Self-organized biotectonics of termite nests.

The termite nest is one of the architectural wonders of the living world, built by the collective action of workers in a colony. Each nest has several characteristic structural motifs that allow for efficient ventilation, cooling, and traversal. We use tomography to quantify the nest architecture of the African termite Apicotermes lamani, consisting of regularly spaced floors connected by scattered linear and helicoidal ramps. To understand how these elaborate structures are built and arranged, we formulate a minimal model for the spatiotemporal evolution of three hydrodynamic fields-mud, termites, and pheromones-linking environmental physics to collective building behavior using simple local rules based on experimental observations. We find that floors and ramps emerge as solutions of the governing equations, with statistics consistent with observations of A. lamani nests. Our study demonstrates how a local self-reinforcing biotectonic scheme is capable of generating an architecture that is simultaneously adaptable and functional, and likely to be relevant for a range of other animal-built structures.

Thermostable designed ankyrin repeat proteins (DARPins) as building blocks for innovative drugs.

Designed ankyrin repeat proteins (DARPins) are antibody mimetics with high and mostly unexplored potential in drug development. By using in silico analysis and a rationally guided Ala scanning, we identified position 17 of the N-terminal capping repeat to play a key role in overall protein thermostability. The melting temperature of a DARPin domain with a single full-consensus internal repeat was increased by 8 °C to 10 °C when Asp17 was replaced by Leu, Val, Ile, Met, Ala, or Thr. We then transferred the Asp17Leu mutation to various backgrounds, including clinically validated DARPin domains, such as the vascular endothelial growth factor-binding domain of the DARPin abicipar pegol. In all cases, these proteins showed improvements in the thermostability on the order of 8 °C to 16 °C, suggesting the replacement of Asp17 could be generically applicable to this drug class. Molecular dynamics simulations showed that the Asp17Leu mutation reduces electrostatic repulsion and improves van-der-Waals packing, rendering the DARPin domain less flexible and more stable. Interestingly, this beneficial Asp17Leu mutation is present in the N-terminal caps of three of the five DARPin domains of ensovibep, a SARS-CoV-2 entry inhibitor currently in clinical development, indicating this mutation could be partly responsible for the very high melting temperature (>90 °C) of this promising anti-COVID-19 drug. Overall, such N-terminal capping repeats with increased thermostability seem to be beneficial for the development of innovative drugs based on DARPins.

Proteolysis-Targeting Chimeras Enhance T Cell Bispecific Antibody-Driven T Cell Activation and Effector Function through Increased MHC Class I Antigen Presentation in Cancer Cells.

The availability of Ags on the surface of tumor cells is crucial for the efficacy of cancer immunotherapeutic approaches using large molecules, such as T cell bispecific Abs (TCBs). Tumor Ags are processed through intracellular proteasomal protein degradation and are displayed as peptides on MHC class I (MHC I). Ag recognition through TCRs on the surface of CD8+ T cells can elicit a tumor-selective immune response. In this article, we show that proteolysis-targeting chimeras (PROTACs) that target bromo- and extraterminal domain proteins increase the abundance of the corresponding target-derived peptide Ags on MHC I in both liquid and solid tumor-derived human cell lines. This increase depends on the engagement of the E3 ligase to bromo- and extraterminal domain protein. Similarly, targeting of a doxycycline-inducible Wilms tumor 1 (WT1)-FKBP12F36V fusion protein, by a mutant-selective FKBP12F36V degrader, increases the presentation of WT1 Ags in human breast cancer cells. T cell-mediated response directed against cancer cells was tested on treatment with a TCR-like TCB, which was able to bridge human T cells to a WT1 peptide displayed on MHC I. FKBP12F36V degrader treatment increased the expression of early and late activation markers (CD69, CD25) in T cells; the secretion of granzyme ß, IFN-γ, and TNF-α; and cancer cell killing in a tumor-T cell coculture model. This study supports harnessing targeted protein degradation in tumor cells, for modulation of T cell effector function, by investigating for the first time, to our knowledge, the potential of combining a degrader and a TCB in a cancer immunotherapy setting.

Neoadjuvant Chemotherapy in Pancreatic Cancer: An Appraisal of the Current High-Level Evidence.

At the time of diagnosis, only about 20% of patients with pancreatic ductal adenocarcinoma (PDAC) have resectable disease. PDAC treatment necessitates a multidisciplinary approach, and adjuvant chemotherapy after upfront resection is an established means of preventing recurrence. Neoadjuvant chemotherapy (NAT), originally introduced to downstage tumor size, is nowadays more frequently used for selection of patients with favorable tumor biology and to control potential micrometastases. While NAT is routinely applied in locally advanced (LA) PDAC, there is increasing evidence demonstrating benefits of NAT in borderline resectable (BR) PDAC. The concept of NAT has recently been tested in resectable PDAC, but to date NAT has been restricted to clinical trials, as the data are limited and no clear benefits have yet been shown in this patient group. This review summarizes the current evidence for NAT in resectable, BR, and LA PDAC, with a focus on high-level evidence and randomized controlled trials.

