Direct observation of Staphylococcus aureus cell wall digestion by lysostaphin

The advent of Staphylococcus aureus strains that are resistant to virtually all antibiotics has increased the need for new antistaphylococcal agents. An example of such a potential therapeutic is lysostaphin, an enzyme that specifically cleaves the S. aureus peptidoglycan, thereby lysing the bacteria. Here we tracked over time the structural and physical dynamics of single S. aureus cells exposed to lysostaphin, using atomic force microscopy. Topographic images of native cells revealed a smooth surface morphology decorated with concentric rings attributed to newly formed peptidoglycan. Time-lapse images collected following addition of lysostaphin revealed major structural changes in the form of cell swelling, splitting of the septum, and creation of nanoscale perforations. Notably, treatment of the cells with lysostaphin was also found to decrease the bacterial spring constant and the cell wall stiffness, demonstrating that structural changes were correlated with major differences in cell wall nanomechanical properties. We interpret these modifications as resulting from the digestion of peptidoglycan by lysostaphin, eventually leading to the formation of osmotically fragile cells. This study provides new insight into the lytic activity of lysostaphin and offers promising prospects for the study of new antistaphylococcal agents.     

Immunization with a lentivector that targets tumor antigen expression to dendritic cells induces potent CD8+ and CD4+ T-cell responses

Lentivectors stimulate potent immune responses to antigen transgenes and are being developed as novel genetic vaccines. To improve safety while retaining efficacy, we constructed a lentivector in which transgene expression was restricted to antigen-presenting cells using the mouse dectin-2 gene promoter. This lentivector expressed a green fluorescent protein (GFP) transgene in mouse bone marrow-derived dendritic cell cultures and in human skin-derived Langerhans and dermal dendritic cells. In mice GFP expression was detected in splenic dectin-2⁺ cells after intravenous injection and in CD11c⁺ dendritic cells in the draining lymph node after subcutaneous injection. A dectin-2 lentivector encoding the human melanoma antigen NY-ESO-1 primed an NY-ESO-1-specific CD8⁺ T-cell response in HLA-A2 transgenic mice and stimulated a CD4⁺ T-cell response to a newly identified NY-ESO-1 epitope presented by H2 I-A^b. As immunization with the optimal dose of the dectin-2 lentivector was similar to that stimulated by a lentivector containing a strong constitutive viral promoter, targeting antigen expression to dendritic cells can provide a safe and effective vaccine.     

αII-Spectrin Regulates Invadosome Stability and Extracellular Matrix Degradation

Invadosomes are actin-rich adhesion structures involved in tissue invasion and extracellular matrix (ECM) remodelling. αII-Spectrin, an ubiquitous scaffolding component of the membrane skeleton and a partner of actin regulators (ABI1, VASP and WASL), accumulates highly and specifically in the invadosomes of multiple cell types, such as mouse embryonic fibroblasts (MEFs) expressing SrcY527F, the constitutively active form of Src or activated HMEC-1 endothelial cells. FRAP and live-imaging analysis revealed that αII-spectrin is a highly dynamic component of invadosomes as actin present in the structures core. Knockdown of αII-spectrin expression destabilizes invadosomes and reduces the ability of the remaining invadosomes to digest the ECM and to promote invasion. The ECM degradation defect observed in spectrin-depleted-cells is associated with highly dynamic and unstable invadosome rings. Moreover, FRAP measurement showed the specific involvement of αII-spectrin in the regulation of the mobile/immobile β3-integrin ratio in invadosomes. Our findings suggest that spectrin could regulate invadosome function and maturation by modulating integrin mobility in the membrane, allowing the normal processes of adhesion, invasion and matrix degradation. Altogether, these data highlight a new function for spectrins in the stability of invadosomes and the coupling between actin regulation and ECM degradation.     

Dynamic Contrast Enhanced Magnetic Resonance Imaging of an Orthotopic Pancreatic Cancer Mouse Model

Dynamic contrast enhanced magnetic resonance imaging (DCE-MRI) has been limitedly used for orthotopic pancreatic tumor xenografts due to severe respiratory motion artifact in the abdominal area. Orthotopic tumor models offer advantages over subcutaneous ones, because those can reflect the primary tumor microenvironment affecting blood supply, neovascularization, and tumor cell invasion. We have recently established a protocol of DCE-MRI of orthotopic pancreatic tumor xenografts in mouse models by securing tumors with an orthogonally bent plastic board to prevent motion transfer from the chest region during imaging. The pressure by this board was localized on the abdominal area, and has not resulted in respiratory difficulty of the animals. This article demonstrates the detailed procedure of orthotopic pancreatic tumor modeling using small animals and DCE-MRI of the tumor xenografts. Quantification method of pharmacokinetic parameters in DCE-MRI is also introduced. The procedure described in this article will assist investigators to apply DCE-MRI for orthotopic gastrointestinal cancer mouse models.     

