diminution in Golgi enzyme concentrations in perforated zones of cisternae. The exclusion of Golgi enzymes from COPI vesicles and their transport-dependent accumulation in perforated zones argues against the current vesicle-mediated version of the cisternal maturation/progression model.

Active and specific recruitment of a soluble cargo protein for endoplasmic reticulum exit in the absence of functional COPII component Sec24p

Exit of proteins from the yeast endoplasmic reticulum (ER) is thought to occur in vesicles coated by four proteins, Sec13p, Sec31p, Sec23p and Sec24p, which assemble at ER exit sites to form the COPII coat. Sec13p may serve a structural function, whereas Sec24p has been suggested to operate in selection of cargo proteins into COPII vesicles. We showed recently that the soluble glycoprotein Hsp150 exited the ER in the absence of Sec13p function. Here we show that its ER exit did not require functional Sec24p. Hsp150 was secreted to the medium in a sec24-1 mutant at restrictive temperature 37 degrees C, while cell wall invertase and vacuolar carboxypeptidase Y remained in the ER. The determinant guiding Hsp150 to this transport route was mapped to the C-terminal domain of 114 amino acids by deletion analysis, and by an HRP fusion protein-based EM technology adapted here for yeast. This domain actively mediated ER exit of Sec24p-dependent invertase in the absence of Sec24p function. However, the domain was entirely dispensable for ER exit when Sec24p was functional. The Sec24p homolog Sfb2p was shown not to compensate for nonfunctional Sec24p in ER exit of Hsp150. Our data show that a soluble cargo protein, Hsp150, is selected actively and specifically to budding sites lacking normal Sec24p by a signature residing in its C-terminal domain.

Release of canine parvovirus from endocytic vesicles

Canine parvovirus (CPV) is a small nonenveloped virus with a single-stranded DNA genome. CPV enters cells by clathrin-mediated endocytosis and requires an acidic endosomal step for productive infection. Virion contains a potential nuclear localization signal as well as a phospholipase A(2) like domain in N-terminus of VP1. In this study we characterized the role of PLA(2) activity on CPV entry process. PLA(2) activity of CPV capsids was triggered in vitro by heat or acidic pH. PLA(2) inhibitors inhibited the viral proliferation suggesting that PLA(2) activity is needed for productive infection. The N-terminus of VP1 was exposed during the entry, suggesting that PLA(2) activity might have a role during endocytic entry. The presence of drugs modifying endocytosis (amiloride, bafilomycin A(1), brefeldin A, and monensin) caused viral proteins to remain in endosomal/lysosomal vesicles, even though the drugs were not able to inhibit the exposure of VP1 N-terminal end. These results indicate that the exposure of N-terminus of VP1 alone is not sufficient to allow CPV to proliferate. Some other pH-dependent changes are needed for productive infection. In addition to blocking endocytic entry, amiloride was able to block some postendocytic steps. The ability of CPV to permeabilize endosomal membranes was demonstrated by feeding cells with differently sized rhodamine-conjugated dextrans together with the CPV in the presence or in the absence of amiloride, bafilomycin A(1), brefeldin A, or monensin. Dextran with a molecular weight of 3000 was released from vesicles after 8 h of infection, while dextran with a molecular weight of 10,000 was mainly retained in vesicles. The results suggest that CPV infection does not cause disruption of endosomal vesicles. However, the permeability of endosomal membranes apparently changes during CPV infection, probably due to the PLA(2) activity of the virus. These results suggest that parvoviral PLA(2) activity is essential for productive infection and presumably utilized in membrane penetration process of the virus, but CPV also needs other pH-dependent changes or factors to be released to the cytoplasm from endocytic vesicles.