Stigmergic construction and topochemical information shape ant nest architecture.

The nests of social insects are not only impressive because of their sheer complexity but also because they are built from individuals whose work is not centrally coordinated. A key question is how groups of insects coordinate their building actions. Here, we use a combination of experimental and modeling approaches to investigate nest construction in the ant Lasius niger. We quantify the construction dynamics and the 3D structures built by ants. Then, we characterize individual behaviors and the interactions of ants with the structures they build. We show that two main interactions are involved in the coordination of building actions: (i) a stigmergic-based interaction that controls the amplification of depositions at some locations and is attributable to a pheromone added by ants to the building material; and (ii) a template-based interaction in which ants use their body size as a cue to control the height at which they start to build a roof from existing pillars. We then develop a 3D stochastic model based on these individual behaviors to analyze the effect of pheromone presence and strength on construction dynamics. We show that the model can quantitatively reproduce key features of construction dynamics, including a large-scale pattern of regularly spaced pillars, the formation and merging of caps over the pillars, and the remodeling of built structures. Finally, our model suggests that the lifetime of the pheromone is a highly influential parameter that controls the growth and form of nest architecture.

Do ants need to estimate the geometrical properties of trail bifurcations to find an efficient route? A swarm robotics test bed.

Interactions between individuals and the structure of their environment play a crucial role in shaping self-organized collective behaviors. Recent studies have shown that ants crossing asymmetrical bifurcations in a network of galleries tend to follow the branch that deviates the least from their incoming direction. At the collective level, the combination of this tendency and the pheromone-based recruitment results in a greater likelihood of selecting the shortest path between the colony's nest and a food source in a network containing asymmetrical bifurcations. It was not clear however what the origin of this behavioral bias is. Here we propose that it results from a simple interaction between the behavior of the ants and the geometry of the network, and that it does not require the ability to measure the angle of the bifurcation. We tested this hypothesis using groups of ant-like robots whose perceptual and cognitive abilities can be fully specified. We programmed them only to lay down and follow light trails, avoid obstacles and move according to a correlated random walk, but not to use more sophisticated orientation methods. We recorded the behavior of the robots in networks of galleries presenting either only symmetrical bifurcations or a combination of symmetrical and asymmetrical bifurcations. Individual robots displayed the same pattern of branch choice as individual ants when crossing a bifurcation, suggesting that ants do not actually measure the geometry of the bifurcations when travelling along a pheromone trail. Finally at the collective level, the group of robots was more likely to select one of the possible shorter paths between two designated areas when moving in an asymmetrical network, as observed in ants. This study reveals the importance of the shape of trail networks for foraging in ants and emphasizes the underestimated role of the geometrical properties of transportation networks in general.

DARPin-targeting of measles virus: unique bispecificity, effective oncolysis, and enhanced safety.

Oncolytic virotherapy is an emerging treatment modality that uses replication-competent viruses to destroy cancers. Many naturally occurring viruses have a preferential, although nonexclusive, tropism for tumors and tumor cells. In addition, specific targeting of cancer cells can be achieved at the virus entry level. We optimized retargeting of cell entry by elongating the measles virus attachment protein with designed ankyrin repeat proteins (DARPins), while simultaneously ablating entry through the natural receptors. DARPin-targeted viruses were strongly attenuated in off-target tissue, thereby enhancing safety, but completely eliminated tumor xenografts. Taking advantage of the unique properties of DARPins of being fused without generating folding problems, we generated a virus simultaneous targeting two different tumor markers. The bispecific virus retained the original oncolytic efficacy, while providing proof of concept for a strategy to counteract issues of resistance development. Thus, DARPin-targeting opens new prospects for the development of personalized, targeted therapeutics.

Emergency cricothyroidotomy performed by inexperienced clinicians--surgical technique versus indicator-guided puncture technique.

BACKGROUND: To improve the ease and safety of cricothyroidotomy especially in the hand of the inexperienced, new instruments have been developed. In this study, we compared a new indicator-guided puncture technique (PCK) with standard surgical technique (ST) regarding success rate, performance time and complications. METHODS: Cricothyroidotomy in 30 human cadavers performed by 30 first year anaesthesia residents. The set chosen for use was randomised: PCK-technique (n=15) and ST (n=15). Success rates, insertion times and complications were compared. Traumatic lesions were anatomically confirmed after dissection. RESULTS: The ST-group had a higher success rate (100% vs 67%; p=0.04). There was no difference in time taken to complete the procedure (PCK 82 s. vs ST 95 s.; p=0.89). There was a higher complication rate in the PCK-group (67% vs 13%; p=0.04). Most frequent complication in the PCK-group was injury to the posterior tracheal wall (n=8), penetration to the oesophageal lumen (n=4) and injury to the thyroid and/or cricoid cartilage (n=5). In the ST-group in only 2 cases minor complications were observed (small vessel injury). CONCLUSIONS: In this human cadaver study the PCK technique produced more major complications and more failures than the ST. In the hand of the inexperienced operator the standard surgical approach seems to be a safe procedure, which can successfully be performed within an adequate time. The PCK technique cannot be recommended for inexperienced operators.

