Detection of Neu1 Sialidase Activity in Regulating TOLL-like Receptor Activation

Mammalian Toll-like receptors (TLRs) are a family of receptors that recognize pathogen-associated molecular patterns. Not only are TLRs crucial sensors of microbial (e.g., viruses, bacteria and parasite) infections, they also play an important role in the pathophysiology of infectious diseases, inflammatory diseases, and possibly in autoimmune diseases. Thus, the intensity and duration of TLR responses against infectious diseases must be tightly controlled. It follows that understanding the structural integrity of sensor receptors, their ligand interactions and signaling components is essential for subsequent immunological protection. It would also provide important opportunities for disease modification through sensor manipulation. Although the signaling pathways of TLR sensors are well characterized, the parameters controlling interactions between the sensors and their ligands still remain poorly defined. We have recently identified a novel mechanism of TLR activation by its natural ligand, which has not been previously observed ^1,2. It suggests that ligand-induced TLR activation is tightly controlled by Neu1 sialidase activation. We have also reported that Neu1 tightly regulates neurotrophin receptors like TrkA and TrkB ³, which involve Neu1 and matrix metalloproteinase-9 (MMP-9) cross-talk in complex with the receptors ⁴. The sialidase assay has been initially use to find a novel ligand, thymoquinone, in the activation of Neu4 sialidase on the cell surface of macrophages, dendritic cells and fibroblast cells via GPCR Gαi proteins and MMP-9 ⁵. For TLR receptors, our data indicate that Neu1 sialidase is already in complex with TLR-2, -3 and -4 receptors, and is induced upon ligand binding to either receptor. Activated Neu1 sialidase hydrolyzes sialyl α-2,3-linked β-galactosyl residues distant from ligand binding to remove steric hinderance to TLR-4 dimerization, MyD88/TLR4 complex recruitment, NFkB activation and pro-inflammatory cell responses. In a collaborative report, Neu1 sialidase has been shown to regulate phagocytosis in macrophage cells ⁶. Taken together, the sialidase assay has provided us with powerful insights to the molecular mechanisms of ligand-induced receptor activation. Although the precise relationship between Neu1 sialidase and the activation of TLR, Trk receptors has yet to be fully elucidated, it would represent a new or pioneering approach to cell regulation pathways.Download video file.^{(57M, mov)}     

Detection of beta-Glucosidase Activity in Polyacrylamide Gels with Esculin as Substrate

beta-Glucosidase can be located after nondenaturing polyacrylamide gel electrophoresis by incubating the gel with 0.1% esculin and 0.03% ferric chloride. The esculetin released from esculin by beta-glucosidase action reacts with ferric ion to produce a black band, corresponding to the beta-glucosidase, against the transparent background.     

Somatostatin: A Novel Substrate and a Modulator of Insulin-Degrading Enzyme Activity

Insulin-degrading enzyme (IDE) is an interesting pharmacological target for Alzheimer's disease (AD), since it hydrolyzes β-amyloid, producing non-neurotoxic fragments. It has also been shown that the somatostatin level reduction is a pathological feature of AD and that it regulates the neprilysin activity toward β-amyloid.In this work, we report for the first time that IDE is able to hydrolyze somatostatin [k_cat (s^− 1) = 0.38 (± 0.05); K_m (M) = 7.5 (± 0.9) × 10^− 6] at the Phe6-Phe7 amino acid bond. On the other hand, somatostatin modulates IDE activity, enhancing the enzymatic cleavage of a novel fluorogenic β-amyloid through a decrease of the K_m toward this substrate, which corresponds to the 10-25 amino acid sequence of the Aβ(1-40). Circular dichroism spectroscopy and surface plasmon resonance imaging experiments show that somatostatin binding to IDE brings about a concentration-dependent structural change of the secondary and tertiary structure(s) of the enzyme, revealing two possible binding sites. The higher affinity binding site disappears upon inactivation of IDE by ethylenediaminetetraacetic acid, which chelates the catalytic Zn²⁺ ion. As a whole, these features suggest that the modulatory effect is due to an allosteric mechanism: somatostatin binding to the active site of one IDE subunit (where somatostatin is cleaved) induces an enhancement of IDE proteolytic activity toward fluorogenic β-amyloid by another subunit. Therefore, this investigation on IDE-somatostatin interaction contributes to a more exhaustive knowledge about the functional and structural aspects of IDE and its pathophysiological implications in the amyloid deposition and somatostatin homeostasis in the brain.     