Exploitation of microtubule cytoskeleton and dynein during parvoviral traffic toward the nucleus

Canine parvovirus (CPV), a model virus for the study of parvoviral entry, enters host cells by receptor-mediated endocytosis, escapes from endosomal vesicles to the cytosol, and then replicates in the nucleus. We examined the role of the microtubule (MT)-mediated cytoplasmic trafficking of viral particles toward the nucleus. Immunofluorescence and immunoelectron microscopy showed that capsids were transported through the cytoplasm into the nucleus after cytoplasmic microinjection but that in the presence of MT-depolymerizing agents, viral capsids were unable to reach the nucleus. The nuclear accumulation of capsids was also reduced by microinjection of an anti-dynein antibody. Moreover, electron microscopy and light microscopy experiments demonstrated that viral capsids associate with tubulin and dynein in vitro. Coprecipitation studies indicated that viral capsids interact with dynein. When the cytoplasmic transport process was studied in living cells by microinjecting fluorescently labeled capsids into the cytoplasm of cells containing fluorescent tubulin, capsids were found in close contact with MTs. These results suggest that intact MTs and the motor protein dynein are required for the cytoplasmic transport of CPV capsids and contribute to the accumulation of the capsid in the nucleus.

A missense mutation (G1506E) in the adhesion G domain of laminin-5 causes mild junctional epidermolysis bullosa

Laminin-5 is the major adhesion ligand for epithelial cells. Mutations in the genes encoding laminin-5 cause junctional epidermolysis bullosa (JEB), a recessive inherited disease characterized by extensive epithelial-mesenchymal disadhesion. We describe a JEB patient compound heterozygote for two novel mutations in the gene (LAMA3) encoding the laminin alpha3 chain. The maternal mutation (1644delG) generates mRNA transcripts that undergo nonsense-mediated decay. The paternal mutation results in the Gly1506-->Glu substitution (G1506E) within the C-terminal globular region of the alpha3 chain (G domain). Mutation G1506E affects the proper folding of the fourth module of the G domain and results in the retention of most of the mutated polypeptide within the endoplasmic reticulum (ER). However, scant amounts of the mutated laminin-5 are secreted, undergo physiologic extracellular maturation, and correctly localize within the cutaneous basement membrane zone in patient's skin. Our findings represent the first demonstration of an ER-retained mutant laminin-5 leading to a mild JEB phenotype.

Regulation of Sertoli cell tight junction dynamics in the rat testis via the nitric oxide synthase/soluble guanylate cyclase/3',5'-cyclic guanosine monophosphate/protein kinase G signaling pathway: an in vitro study

Nitric oxide (NO) synthase (NOS) catalyzes the oxidation of L-arginine to NO. NO plays a crucial role in regulating various physiological functions, possibly including junction dynamics via its effects on cAMP and cGMP, which are known modulators of tight junction (TJ) dynamics. Although inducible NOS (iNOS) and endothelial NOS (eNOS) are found in the testis and have been implicated in the regulation of spermatogenesis, their role(s) in TJ dynamics, if any, is not known. When Sertoli cells were cultured at 0.5-1.2 x 10(6) cells/cm(2) on Matrigel-coated dishes or bicameral units, functional TJ barrier was formed when the barrier function was assessed by quantifying transepithelial electrical resistance across the cell epithelium. The assembly of the TJ barrier was shown to associate with a significant plummeting in the levels of iNOS and eNOS, seemingly suggesting that their presence by producing NO might perturb TJ assembly. To further confirm the role of NOS on the TJ barrier function in vitro, zinc (II) protoporphyrin-IX (ZnPP), an NOS inhibitor and a soluble guanylate cyclase inhibitor, was added to the Sertoli cell cultures during TJ assembly. Indeed, ZnPP was found to facilitate the assembly and maintenance of the Sertoli cell TJ barrier, possibly by inducing the production of TJ-associated proteins, such as occludin. Subsequent studies by immunoprecipitation and immunoblotting have shown that iNOS and eNOS are structurally linked to TJ-integral membrane proteins, such as occludin, and cytoskeletal proteins, such as actin, vimentin, and alpha-tubulin. When the cAMP and cGMP levels in these ZnPP-treated samples were quantified, a ZnPP-induced reduction of intracellular cGMP, but not cAMP, was indeed detected. Furthermore, 8-bromo-cGMP, a cell membrane-permeable analog of cGMP, could also perturb the TJ barrier dose dependently similar to the effects of 8-bromo-cAMP. KT-5823, a specific inhibitor of protein kinase G, was shown to facilitate the Sertoli cell TJ barrier assembly. Cytokines, such as TGF-beta and TNF-alpha, known to perturb the Sertoli cell TJ barrier, were also shown to stimulate Sertoli cell iNOS and eNOS expression dose dependently in vitro. Collectively, these results illustrate NOS is an important physiological regulator of TJ dynamics in the testis, exerting its effects via the NO/soluble guanylate cyclase/cGMP/protein kinase G signaling pathway.

