Cell migration: Fibroblasts find a new way to get ahead

Fibroblasts migrate on two-dimensional (2D) surfaces by forming lamellipodia—actin-rich extensions at the leading edge of the cell that have been well characterized. In this issue, Petrie et al. (2012. J. Cell Biol. http://dx.doi.org/10.1083/jcb.201201124) show that in some 3D environments, including tissue explants, fibroblasts project different structures, termed lobopodia, at the leading edge. Lobopodia still assemble focal adhesions; however, similar to membrane blebs, they are driven by actomyosin contraction and do not accumulate active Rac, Cdc42, and phosphatidylinositol 3-kinases

Navigating in tissue mazes: chemoattractant interpretation in complex environments.

Guided cell movement is essential for development and integrity of animals and crucially involved in cellular immune responses. Leukocytes are professional migratory cells that can navigate through most types of tissues and sense a wide range of directional cues. The responses of these cells to attractants have been mainly explored in tissue culture settings. How leukocytes make directional decisions in situ, within the challenging environment of a tissue maze, is less understood. Here we review recent advances in how leukocytes sense chemical cues in complex tissue settings and make links with paradigms of directed migration in development and Dictyostelium discoideum amoebae.This effort was supported by the Medical Research Council, UK, (MR/L019523/1 to M. Sarris) and the European Research Council (StG 281556 to M. Sixt).This is the final version of the article. It first appeared from Elsevier via http://dx.doi.org/10.1016/j.ceb.2015.08.00

Modelling adhesion-independent cell migration

A two-dimensional mathematical model for cells migrating without adhesion capabilities is presented and analyzed. Cells are represented by their cortex, which is modelled as an elastic curve, subject to an internal pressure force. Net polymerization or depolymerization in the cortex is modelled via local addition or removal of material, driving a cortical flow. The model takes the form of a fully nonlinear degenerate parabolic system. An existence analysis is carried out by adapting ideas from the theory of gradient flows. Numerical simulations show that these simple rules can account for the behavior observed in experiments, suggesting a possible mechanical mechanism for adhesion-independent motility.Comment: 22 pages and 9 figure

Navigating in tissue mazes: Chemoattractant interpretation in complex environments

Guided cell movement is essential for development and integrity of animals and crucially involved in cellular immune responses. Leukocytes are professional migratory cells that can navigate through most types of tissues and sense a wide range of directional cues. The responses of these cells to attractants have been mainly explored in tissue culture settings. How leukocytes make directional decisions in situ, within the challenging environment of a tissue maze, is less understood. Here we review recent advances in how leukocytes sense chemical cues in complex tissue settings and make links with paradigms of directed migration in development and Dictyostelium discoideum amoebae

IgM's exit route

The release of IgM is the first line of an antibody response and precedes the generation of high affinity IgG in germinal centers. Once secreted by freshly activated plasmablasts, IgM is released into the efferent lymph of reactive lymph nodes as early as 3 d after immunization. As pentameric IgM has an enormous size of 1,000 kD, its diffusibility is low, and one might wonder how it can pass through the densely lymphocyte-packed environment of a lymph node parenchyma in order to reach its exit. In this issue of JEM, Thierry et al. show that, in order to reach the blood stream, IgM molecules take a specific micro-anatomical route via lymph node conduits

Untersuchungen zum Nachweis und zum Vorkommen von Mykotoxinen und Hemmstoffen in Stutenmilch