Block Staining of Mammalian Tissues with Hematoxylin and Eosin

Various mammalian tissues were stained en bloc with hematoxylin and eosin after fixation and prior to embedding in paraffin wax and sectioning. The choice of fixative is important and best results are obtained using Worcester's Fluid, a combination of saturated aqueous mercuric chloride, formaldehyde, and glacial acetic acid. After fixation, blocks of tissue up to 1.5 cm thick are stained for seven days in hematoxylin. Excess stain is removed by washing tissues in running water overnight. Tissue blocks then are dehydrated with graded concentrations of ethyl alcohols to 80% and counterstained, with further dehydration, in 0.5% spirit soluble eosin in 90% ethyl alcohol for five days. The tissue is subsequently transferred to 90% ethyl alcohol overnight to differentiate eosin staining; dehydration is completed in absolute ethyl alcohol. The blocks are cleared in cedarwood oil and briefly in xylene prior to embedding, sectioning, and mounting. Following removal of wax by xylene, coverslips are applied.

General morphological and histological features were particularly well differentiated and very selectively and reliably stained by this method.     

Sialidase Activity in Nuclear Membranes of Rat Brain

Abstract: A highly purified nuclear membrane preparation was obtained from adult rat brain and examined for sialidase activity using GM3, GD1a, GD1b, or N -acetylneuramin lactitol as the substrate. The nuclear membranes contained an appreciable level of sialidase activity; the specific activities toward GM3 and N -acetylneuramin lactitol were 20.5 and 23.8% of the activities in the total brain homogenate, respectively. The sialidase activity in nuclear membranes showed substrate specificity distinct from other membrane-bound sialidases localized in lysosomal membranes, synaptosomal plasma membranes, or myelin membranes. These results strongly suggest the existence of a sialidase activity associated with the nuclear membranes from rat brain.     

宫颈癌组织人乳头瘤病毒的荧光偏振基因分型

采用荧光偏振人乳头瘤病毒(human papillomavirus,HPV)分型新方法探讨了8种常见型别HPV在陕西宫颈癌患者中的流行情况。首先,用HPV GP5 ／GP6 通用引物PCR扩增65例早期宫颈癌(Ⅱa期内)和72例慢性宫颈炎病变组织DNA粗提物,继之将模板指导的末端延伸反应与荧光偏振检测技术结合(TDI-FP),用GP5 ／GP6 扩增区内的HPV6、11、16、18、31、33、35和58型特异性探针与PCR产物杂交后,荧光素标记的特异碱基(TAMRA-ddTTP或R110-ddGTP)在GP5 ／GP6 产物中相应的模板指导下,掺入延伸至相应探针末端,致使对应的TAMRA或R110 FP值升高,从而对扩增的HPV阳性产物进行HPV分型。65例宫颈癌患者中检出HPV57例,阳性率87．69％,72例慢性宫颈炎患者中检出HPV28例,阳性率38．89％,两组间HPV阳性率有显著性差异。宫颈癌与慢性宫颈炎患者中4种最常见的HPV型别分别是HPV 16(45．6％)、HPV 18(22．8％)、HPV 58(17．5％)、HPV 31(7．02％)和HPV 16(35．7％)、HPV 11(32．1％)、HPV 6(21．4％)、HPV 18(10．7％)。慢性宫颈炎患者中检出的HPV型别57．14％属高危型。HPV 16在两组中均最为多见。中国陕西宫颈疾病患者中HPV感染有其特点,世界范围内少见的HPV 58在陕西宫颈癌与慢性宫颈炎患者中均较为多见,在进行HPV新诊断方法及疫苗研制时应考虑到这种特点。     