Die afferente Hörbahn im Bereich des Zentralnervensystems vonDecticus verrucivorus (Tettigoniidae)

Zusammenfassung Die Hörbahn vonDecticus verrucivorus (Tettigoniidae) wird im Bereich des Zentralnervensystems elektrophysiologisch untersucht. Zur akustischen Reizung dienen Kunstlaute (Weißes Rauschen und reine Sinustöne variabler Frequenz, Intensität, Dauer, Richtung und Wiederholungsrate) und Stridulationsgesänge der eigenen Art sowie von 11 weiteren im gleichen Biotop vorkommenden Orthopterenarten.Auf jeder Seite des Bauchmarks konnten 19 Sekundärneuronentypen gefunden und klassifiziert werden. Davon haben 8 Neuronentypen T-Struktur, 5 Typen sind aufsteigende und 6 Typen sind absteigende Sekundärneuronen. Aus dem Supraösophagealganglion werden 8 Typen von Tertiärneuronen beschrieben. Die Gesamtstruktur wird in Abb. 1 dargestellt. Da einige Neuronentypen durch 2 Neuronen auf jeder Seite repräsentiert werden, und mehrere Neuronen nicht klassifiziert werden konnten, handelt es sich sicher noch um ein Minimalsystem.Die von 33 tympanalen Fasern (Primärneuronen) kommende Information wird im Synapsenbereich des Prothorakalganglions umgeschaltet und durch eine etwa gleichgroße Anzahl von Sekundärneuronen weitergeleitet. Die Schallparameter bestimmter Bereiche werden betont. Zwischen 3 kHz und 40 kHz ist eine Frequenzanalyse möglich; die dominanten Anteile arteigener Stridulationslaute ( 14 kHz) werden bevorzugt beantwortet. Eine genaue Intensitäts- und Richtungsbestimmung wird vom auditiven System im Bereich von 25–100 dB durchgeführt. Die Codierung dieser Infomation wird durch proportionale Intensitätsbeantwortung, durch Betonung verschiedener Intensitätsbereiche und durch Vergleich abgestufter Schwellen erreicht. Die genaue Messung der Reizdauer und der Reizrate wird durch unterschiedliche Habituation tonisch reagierender Neuronen ermöglicht.Die arteigenen Laute rufen maximale Antworten hervor. Die Unterscheidung der einzelnen Schallparameter und der Stridulationsgesänge wird auf dem Niveau der hier beschriebenen Tertiärneuronen nicht wesentlich verbessert.

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The afferent auditory system in the CNS ofDecticus verrucivorus (Tettigoniidae)

Summary The central auditory system ofDecticus verrucivorus (Tettigoniidae) was investigated electrophysiologically. Artificial sounds and stridulation songs of the species itself and also of eleven other species living in the same biotope were used for acoustic stimulation. The artificial sounds were white noise and pure sinusoidal sounds of variable frequencies, intensities, durations, directions, and repetition rates.Nineteen types of second-order neurons were found and classified on each side of the ventral nerve cord. Eight types of these neurons are T shaped, five are ascending ones, and six are descending neurons. Eight types of third-order neurons were found in the supraesophageal ganglion.The structure of the auditory system described here is shown in Fig. 1. It still must be considered as a minimal system as some types are represented by two neurons on each side and several neurons could not be classified.The acoustic information from the 33 tympanic axons (first-order neurons) is transmitted synaptically in the prothoracic ganglion and is conducted by approximately the same number of second-order neurons. The parameters of certain ranges in the sound field are accentuated. The pitch discrimination allows the measurement of frequencies from 3–40 kHz. The dominant frequencies in the stridulation song ofDecticus verrucivorus ( 14 kHz) are preferentially answered. Intensities and sound directions are measured in detail to within 25–100 dB by the nervous system. Proportional coding of the intensity is achieved by accentuation of certain ranges of intensity, and be comparison of different thresholds. The different habituating neurons which show a tonic reaction measure the duration and the repetition rate.When the auditory system is stimulated with natural sounds the species-specific songs cause maximal reactions. The third-order neurons here described do not analyze the different sounds better than the second-order neurons.