Palmitoylation regulates regulators of G-protein signaling (RGS) 16 function. I. Mutation of amino-terminal cysteine residues on RGS16 prevents its targeting to lipid rafts and palmitoylation of an internal cysteine residue

Regulators of G-protein signaling (RGS) proteins down-regulate signaling by heterotrimeric G-proteins by accelerating GTP hydrolysis on the G alpha subunits. Palmitoylation, the reversible addition of palmitate to cysteine residues, occurs on several RGS proteins and is critical for their activity. For RGS16, mutation of Cys-2 and Cys-12 blocks its incorporation of [3H]palmitate and ability to turn-off Gi and Gq signaling and significantly inhibited its GTPase activating protein activity toward aG alpha subunit fused to the 5-hydroxytryptamine receptor 1A, but did not reduce its plasma membrane localization based on cell fractionation studies and immunoelectron microscopy. Palmitoylation can target proteins, including many signaling proteins, to membrane microdomains, called lipid rafts. A subpopulation of endogenous RGS16 in rat liver membranes and overexpressed RGS16 in COS cells, but not the nonpalmitoylated cysteine mutant of RGS16, localized to lipid rafts. However, disruption of lipid rafts by treatment with methyl-beta-cyclodextrin did not decrease the GTPase activating protein activity of RGS16. The lipid raft fractions were enriched in protein acyltransferase activity, and RGS16 incorporated [3H]palmitate into a peptide fragment containing Cys-98, a highly conserved cysteine within the RGS box. These results suggest that the amino-terminal palmitoylation of an RGS protein promotes its lipid raft targeting that allows palmitoylation of a poorly accessible cysteine residue that we show in the accompanying article (Osterhout, J. L., Waheed, A. A., Hiol, A., Ward, R. J., Davey, P. C., Nini, L., Wang, J., Milligan, G., Jones, T. L. Z., and Druey, K. M. (2003) J. Biol. Chem. 278, 19309-19316) was critical for RGS16 and RGS4 GAP activity.

Osteoclast ruffled border has distinct subdomains for secretion and degraded matrix uptake

Subosteoclastic bone resorption is a result of HCl and proteinase secretion through a late endosome-like bone facing membrane domain called ruffled border. As bone matrix is degraded, it enters osteoclasts' transcytotic vesicles for further processing and is then finally exocytosed to the intercellular space. The present study clarifies the spatial relationship between these vesicle fusion and matrix uptake processes at the ruffled border. Our results show the presence of vacuolar H+-ATPase, small GTPase rab7 as well as dense aggregates of F-actin at the peripheral ruffled border, where basolaterally endocytosed transferrin and cathepsin K are delivered. On the contrary, rhodamine-labeled bone matrix enters transcytotic vesicles at the central ruffled border, where the vesicle budding proteins such as clathrin, AP-2 and dynamin II are also localized. We present a model for the mechanism of ruffled border turnover and suggest that, due to its late endosomal characteristics, the ruffled border serves as a valuable model for studying the dynamic organization of other endosomal compartments as well.