A Novel Fluorescent Sensor Protein for Visualization of Redox States in the Cytoplasm and in Peroxisomes

Reactive oxygen species are generated within peroxisomes during peroxisomal metabolism. However, due to technological difficulties, the intraperoxisomal redox state remain elusive, and the effect of peroxisome deficiency on the intracellular redox state is controversial. A newly developed, genetically encoded fluorescence resonance energy transfer (FRET) probe, Redoxfluor, senses the physiological redox state via its internal disulfide bonds, resulting in a change in the conformation of the protein leading to a FRET response. We made use of Redoxfluor to measure the redox states at the subcellular level in yeast and Chinese hamster ovary (CHO) cells. In wild-type peroxisomes harboring an intact fatty acid β-oxidation system, the redox state within the peroxisomes was more reductive than that in the cytosol, despite the fact that reactive oxygen species were generated within the peroxisomes. Interestingly, we observed that the redox state of the cytosol of cell mutants for peroxisome assembly, regarded as models for a neurological metabolic disorder, was more reductive than that of the wild-type cells in yeast and CHO cells. Furthermore, Redoxfluor was utilized to develop an efficient system for the screening of drugs that moderate the abnormal cytosolic redox state in the mutant CHO cell lines for peroxisome assembly without affecting the redox state of normal cells.Peroxisomes are single membrane-bound organelles harboring at least one H₂O₂-generating oxidase and one H₂O₂-decomposing catalase, and they are present in virtually all eukaryotic cells, from yeast to mammals. The most conserved activity of peroxisomal metabolism is the β-oxidation of fatty acids (27).Peroxisome assembly requires more than 20 PEX gene products, termed peroxins, in any given organism (5). The impairment of peroxisomal protein transport caused by mutations in PEX genes causes fatal human peroxisome biogenesis disorders (PBDs) (34). In the cells of such PBD patients, essential enzymes normally localized to peroxisomes are found mostly in the cytosol. Mammalian cell lines harboring mutations in peroxins (including fibroblasts from PBD patients) grow well in cell culture. On the other hand, pex mutants of the methylotrophic yeast Pichia pastoris can grow normally on glucose but not oleate or methanol (37).Peroxisomal metabolic pathways can generate a high level of reactive oxygen species (ROS) (32). Therefore, peroxisomal disorders have been studied with a focus on the generation of ROS. However, the relationship between PBDs and the intracellular redox state is unclear (13, 32).Peroxisomes have long been thought to be in a more highly oxidized state than the cytosol due to this generation of ROS. However, there is no reported experimental evidence supporting this notion. We previously identified a 20-kDa peroxisomal membrane protein, named Pmp20, in methanol-induced peroxisomes of methylotrophic yeasts. Pmp20 had a glutathione (GSH) peroxidase activity, suggesting the presence of glutathione within the peroxisomes (9). However, we and other groups of investigators have been unable to determine the levels of the reduced and oxidized forms of glutathione due to technical difficulties and therefore have been unable to assess the redox state within peroxisomes by conventional biochemical methods.In general, the intracellular redox state is determined by the levels of redox-related metabolites that are generated by multiple metabolic pathways. (We herein refer to the “redox state” as an intracellular environment at steady state, which is distinct from oxidative stress or ROS, which functions as a signal for further intracellular events such as apoptosis.) Therefore, the redox state is considered to reflect the overall metabolic status. While the standard redox potential (E₀′) is a general index used to express the redox state of a compound, it cannot be used to describe the intracellular redox state because it does not take into account various physiological considerations, such as the cytosol, where many compounds coexist in a mixture of various redox states (14). Therefore, the equilibrium redox state in living cells has been estimated from indices such as the ratio of oxidized and reduced forms of glutathione, from indirect indices of the redox state, such as the NAD(P)H ratio (12, 40), or from the level of the expression of antioxidant enzymes. However, the measurement of these indices often yields contradictory results, making it difficult to evaluate the physiological redox state using any single index. This situation might have led to misunderstanding the redox state in cells from patients with PBDs. Reductive conditions could occur during conditions of oxidative stress, when the ROS defense system is functioning normally.With the aim of determining the intracellular redox state directly, we developed a fluorescent redox probe, Redoxfluor, with a novel sensing mechanism. Several green fluorescent protein (GFP) variants that report the in vivo redox state (roGFP [4, 7], rxYFP [18, 24, 25]) or H₂O₂ level (HyPer [3]) have been developed since the start of our research. However, none of these reporters have been used to visualize the redox state in mammalian cytosol, and differences in the redox potential between normal and pathological states have not been reported.In the present work, we developed a Redoxfluor that discriminates the redox state of peroxisome assembly mutant cell lines (34) from that of the normal cell line. Our findings shed light on how to tackle problems with monitoring the spatiotemporal dynamics of the redox state within living mammalian cells and also should pave the way for the development of a screen for drugs that can affect various metabolic disorders with abnormal redox state.     