Produktion, Vertrieb und Konsum von Stutenmilch spielt in Deutschland nur eine geringe Rolle. Der individuelle Verzehr kann jedoch recht hoch liegen (250 ml/Tag). Stutenmilch wird überwiegend über Direktvermarktung als tiefgefrorene Rohmilch vermarktet und unterliegt damit den Anforderungen an Vorzugsmilch. Darüber hinaus sind bezüglich Tierarzneimittelrückständen die Höchstmengen (VO 470/2009) sowie bezüglich der Mykotoxinen die Grenzwerte für Aflatoxin M1 einzuhalten. Für Stutenmilch liegen bisher bezüglich Tierarzneimittelrückständen keine und bezüglich des möglichen Vorkommens von Mykotoxinen fast keine Daten vor. Eine einfache Übertragung der für Kuhmilch gewonnenen Erkenntnisse auf die Stutenmilch ist aufgrund des unterschiedlichen Verdauungssystems nicht möglich. Auch die für Kuhmilch etablierten Analysensysteme sind nicht ohne weiteres zur Untersuchung von Stutenmilch einsetzbar, da sich die Milchzusammensetzung sehr unterscheidet. Daher wurde in der vorliegenden Arbeit zunächst ein modifiziertes Analysensystem für Hemmstoffe auf der Basis des Brillantschwarz-Reduktionstests etabliert. Zudem wurden Enzymimmuntests für folgende Mykotoxine zur Untersuchung von Stutenmilch etabliert: Aflatoxin M1, Ochratoxin A, T-2/HT-2 Toxin und Zearalenon. Untersuchungen auf das Fusarientoxin Deoxynivalenol, sowie zusätzliche Untersuchungen auf Zearalenon erfolgten mittels HPLC. Mit diesem Verfahren wurden im Zeitraum 2007/2008 insgesamt 53 Tankmilch-Proben von zwölf Stutenmilchbetrieben aus acht Bundesländern untersucht. Die Proben können als repräsentativ für die deutsche Stutenmilchproduktion angesehen werden. In keiner Probe wurden Hemmstoffe nachgewiesen (<4 µg/kg Penicillin G-Äquivalente). Ebenfalls nicht nachweisbar waren Aflatoxin M1 (<10 ng/kg) und Ochratoxin A (<15 ng/kg). Im Enzymimmuntest für Zearalenon ergaben zahlreiche Proben schwach positive Ergebnisse (200-400 ng/kg), die jedoch mittels HPLC (Nachweisgrenze 50 ng/kg) nicht bestätigt werden konnten. Bei einer realistischen und aus Sicht des Verbraucherschutzes ausreichenden Nachweisgrenze von 500 ng/kg waren alle Proben negativ für Zearalenon. Im Enzymimmuntest für T-2/HT-2 Toxin waren nach immunaffinitätschromatographischer Aufkonzentrierung in der Mehrzahl der Proben Spuren dieser Toxine im Bereich zehn bis 20 ng/kg nachweisbar. Deoxynivalenol war in zwei Proben in geringen Konzentrationen (2000-4000 ng/kg) nachweisbar, zwei weitere Proben wiesen Spuren dieses Toxins im Bereich der Nachweisgrenze (1000 ng/kg) auf. Deepoxynivalenol konnte nur in einer Probe in Spuren (circa 1000 ng/kg) nachgewiesen werden. Aufgrund dieser Befunde scheint Stutenmilch auch bei regelmäßigem Konsum keine relevante Aufnahmequelle für Antibiotikarückstände bzw. für die untersuchten Mykotoxine zu sein.Production and distribution of mares milk is of relatively minor importance in Germany. However, the individual daily consumption of persons preferring mare’s milk may be very high (250 ml/day). In Germany, mare´s milk is mainly sold as frozen raw milk via direct marketing channels. In contrast to milk from other species it is typically not heat treated, therefore specific regulations for certified raw milk apply here. Additionally, mare´s milk has to comply with regulations concerning contaminants, in particular mycotoxins (aflatoxin M1, AFM1) and concerning veterinary drug residues, such as antibiotics (VO 470/2009). Surprisingly, no studies exist until present concerning the carry-over of veterinary drugs into mare´s milk, and only one feeding study has been performed to estimate the carry-over of a mycotoxin (aflatoxin) from horse feed into milk. Simply conferring existing knowledge and carry-over data from cow’s milk on mare´s milk is not possible, because there are distinct differences between the digestive systems of both species. Additionally, analytical methods used to examine cow milk cannot be transferred to mare´s milk without further investigations. In the present thesis, a modified analytical method for inhibitor detection of veterinary drugs based on a BRT-inhibitor test was established. Additionally, enzyme immunoassay-based series of methods for several important mycotoxins, namely aflatoxin M1, ochratoxin A, T-2/HT-2 toxin, and zearalenone was optimized and validated for mare’s milk. Furthermore, deoxynivalenol/deepoxydeoxynivalenol (DON/DOM1) and zearalenone were analyzed by HPLC. A total of 53 bulk milk samples of mare´s milk from 12 different producers situated in eight federal states in Germany was analysed. Antimicrobial compounds exceeding the cut-off (4 &#956;g/kg Penicillin G-equivalents) were not detected in any of these samples. Likewise, all samples were free from detectable concentrations of aflatoxin M1 (<10 ng/kg) and ochratoxin A (<15 ng/kg). The enzyme immunoassay for zearalenone yielded weakly positive results (200-400 ng/kg) in a number of samples. However, these positive results could not be confirmed when using HPLC, which has a detection limit of 50 ng/kg. Using a realistic detection limit (500 ng/kg) which is considered as sufficient for zearalenone from a consumer’s protection point of view, all samples are negative for zearalenone. After purification and concentration of T-2/HT-2 toxin from mare’s milk using immunoaffinity columns, traces (10-20 ng/kg) of these toxins were found in the majority of the mare´s milk samples examined. Two samples were positive for DON at a level of 2000-4000 ng/kg and two at a level of 1000 ng/kg. Traces (1000 ng/kg) of deepoxynivalenol could only be detected in one sample. Since the analysed sample materials represent the majority of mare´s milk producers in Germany, these results indicate that the analyzed mycotoxins and antibiotics do not represent a problem in mare´s milk for humans even if consumed regularly