Restricted fusion of Chlamydia trachomatis vesicles with endocytic compartments during the initial stages of infection

The chlamydial inclusion occupies a unique niche within the eukaryotic cell that does not interact with endocytic compartments but instead is fusogenic with a subset of sphingomyelin-containing exocytic vesicles. The Chlamydia trachomatis inclusion acquires these distinctive properties by as early as 2 h postinfection as demonstrated by the ability to acquire sphingomyelin, endogenously synthesized from 6[N-[(7-nitrobenzo-2-oxa-1,3-diazol-4-yl)amino]caproylsphingosine] (C(6)-NBD-ceramide). The molecular mechanisms involved in transformation of the properties and cellular interactions of the inclusion are unknown except that they require early chlamydial transcription and translation. Although the properties of the inclusion are established by 2 h postinfection, the degree of interaction with endocytic pathways during the brief interval before fusogenicity with an exocytic pathway is established is unknown. Using a combination of confocal and electron microscopy to localize endocytic and lysosomal markers in C. trachomatis infected cells during the early stages of infection, we demonstrate a lack of these markers within the inclusion membrane or lumen of the inclusion to conclude that the nascent chlamydial inclusion is minimally interactive with endosomal compartments during this interval early in infection. Even when prevented from modifying the properties of the inclusion by incubation in the presence of protein synthesis inhibitors, vesicles containing elementary bodies are very slow to acquire lysosomal characteristics. These results imply a two-stage mechanism for chlamydial avoidance of lysosomal fusion: (i) an initial phase of delayed maturation to lysosomes due to an intrinsic property of elementary bodies and (ii) an active modification of the vesicular interactions of the inclusion requiring chlamydial protein synthesis.

Endogenous plasma membrane t-SNARE syntaxin 4 is present in rab11 positive endosomal membranes and associates with cortical actin cytoskeleton

Membrane fusion requires the formation of a complex between a vesicle protein (v-SNARE) and the target membrane proteins (t-SNAREs). Syntaxin 4 is a t-SNARE that, according to previous overexpression studies, is predominantly localized at the plasma membrane. In the present study endogenous syntaxin 4 was found in intracellular vesicular structures in addition to regions of the plasma membrane. In these vesicular structures syntaxin 4 colocalized with rab11, a marker of recycling endosomes. Furthermore, syntaxin 4 colocalized with actin at the dynamic regions of the plasma membrane. Treatment with N-ethylmaleimide, the membrane transport inhibitor, caused an increased accumulation of syntaxin 4/rab11 positive vesicles in actin filament-like structures. Finally, purified recombinant syntaxin 4 but not syntaxin 2 or 3 cosedimented with actin filaments in vitro, suggesting direct interaction between these two proteins. Taken together, these data suggest that syntaxin 4 regulates secretion at the actin-rich areas of the plasma membrane and may be recycled through rab11 positive intracellular membranes.

The beta1 integrin subunit is not a specific component of the costamere domain in human myocardial cells

Studies on altered integrin receptor expression during cardiac hypertrophy and heart failure requires accurate knowledge of the distributional pattern of integrins in myocardial cells. At present the general consensus is that in cardiac muscle the beta1 integrin receptor is mainly localized to the same sarcolemmal domain as vinculin at Z-band levels ('costamere'). Since most previous studies have been focusing on myocardial integrin distribution in lower mammals, the myocardial localization of the beta1 integrin subunit was investigated in biopsies collected from the auricle of patients undergoing a coronary bypass operation. Non-invasive serial optical sectioning was carried out by immuno-laser scanning confocal microscopy. Double-labelling for vinculin/alpha-actinin, and the cytoplasmic domain for the beta1 integrin subunit, showed that beta1 integrin is deposited throughout both the vinculin/alpha-actinin domains and the non-vinculin/alpha-actinin domains. These results were supported by a semi-quantitative analysis in extended focus images of the latter preparations. Higher magnification views at the electron microscopical levels of the large, extracellular domain of the beta1 integrin subunit disclosed a pronounced labelling in the form of a dense, irregular punctuate pattern that was distributed at Z-disc domains as well as along the entire sarcolemmal area between Z-discs. Our findings show that in human, myocardial cells, the beta1 integrin receptor does not only localize to the surface membrane at the Z-disc level ('costamere' in cardiac muscle), but has a widespread distribution along the sarcolemma.