Biochemical Insight into Novel Rab-GEF Activity of the Mammalian TRAPPIII Complex

Transport Protein Particle complexes (TRAPP) are evolutionarily conserved regulators of membrane trafficking, with this mediated by their guanine nucleotide exchange factor (GEF) activity towards Rab GTPases. In metazoans evidence suggests that two different TRAPP complexes exist, TRAPPII and TRAPPIII. These two complexes share a common core of subunits, with complex specific subunits (TRAPPC9 and TRAPPC10 in TRAPPII and TRAPPC8, TRAPPC11, TRAPPC12, TRAPPC13 in TRAPPIII). TRAPPII and TRAPPIII have distinct specificity for GEF activity towards Rabs, with TRAPPIII acting on Rab1, and TRAPPII acting on Rab1 and Rab11. The molecular basis for how these complex specific subunits alter GEF activity towards Rab GTPases is unknown. Here we have used a combination of biochemical assays, hydrogen deuterium exchange mass spectrometry (HDX-MS) and electron microscopy to examine the regulation of TRAPPII and TRAPPIIII complexes in solution and on membranes. GEF assays revealed that TRAPPIII has GEF activity against Rab1 and Rab43, with no detectable activity against the other 18 Rabs tested. The TRAPPIII complex had significant differences in protein dynamics at the Rab binding site compared to TRAPPII, potentially indicating an important role of accessory subunits in altering the active site of TRAPP complexes. Both the TRAPPII and TRAPPIII complexes had enhanced GEF activity on lipid membranes, with HDX-MS revealing numerous conformational changes that accompany membrane association. HDX-MS also identified a membrane binding site in TRAPPC8. Collectively, our results provide insight into the functions of TRAPP complexes and how they can achieve Rab specificity.     

Detection of the Genome and Transcripts of a Persistent DNA Virus in Neuronal Tissues by Fluorescent In situ Hybridization Combined with Immunostaining