The cell sets the tone

In zebrafish larvae, it is the cell type that determines how the cell responds to a chemokine signal

Focal Adhesion-Independent Cell Migration.

Cell migration is central to a multitude of physiological processes, including embryonic development, immune surveillance, and wound healing, and deregulated migration is key to cancer dissemination. Decades of investigations have uncovered many of the molecular and physical mechanisms underlying cell migration. Together with protrusion extension and cell body retraction, adhesion to the substrate via specific focal adhesion points has long been considered an essential step in cell migration. Although this is true for cells moving on two-dimensional substrates, recent studies have demonstrated that focal adhesions are not required for cells moving in three dimensions, in which confinement is sufficient to maintain a cell in contact with its substrate. Here, we review the investigations that have led to challenging the requirement of specific adhesions for migration, discuss the physical mechanisms proposed for cell body translocation during focal adhesion-independent migration, and highlight the remaining open questions for the future

Mechanistic description of spatial processes using integrative modelling of noise-corrupted imaging data

Spatial patterns are ubiquitous on the subcellular, cellular and tissue level, and can be studied using imaging techniques such as light and fluorescence microscopy. Imaging data provide quantitative information about biological systems; however, mechanisms causing spatial patterning often remain elusive. In recent years, spatio-temporal mathematical modelling has helped to overcome this problem. Yet, outliers and structured noise limit modelling of whole imaging data, and models often consider spatial summary statistics. Here, we introduce an integrated data-driven modelling approach that can cope with measurement artefacts and whole imaging data. Our approach combines mechanistic models of the biological processes with robust statistical models of the measurement process. The parameters of the integrated model are calibrated using a maximum-likelihood approach. We used this integrated modelling approach to study in vivo gradients of the chemokine (C-C motif) ligand 21 (CCL21). CCL21 gradients guide dendritic cells and are important in the adaptive immune response. Using artificial data, we verified that the integrated modelling approach provides reliable parameter estimates in the presence of measurement noise and that bias and variance of these estimates are reduced compared to conventional approaches. The application to experimental data allowed the parametrization and subsequent refinement of the model using additional mechanisms. Among other results, model-based hypothesis testing predicted lymphatic vessel-dependent concentration of heparan sulfate, the binding partner of CCL21. The selected model provided an accurate description of the experimental data and was partially validated using published data. Our findings demonstrate that integrated statistical modelling of whole imaging data is computationally feasible and can provide novel biological insights