Golgi clusters and vesicles mediate mitotic inheritance independently of the endoplasmic reticulum

We have examined the fate of Golgi membranes during mitotic inheritance in animal cells using four-dimensional fluorescence microscopy, serial section reconstruction of electron micrographs, and peroxidase cytochemistry to track the fate of a Golgi enzyme fused to horseradish peroxidase. All three approaches show that partitioning of Golgi membranes is mediated by Golgi clusters that persist throughout mitosis, together with shed vesicles that are often found associated with spindle microtubules. We have been unable to find evidence that Golgi membranes fuse during the later phases of mitosis with the endoplasmic reticulum (ER) as a strategy for Golgi partitioning (Zaal, K.J., C.L. Smith, R.S. Polishchuk, N. Altan, N.B. Cole, J. Ellenberg, K. Hirschberg, J.F. Presley, T.H. Roberts, E. Siggia, et al. 1999. Cell. 99:589-601) and suggest that these results, in part, are the consequence of slow or abortive folding of GFP-Golgi chimeras in the ER. Furthermore, we show that accurate partitioning is accomplished early in mitosis, by a process of cytoplasmic redistribution of Golgi fragments and vesicles yielding a balance of Golgi membranes on either side of the metaphase plate before cell division.

Immunoperoxidase methods for localization of antigens in cultured cells and tissues

This carefully written unit describes two methods for using the immunoperoxidase reaction to localize antigens at the electron microscope level; one for adherent cultured cells and one for tissue sections. The reaction conditions are first optimized at the light microscope level and then adapted for EM level observation. These methods allow for reliable detection of antigens at the cell surface, within the cell, and especially in membrane bounded organelles. Embedding and staining procedures are also optimized for sample visualization.

Chlamydia pneumoniae major outer membrane protein is a surface-exposed antigen that elicits antibodies primarily directed against conformation-dependent determinants

The major outer membrane protein (MOMP) of Chlamydia trachomatis serovariants is known to be an immunodominant surface antigen. Moreover, it is known that the C. trachomatis MOMP elicits antibodies that recognize both linear and conformational antigenic determinants. In contrast, it has been reported that the MOMP of Chlamydia pneumoniae is not surface exposed and is immunorecessive. We hypothesized that the discrepancies between C. trachomatis and C. pneumoniae MOMP exposure on intact chlamydiae and immunogenic properties might be because the focus of the host's immune response is directed to conformational epitopes of the C. pneumoniae MOMP. We therefore conducted studies aimed at defining the surface exposure of MOMP and the conformational dominance of MOMP antibodies. We present here a description of C. pneumoniae species-specific monoclonal antibody (MAb), GZD1E8, which recognizes a conformational epitope on the surface of C. pneumoniae. This MAb is potent in the neutralization of C. pneumoniae infectivity in vitro. Another previously described C. pneumoniae species-specific monoclonal antibody, RR-402, displayed very similar characteristics. However, the antigenic determinant recognized by RR-402 has yet to be identified. We show by immunoprecipitation of C. pneumoniae with GZD1E8 and RR-402 MAbs and by mass spectrometry analysis of immunoprecipitated proteins that both antibodies GZD1E8 and RR-402 recognize the MOMP of C. pneumoniae and that this protein is localized on the surface of the organism. We also show that human sera from C. pneumoniae-positive donors consistently recognize the MOMP by immunoprecipitation, indicating that the MOMP of C. pneumoniae is an immunogenic protein. These findings have potential implications for both C. pneumoniae vaccine and diagnostic assay development.

The mixed lineage kinase DLK is oligomerized by tissue transglutaminase during apoptosis