Single cell codetection of a gene, its RNA product and cellular regulatory proteins is critical to study gene expression regulation. This is a challenge in the field of virology; in particular for nuclear-replicating persistent DNA viruses that involve animal models for their study. Herpes simplex virus type 1 (HSV-1) establishes a life-long latent infection in peripheral neurons. Latent virus serves as reservoir, from which it reactivates and induces a new herpetic episode. The cell biology of HSV-1 latency remains poorly understood, in part due to the lack of methods to detect HSV-1 genomes in situ in animal models. We describe a DNA-fluorescent in situ hybridization (FISH) approach efficiently detecting low-copy viral genomes within sections of neuronal tissues from infected animal models. The method relies on heat-based antigen unmasking, and directly labeled home-made DNA probes, or commercially available probes. We developed a triple staining approach, combining DNA-FISH with RNA-FISH and immunofluorescence, using peroxidase based signal amplification to accommodate each staining requirement. A major improvement is the ability to obtain, within 10 µm tissue sections, low-background signals that can be imaged at high resolution by confocal microscopy and wide-field conventional epifluorescence. Additionally, the triple staining worked with a wide range of antibodies directed against cellular and viral proteins. The complete protocol takes 2.5 days to accommodate antibody and probe penetration within the tissue.     

Density-Dependent Changes in Gangliosides and Sialidase Activity of Murine Neuroblastoma Cells

Abstract: Density-dependent changes in ganglioside composition, Vibrio cholerae neuraminidase (VCN)-susceptible sialyl residues, and membrane- associated sialidase activity were determined for the cholinergic murine neuroblastoma cell line S20Y. A decrease in total ganglioside sialic acid and VCN-releasable sialic acid was observed with increasing cell density. G^M3 was the major ganglioside component of preconfluent S20Y cells, whereas G_DIA was predominant in postconfluent cells. Sialidase activity increased in confluent and postconfluent cells and may account for the reduction in total ganglioside sialic acid observed with increasing cell density. In contrast, while adrenergic N115 cells showed a decrease in VCN-susceptible sialic acid residues with increasing cell density, there was no significant change in ganglioside composition or ganglioside sialic acid levels.     

Easy and Rapid Detection of Mumps Virus by Live Fluorescent Visualization of Virus-Infected Cells

Mumps viruses show diverse cytopathic effects (CPEs) of infected cells and viral plaque formation (no CPE or no plaque formation in some cases) depending on the viral strain, highlighting the difficulty in mumps laboratory studies. In our previous study, a new sialidase substrate, 2-(benzothiazol-2-yl)-4-bromophenyl 5-acetamido-3,5-dideoxy-α-D-glycero-D-galacto-2-nonulopyranosidonic acid (BTP3-Neu5Ac), was developed for visualization of sialidase activity. BTP3-Neu5Ac can easily and rapidly perform histochemical fluorescent visualization of influenza viruses and virus-infected cells without an antiviral antibody and cell fixation. In the present study, the potential utility of BTP3-Neu5Ac for rapid detection of mumps virus was demonstrated. BTP3-Neu5Ac could visualize dot-blotted mumps virus, virus-infected cells, and plaques (plaques should be called focuses due to staining of infected cells in this study), even if a CPE was not observed. Furthermore, virus cultivation was possible by direct pick-up from a fluorescent focus. In conventional methods, visible appearance of the CPE and focuses often requires more than 6 days after infection, but the new method with BTP3-Neu5Ac clearly visualized infected cells after 2 days and focuses after 4 days. The BTP3-Neu5Ac assay is a precise, easy, and rapid assay for confirmation and titration of mumps virus.     

Visualization of Active Glucocerebrosidase in Rodent Brain with High Spatial Resolution following In Situ Labeling with Fluorescent Activity Based Probes