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Im Rahmen des Sonderforschungsbereiches 114 (Bionach) Bochum; gefördert durch die Deutsche Forschungsgemeinschaft.

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Herrn Prof. Dr. J. Schwartzkopff danken wir für die kritische Durchsicht des Manuskriptes, Herrn Prof. Dr. F. Huber für anregende Diskussionen, Herrn Dr.-Ing. G. J. Dörrscheidt für die Entwicklung eines Computerprogramms, Herrn Dr. P. A. Us (Ljubljana) für die Bestimmung einiger Orthopterenarten und Frau Ch. Klotz, Frl. M. Düpjohann, Frl. B. Wasserka für die technische Hilfe.     

Characteristics of amino acid accumulation by isolated intestinal epithelial cells

Summary Accumulation of neutral amino acids by isolated chick epithelial cells has been studied and the results discussed in terms of the ion gradient model, and a model invoking a direct input of metabolic energy. The cells establish four- to eightfold concentration gradients of amino acids at an extracellular concentration of 1mm. The accumulation is sodium-dependent, inhibited by high extracellular potassium concentrations, and is sensitive to a variety of metabolic inhibitors. Also, amino acid uptake is depressed by actively transported sugars, and certain other amino acids, and is stimulated by phloridzin.Cells equilibrated with valine and loaded with 30 to 40mm intracellular sodium begin immediately to actively accumulate valine when suddenly introduced to media containing 20mm sodium. The cells establish a threefold gradient of amino acid during the interval when intracellular sodium is higher than extracellular sodium.Amino acid accumulation and²²Na efflux were monitored simultaneously in cells treated with phloridzin. While phloridzin causes a 30% stimulation of amino acid uptake, no variation in the rate of²²Na efflux or the steady-state level of²²Na maintained by the cells can be detected. Similarly, either 2.5mm glucose or 2.5mm 3-O-methylglucose cause approximately a 50% inhibition of 1mm valine uptake, but no detectable change in steady-state cellular²²Na content. Several aspects of the data seem inconsistent with concepts embodied in the ion gradient hypothesis, and it is suggested that a directly energized transport mechanism can better accommodate all of the data.     

Initial phases of DNA synthesis in Drosophila melanogaster

Replication patterns of the X chromosomes and autosomes in D. melanogaster male and female larvae during the discontinuously labeled initial and end phases of DNA synthesis were compared. In female larvae X and autosomes behaved correspondingly during all the replication stages. In males, however, the X chromosome shows a differential replication behavior from that of the autosomes already during the discontinuously labeled initial stage.—In those nuclei of both sexes, in which the autosomes correspond in their initial replication patterns, significantly more labeled regions are to be found over the male X than over the female X. The complementary behavior during the end phases (Berendes, 1966), i.e. the reverse of that above, leads to an earlier completion of the replication cycle in most of the labeled regions of the male X chromosome. The differential replication revealed in the autoradiograms is interpreted as a consequence of the polytene structure in giant chromosomes.     

Oncologic Trogocytosis of an Original Stromal Cells Induces Chemoresistance of Ovarian Tumours

Background

The microenvironment plays a major role in the onset and progression of metastasis. Epithelial ovarian cancer (EOC) tends to metastasize to the peritoneal cavity where interactions within the microenvironment might lead to chemoresistance. Mesothelial cells are important actors of the peritoneal homeostasis; we determined their role in the acquisition of chemoresistance of ovarian tumours.

Methodology/Principal Findings

We isolated an original type of stromal cells, referred to as “Hospicells” from ascitis of patients with ovarian carcinosis using limiting dilution. We studied their ability to confer chemoresistance through heterocellular interactions. These stromal cells displayed a new phenotype with positive immunostaining for CD9, CD10, CD29, CD146, CD166 and Multi drug resistance protein. They preferentially interacted with epithelial ovarian cancer cells. This interaction induced chemoresistance to platin and taxans with the implication of multi-drug resistance proteins. This contact enabled EOC cells to capture patches of the Hospicells membrane through oncologic trogocytosis, therefore acquiring their functional P-gp proteins and thus developing chemoresistance. Presence of Hospicells on ovarian cancer tissue micro-array from patients with neo-adjuvant chemotherapy was also significantly associated to chemoresistance.

Conclusions/Significance

This is the first report of trogocytosis occurring between a cancer cell and an original type of stromal cell. This interaction induced autonomous acquisition of chemoresistance. The presence of stromal cells within patient''s tumour might be predictive of chemoresistance. The specific interaction between cancer cells and stromal cells might be targeted during chemotherapy.