Current evidence suggests that the mixed lineage kinase family member dual leucine zipper-bearing kinase (DLK) might play a significant role in the regulation of cell growth and differentiation, particularly during the process of tissue remodeling. To further explore this working model, we have investigated the regulation of host and recombinant DLK in NIH3T3 and COS-1 cells undergoing apoptosis. Using calphostin C, a potent and selective inhibitor of protein kinase C and a recognized apoptosis inducer for various cell types, we demonstrate, by immunoblot analysis, that DLK protein levels are rapidly and dramatically down-regulated during the early phases of apoptosis. Down-regulation in calphostin C-treated cells was also accompanied by the appearance of SDS- and mercaptoethanol-resistant high molecular weight DLK immunoreactive oligomers. Experiments aimed at elucidating the mechanism(s) underlying DLK oligomerization revealed that the tissue transglutaminase (tTG) inhibitor monodansylcadaverine antagonized the effects of calphostin C almost completely, thereby suggesting the involvement of a tTG-catalyzed reaction as the root cause of DLK down-regulation and accumulation as high molecular weight species. In support of this notion, we also show that DLK can serve as a substrate for tTG-dependent cross-linking in vitro and that this covalent post-translational modification leads to the functional inactivation of DLK. Taken together, these observations suggest that transglutamination and oligomerization may constitute a relevant physiological mechanism for the regulation of DLK activity.

The p58-positive pre-golgi intermediates consist of distinct subpopulations of particles that show differential binding of COPI and COPII coats and contain vacuolar H(+)-ATPase

We have studied the structural and functional properties of the pre-Golgi intermediate compartment (IC) in normal rat kidney cells using analytical cell fractionation with p58 as the principal marker. The sedimentation profile (sediterm) of p58, obtained by analytical differential centrifugation, revealed in steady-state cells the presence of two main populations of IC elements whose average sedimentation coefficients, s(H)=1150+/-58S (‘heavy’) and s(L)=158+/-8S (‘light’), differed from the s-values obtained for elements of the rough and smooth endoplasmic reticulum. High resolution analysis of these subpopulations in equilibrium density gradients further revealed that the large difference in their s-values was mainly due to particle size. The ‘light’ particle population contained the bulk of COPI and COPII coats, and redistribution of p58 to these particles was observed in transport-arrested cells, showing that the two types of elements are also compositionally distinct and have functional counterparts in intact cells. Using a specific antibody against the 16 kDa proteolipid subunit of the vacuolar H(+)-ATPase, an enrichment of the V(o)domain of the ATPase was observed in the p58-positive IC elements. Interestingly, these elements could contain both COPI and COPII coats and their density distribution was markedly affected by GTP(γ)S. Together with morphological observations, these results demonstrate that, in addition to clusters of small tubules and vesicles, the IC also consists of large-sized structures and corroborate the proposal that the IC elements contain an active vacuolar H(+)-ATPase.

Sorting of membrane and fluid at the apical pole of polarized Madin-Darby canine kidney cells

When fluid-phase markers are internalized from opposite poles of polarized Madin-Darby canine kidney cells, they accumulate in distinct apical and basolateral early endosomes before meeting in late endosomes. Recent evidence suggests that significant mixing of apically and basolaterally internalized membrane proteins occurs in specialized apical endosomal compartments, including the common recycling endosome and the apical recycling endosome (ARE). The relationship between these latter compartments and the fluid-labeled apical early endosome is unknown at present. We report that when the apical recycling marker, membrane-bound immunoglobulin A (a ligand for the polymeric immunoglobulin receptor), and fluid-phase dextran are cointernalized from the apical poles of Madin-Darby canine kidney cells, they enter a shared apical early endosome (</=2.5 min at 37 degrees C) and are then rapidly segregated from one another. The dextran remains in the large supranuclear EEA1-positive early endosomes while recycling polymeric immunoglobulin receptor-bound immunoglobulin A is delivered to a Rab11-positive subapical recycling compartment. This latter step requires an intact microtubule cytoskeleton. Receptor-bound transferrin, a marker of the basolateral recycling pathway, has limited access to the fluid-rich apical early endosome but is excluded from the subapical elements of the Rab11-positive recycling compartment. We propose that the term ARE be used to describe the subapical Rab11-positive compartment and that the ARE is distinct from both the transferrin-rich common recycling endosome and the fluid-rich apical early endosome.