Gaucher disease is characterized by lysosomal accumulation of glucosylceramide due to deficient activity of lysosomal glucocerebrosidase (GBA). In cells, glucosylceramide is also degraded outside lysosomes by the enzyme glucosylceramidase 2 (GBA2) of which inherited deficiency is associated with ataxias. The interest in GBA and glucosylceramide metabolism in the brain has grown following the notion that mutations in the GBA gene impose a risk factor for motor disorders such as α-synucleinopathies. We earlier developed a β-glucopyranosyl-configured cyclophellitol-epoxide type activity based probe (ABP) allowing in vivo and in vitro visualization of active molecules of GBA with high spatial resolution. Labeling occurs through covalent linkage of the ABP to the catalytic nucleophile residue in the enzyme pocket. Here, we describe a method to visualize active GBA molecules in rat brain slices using in vivo labeling. Brain areas related to motor control, like the basal ganglia and motor related structures in the brainstem, show a high content of active GBA. We also developed a β-glucopyranosyl cyclophellitol-aziridine ABP allowing in situ labeling of GBA2. Labeled GBA2 in brain areas can be identified and quantified upon gel electrophoresis. The distribution of active GBA2 markedly differs from that of GBA, being highest in the cerebellar cortex. The histological findings with ABP labeling were confirmed by biochemical analysis of isolated brain areas. In conclusion, ABPs offer sensitive tools to visualize active GBA and to study the distribution of GBA2 in the brain and thus may find application to establish the role of these enzymes in neurodegenerative disease conditions such as α-synucleinopathies and cerebellar ataxia.     

Quantitative Visualization and Detection of Skin Cancer Using Dynamic Thermal Imaging

In 2010 approximately 68,720 melanomas will be diagnosed in the US alone, with around 8,650 resulting in death ¹. To date, the only effective treatment for melanoma remains surgical excision, therefore, the key to extended survival is early detection ^2,3. Considering the large numbers of patients diagnosed every year and the limitations in accessing specialized care quickly, the development of objective in vivo diagnostic instruments to aid the diagnosis is essential. New techniques to detect skin cancer, especially non-invasive diagnostic tools, are being explored in numerous laboratories. Along with the surgical methods, techniques such as digital photography, dermoscopy, multispectral imaging systems (MelaFind), laser-based systems (confocal scanning laser microscopy, laser doppler perfusion imaging, optical coherence tomography), ultrasound, magnetic resonance imaging, are being tested. Each technique offers unique advantages and disadvantages, many of which pose a compromise between effectiveness and accuracy versus ease of use and cost considerations. Details about these techniques and comparisons are available in the literature ⁴.Infrared (IR) imaging was shown to be a useful method to diagnose the signs of certain diseases by measuring the local skin temperature. There is a large body of evidence showing that disease or deviation from normal functioning are accompanied by changes of the temperature of the body, which again affect the temperature of the skin ^5,6. Accurate data about the temperature of the human body and skin can provide a wealth of information on the processes responsible for heat generation and thermoregulation, in particular the deviation from normal conditions, often caused by disease. However, IR imaging has not been widely recognized in medicine due to the premature use of the technology ^7,8 several decades ago, when temperature measurement accuracy and the spatial resolution were inadequate and sophisticated image processing tools were unavailable. This situation changed dramatically in the late 1990s-2000s. Advances in IR instrumentation, implementation of digital image processing algorithms and dynamic IR imaging, which enables scientists to analyze not only the spatial, but also the temporal thermal behavior of the skin ⁹, allowed breakthroughs in the field.In our research, we explore the feasibility of IR imaging, combined with theoretical and experimental studies, as a cost effective, non-invasive, in vivo optical measurement technique for tumor detection, with emphasis on the screening and early detection of melanoma ^10-13. In this study, we show data obtained in a patient study in which patients that possess a pigmented lesion with a clinical indication for biopsy are selected for imaging. We compared the difference in thermal responses between healthy and malignant tissue and compared our data with biopsy results. We concluded that the increased metabolic activity of the melanoma lesion can be detected by dynamic infrared imaging.     

应用实时荧光定量RT-PCR检测宫颈癌及其外周血中VEGF表达的研究

目的:研究血管内皮生长因子在宫颈癌患者癌和癌旁组织及外周血循环细胞中的表达情况,分析其在肿瘤生长与转移中的作用。方法:采用基于TaqMan探针技术的实时荧光定量RT-PCR法检测了50例宫颈癌患者癌及癌旁组织和40例正常宫颈组织标本中VEGF mRNA的表达情况及其对应的外周血中的VEGF mRNA表达,分析其与临床病理参数之间的关系。结果:宫颈癌组织及癌旁组织中VEGF mRNA的表达水平无明显差异,但均与正常宫颈组织的表达水平差异有显著性;宫颈癌组织中VEGF mRNA的表达与肿瘤的组织学类型无明显的相关性;而与肿瘤的临床病理分期、病理分化程度、淋巴结转移、肿瘤直径、深肌层浸润间均呈显著的正相关。宫颈癌患者外周血中VEGF的表达明显高于对照组水平,与淋巴结是否转移密切相关,但与其他临床病理参数无关。结论:实时荧光定量RT-PCR可以敏感且特异性的检测出宫颈癌组织及外周血中VEGF mRNA的表达,且方法准确可靠,操作方便,在肿瘤的微转移的诊断监测方面有一定的应用价值。VEGF有可能成为治疗恶性肿瘤的一个潜在的分子靶点。     

Structure and Activity of Human Mitochondrial Peptide Deformylase, a Novel Cancer Target

Peptide deformylase proteins (PDFs) participate in the N-terminal methionine excision pathway of newly synthesized peptides. We show that the human PDF (HsPDF) can deformylate its putative substrates derived from mitochondrial DNA-encoded proteins. The first structural model of a mammalian PDF (1.7 Å), HsPDF, shows a dimer with conserved topology of the catalytic residues and fold as non-mammalian PDFs. The HsPDF C-terminus topology and the presence of a helical loop (H2 and H3), however, shape a characteristic active site entrance. The structure of HsPDF bound to the peptidomimetic inhibitor actinonin (1.7 Å) identified the substrate-binding site. A defined S1′ pocket, but no S2′ or S3′ substrate-binding pockets, exists. A conservation of PDF-actinonin interaction across PDFs was observed. Despite the lack of true S2′ and S3′ binding pockets, confirmed through peptide binding modeling, enzyme kinetics suggest a combined contribution from P2′and P3′ positions of a formylated peptide substrate to turnover.     

Imaging the Dynamics of Endocytosis in Live Mammalian Tissues

In mammalian cells, endocytosis plays a pivotal role in regulating several basic cellular functions. Up to now, the dynamics and the organization of the endocytic pathways have been primarily investigated in reductionist model systems such as cell and organ cultures. Although these experimental models have been fully successful in unraveling the endocytic machinery at a molecular level, our understanding of the regulation and the role of endocytosis in vivo has been limited. Recently, advancements in intravital microscopy have made it possible to extend imaging in live animals to subcellular structures, thus revealing new aspects of the molecular machineries regulating membrane trafficking that were not previously appreciated in vitro. Here, we focus on the use of intravital microscopy to study endocytosis in vivo, and discuss how this approach will allow addressing two fundamental questions: (1) how endocytic processes are organized in mammalian tissues, and (2) how they contribute to organ physiopathology.Endocytosis is a fundamental process used by the cell to internalize molecules from the plasma membrane (Mellman 1996; Doherty and McMahon 2009), and its dysregulation is the cause of several pathological conditions, such as cancer and neurodegenerative, metabolic, and storage diseases (Lanzetti and Di Fiore 2008; Mosesson et al. 2008; Ballabio and Gieselmann 2009).In mammals, endocytosis has been primarily studied in cell culture, which has been instrumental in identifying various endocytic pathways and elucidating the trafficking of internalized molecules throughout the endolysosomal system (Conner and Schmid 2003; Maxfield and McGraw 2004; Donaldson et al. 2009; Hurley and Stenmark 2011). The degree of complexity in the organization and the regulation of the endocytic processes have been shown to substantially increase in polarized cells (Mostov et al. 2003; Folsch et al. 2009) and in organ cultures (Dunn et al. 1980; Kandimalla et al. 2009; Khandelwal et al. 2010), which recapitulate some of the architectural features of the intact tissue. The scenario is further complicated in live animals, where tissues are continuously exposed to a specific combination of cues coming from the vasculature, the central nervous system, and the extracellular environment, which are difficult to reconstitute accurately in vitro. Therefore, although our knowledge of the molecular machineries controlling mammalian endocytosis has substantially increased in the last decades, there are still fundamental issues that have not been explored yet, such as how endocytic pathways are organized and regulated in mammalian tissues. Specifically, it is fundamental to establish whether in vivo cells show the same regulation of endocytic pathways that has been reported in vitro, or how molecules are internalized and trafficked in the presence of physiological levels of ligands and regulatory molecules. Another question is what is the contribution of the endocytic pathways to the physiopathology of a specific tissue or organ. For example, it is of paramount importance to determine whether and how endocytic pathways are altered in epithelial and stromal cells during tumor development and progression, and which specific cell function is affected by their dysregulation.Investigations of endocytosis in live mammals (i.e., rodents) were extensively performed during the 1980s and 1990s by using conventional techniques (e.g., biochemical assays, EM, and indirect immunofluorescence). However, the advent of the green fluorescent protein (GFP) technology, which has enabled imaging subcellular organelles in real time, has significantly shifted the focus toward cell cultures.The recent advancements in intravital microscopy (IVM), which encompasses a series of light microscopy–based techniques, have now made possible imaging biological processes in live animals at a subcellular resolution (Weigert et al. 2013). In this perspective, we focus on reviewing most of the recent data on IVM and endocytosis and try to convey to the reader a sense of the potential, challenges, and limitations of this approach. However, before discussing the “heart of the matter,” we start by briefly pointing out the advantages of using animal models versus the more popular and well-established in vitro model systems.     