The golgi apparatus is present in perisynaptic, subependymal and perivascular processes of astrocytes and in processes of retinal Müller glia

The Golgi apparatus (GA) of innervated rat and chicken skeletal muscle is present in a typical perinuclear location, and in subsynaptic areas where it disperses after denervation. It was suggested that the subsynaptic segments of the GA are linked with functions involved in the maturation and targeting of synaptic proteins. Similarly, the GA of rat myocardium is found in a perinuclear location and between myofibrils, adjacent to the T system of tubules. These findings raise the question whether the GA of polarized cells is present in a typical perinuclear location, for the performance of general "housekeeping" functions, and in distal areas, for the mediation of specialized functions. Astrocytes may contain GA within their long cytoplasmic processes which are difficult to identify in thin sections. To ensure the astrocytic origin of GA in otherwise unidentifiable small processes, we used transgenic mice expressing the rat MG160 medial Golgi sialoglycoprotein only in the GA of astrocytes, and visualized the GA with monoclonal antibody 10A8 (mAb10A8) which reacts only with rat MG160. Thus, we identified cisternae of the GA in distal perisynaptic and subependymal processes, in perivascular foot plates of cerebral astrocytes, and in processes of the Müller glia in the retina. A similar strategy may be adopted in future investigations aiming at the detection of elements of the GA in distal processes of neurons and oligodendrocytes. The functional implications of GA in perisynaptic astrocytic processes and other processes are unknown. However, the isolation and molecular characterization of the perisynaptic subset of astrocytic Golgi may be feasible, since others have purified the astrocytic glutamate transporter 1 (GLT1) from crude synaptosomal fractions in which astrocytic processes are probably unavoidable contaminants.

The neuronal Golgi apparatus is fragmented in transgenic mice expressing a mutant human SOD1, but not in mice expressing the human NF-H gene

Fragmentation of the Golgi apparatus (GA) of motor neurons was first described in sporadic amyotrophic lateral sclerosis (ALS) and later confirmed in transgenic mice expressing the G93A mutation of the gene encoding the enzyme Cu,Zn superoxide dismutase (SOD1(G93A)) found in some cases of familial ALS. In these transgenic mice, however, the fragmentation of the neuronal GA was associated with cytoplasmic and mitochondrial vacuoles not seen in ALS. The present new series of transgenic mice expressing 14-17 trans gene copies of SOD1(G93A), compared to 25 copies in the mice we studied previously, showed consistent fragmentation of the GA of spinal cord motor neurons, axonal swellings, Lewy-like body inclusions in neurons and glia, but none of the cytoplasmic or mitochondrial vacuoles originally reported. Thus, this animal model recapitulates the clinical and most neuropathological findings of sporadic ALS. Neurofilaments (NF) accumulate in axons and, less often, in neuronal perikarya in most cases of sporadic ALS and they have been implicated in its pathogenesis. In order to investigate whether fragmentation of the neuronal GA also occurs in association with accumulation of perikaryal NFs, we studied the organelle in transgenic mice expressing the heavy subunit of human neurofilaments (NF-H) which developed a motor neuronopathy resembling ALS. The neuronal GA of mice expressing NF-H, however, was intact despite massive accumulation of NFs in both perikarya and axons of motor neurons. In contrast, in transgenic mice expressing SOD1(G93A), the GA was fragmented despite the absence of accumulation of perikaryal NFs. These findings suggest that, in transgenic mice with neuronopathies caused by the expression of mutant SOD1(G93A) or the human NF-H, the GA and the perikaryal NFs are independently involved in the pathogenesis. The evidence suggests that the GA plays a central role in the pathogenesis of the vast majority of sporadic ALS and in FALS with SOD1 mutations.

Phospholipase A(2) antagonists inhibit nocodazole-induced Golgi ministack formation: evidence of an ER intermediate and constitutive cycling