Use of the Protease Fluorescent Detection Kit to Determine Protease Activity

The Protease Fluorescent Detection Kit provides ready-to-use reagents for detecting the presence of protease activity. This simple assay to detect protease activity uses casein labeled with fluorescein isothiocyanate (FITC) as the substrate.Protease activity results in the cleavage of the FITC-labeled casein substrate into smaller fragments, which do not precipitate under acidic conditions. After incubation of the protease sample and substrate, the reaction is acidified with the addition of trichloroacetic acid (TCA). The mixture is then centrifuged with the undigested substrate forming a pellet and the smaller, acid soluble fragments remaining in solution. The supernatant is neutralized and the fluorescence of the FITC-labeled fragments is measured.The described kit procedure detects the trypsin protease control at a concentration of approximately 0.5 μg/ml (5 ng of trypsin added to the assay). This sensitivity can be increased with a longer incubation time, up to 24 hours. The assay is performed in microcentrifuge tubes and procedures are provided for fluorescence detection using either cuvettes or multiwell plates.Download video file.^{(52M, flv)}     

Detection of β-Glucosidase Activity in Polyacrylamide Gels with Esculin as Substrate

β-Glucosidase can be located after nondenaturing polyacrylamide gel electrophoresis by incubating the gel with 0.1% esculin and 0.03% ferric chloride. The esculetin released from esculin by β-glucosidase action reacts with ferric ion to produce a black band, corresponding to the β-glucosidase, against the transparent background.     

人尿嘧啶糖基化酶cDNA的克隆及其在食管鳞癌组织中的检测

尿嘧啶糖基化酶是碱基切除修复过程的起始酶,对于维护基因稳定具有重要意义。在不同组织及不同细胞周期中,该酶的表达水平存在差异。通过反转录PCR克隆了人尿嘧啶糖基化酶的cDNA编码序列,进一步以克隆所得的已知UNG基因拷贝数的重组质粒作为定量标准,通过实时荧光定量RT-PCR测定了食管癌病人手术切除组织中尿嘧啶糖基化酶的mRNA水平,探讨了尿嘧啶糖基化酶表达水平与食管癌之间的联系。