Evidence has been presented both for and against obligate retrograde movement of resident Golgi proteins through the endoplasmic reticulum (ER) during nocodazole-induced Golgi ministack formation. Here, we studied the nocodazole-induced formation of ministacks using phospholipase A(2) (PLA(2)) antagonists, which have been shown previously to inhibit brefeldin A-stimulated Golgi-to-ER retrograde transport. Examination of clone 9 rat hepatocytes by immunofluorescence and immunoelectron microscopy revealed that a subset of PLA(2) antagonists prevented nocodazole-induced ministack formation by inhibiting two different trafficking pathways for resident Golgi enzymes; at 25 microM, retrograde Golgi-to-ER transport was inhibited, whereas at 5 microM, Golgi-to-ER trafficking was permitted, but resident Golgi enzymes accumulated in the ER. Moreover, resident Golgi enzymes gradually redistributed from the juxtanuclear Golgi or Golgi ministacks to the ER in cells treated with these PLA(2) antagonists alone. Not only was ER-to-Golgi transport of resident Golgi enzymes inhibited in cells treated with these PLA(2) antagonists, but transport of the vesicular stomatitis virus G protein out of the ER was also prevented. These results support a model of obligate retrograde recycling of Golgi resident enzymes during nocodazole-induced ministack formation and provide additional evidence that resident Golgi enzymes slowly and constitutively cycle between the Golgi and ER.

Localization of the mixed-lineage kinase DLK/MUK/ZPK to the Golgi apparatus in NIH 3T3 cells

DLK/MUK/ZPK is a serine/threonine kinase that belongs to the mixed-lineage (MLK) subfamily of protein kinases. As is the case for most members of this family, relatively little is known about the physiological role of DLK/MUK/ZPK in mammalian cells. Because analysis of subcellular distribution may provide important clues concerning the potential in vivo function of a protein, an antiserum was generated against the amino terminal region of murine DLK/MUK/ZPK and used for localization studies in wild-type NIH 3T3 cells. Light microscopic immunocytochemistry experiments performed with the antiserum revealed that DLK/MUK/ZPK was specifically localized in a juxtanuclear structure characteristic of the Golgi complex. In support of this, treatment of cells with brefeldin A, a drug known to disintegrate the Golgi apparatus, caused disruption of DLK/MUK/ZPK perinuclear staining. Ultrastructural observation of NIH 3T3 cells also confirmed this localization, showing that most of the immunoreactivity was detected on membranes of the stacked Golgi cisternae. Consistent with localization studies, biochemical analyses revealed that DLK/MUK/ZPK was predominantly associated with Golgi membranes on fractionation of cellular extracts and was entirely partitioned into the aqueous phase when membranes were subjected to Triton X-114 extraction. On the basis of these findings, we suggest that DLK/MUK/ZPK is a peripheral membrane protein tightly associated with the cytoplasmic face of the Golgi apparatus. (J Histochem Cytochem 47:1287-1296, 1999)

The Chlamydia trachomatis IncA protein is required for homotypic vesicle fusion

Chlamydiae replicate within an intracellular vacuole, termed an inclusion, that is non-fusogenic with vesicles of the endosomal or lysosomal compartments. Instead, the inclusion appears to intersect an exocytic pathway from which chlamydiae intercept sphingomyelin en route from the Golgi apparatus to the plasma membrane. Chlamydial protein synthesis is required to establish this interaction. In an effort to identify those chlamydial proteins controlling vesicle fusion, we have prepared polyclonal antibodies against several Chlamydia trachomatis inclusion membrane proteins. Microinjection of polyclonal antibodies against three C. trachomatis inclusion membrane proteins, IncA, F and G, into the cytosol of cells infected with C. trachomatis demonstrates reactivity with antigens on the cytoplasmic face of the inclusion membrane, without apparent inhibition of chlamydial multiplication. Microinjection of antibodies against the C. trachomatis IncA protein, however, results in the development of an aberrant multilobed inclusion structure remarkably similar to that of C. psittaci GPIC. These results suggest that the C. trachomatis IncA protein is involved in homotypic vesicle fusion and/or septation of the inclusion membrane that is believed to accompany bacterial cell division in C. psittaci. This proposal is corroborated by the expression of C. trachomatis and C. psittaci IncA in a yeast two-hybrid system to demonstrate C. trachomatis, but not C. psittaci, IncA interactions. Despite the inhibition of homotypic fusion of C. trachomatis inclusions, fusion of sphingomyelin-containing vesicles with the inclusion was not suppressed.