New laser soldering-based closures: a promising method in natural orifice transluminal endoscopic surgery.

BACKGROUND: Complete closure of gastrotomy is the linchpin of safe natural orifice transgastric endoscopic surgery. OBJECTIVE: To evaluate feasibility and efficacy of a new method of gastrotomy closure by using a sutureless laser tissue-soldering (LTS) technique in an ex vivo porcine stomach. DESIGN: In vitro experiment. SETTING: Experimental laboratory. INTERVENTIONS: Histological analysis and internal and external liquid pressure with and without hydrochloric acid exposure were determined comparing gastrotomy closure with LTS and with hand-sewn surgical sutures. MAIN OUTCOME MEASUREMENTS: Comparison of LTS and hand-sewn surgical gastrotomy closure. The primary outcome parameter was the internal leak pressure. Secondary parameters were the difference between internal and external leak pressures, the impact of an acid environment on the device, histological changes, and feasibility of endoscopic placement. RESULTS: The internal liquid leak pressure after LTS was almost twice as high as after hand-sewn surgical closure (416 ± 53 mm Hg vs 229 ± 99 mm Hg; P = .01). The internal leak pressure (416 ± 53 mm Hg) after LTS was higher than the external leak pressure (154 ± 46 mm Hg; P < .0001). An acidic environment did not affect leak pressure after LTS. Endoscopic LTS closure was feasible in all experiments. Histopathology revealed only slight alterations beneath the soldering plug. LIMITATIONS: In vitro experiments. CONCLUSIONS: Leak pressure after LTS closure of gastrotomy is higher than after hand-sewn surgical closure. LTS is a promising technique for closure of gastrotomies and iatrogenic perforations. Further experiments, in particular survival studies, are mandatory.

DARPins: an efficient targeting domain for lentiviral vectors.

We have recently developed a retargeting system for lentiviral vectors (LVs) that relies on the pseudotyping of LVs with engineered measles virus (MV) glycoproteins (hemagglutinin (H) and fusion protein (F)). Specificity is provided through display of a single-chain antibody (scFv) as targeting domain by fusion to the MV-H protein. As an alternative to scFv, designed ankyrin repeat proteins (DARPins) can be selected to become high-affinity binders to any kind of target molecule. In this study six HER2/neu-specific DARPins exhibiting different affinities and binding to different HER2/neu epitopes were applied as targeting domains. All H-DARPin fusion proteins were efficiently expressed on the cell surface. Upon coexpression with F, syncytia formation was observed in HER2/neu positive cells only and correlated directly with the HER2/neu receptor density. All H-DARPin proteins incorporated into LVs, albeit at different levels. The vectors only transduced HER2/neu-positive cells, while HER2/neu-negative cells remained untransduced. Highest titers were observed with one particular DARPin binding to the membrane distal domain of HER2/neu with medium affinity. When applied in vivo systemically, HER2/neu-targeted LVs showed exclusive gene expression in HER2/neu positive tumor tissue, while vesicular stomatitis virus-glycoprotein (VSV-G) pseudotyped vectors mainly transduced cells in spleen and liver. Thus, DARPins are a promising alternative to scFvs for retargeting of LVs.

Chimeric antigen receptor T cells engineered to recognize the P329G-mutated Fc part of effector-silenced tumor antigen-targeting human IgG1 antibodies enable modular targeting of solid tumors.

BACKGROUND: Chimeric antigen receptor (CAR) T cell therapy has proven its clinical utility in hematological malignancies. Optimization is still required for its application in solid tumors. Here, the lack of cancer-specific structures along with tumor heterogeneity represent a critical barrier to safety and efficacy. Modular CAR T cells indirectly binding the tumor antigen through CAR-adaptor molecules have the potential to reduce adverse events and to overcome antigen heterogeneity. We hypothesized that a platform utilizing unique traits of clinical grade antibodies for selective CAR targeting would come with significant advantages. Thus, we developed a P329G-directed CAR targeting the P329G mutation in the Fc part of tumor-targeting human antibodies containing P329G L234A/L235A (LALA) mutations for Fc silencing. METHODS: A single chain variable fragment-based second generation P329G-targeting CAR was retrovirally transduced into primary human T cells. These CAR T cells were combined with IgG1 antibodies carrying P329G LALA mutations in their Fc part targeting epidermal growth factor receptor (EGFR), mesothelin (MSLN) or HER2/neu. Mesothelioma, pancreatic and breast cancer cell lines expressing the respective antigens were used as target cell lines. Efficacy was evaluated in vitro and in vivo in xenograft mouse models. RESULTS: Unlike CD16-CAR T cells, which bind human IgG in a non-selective manner, P329G-targeting CAR T cells revealed specific effector functions only when combined with antibodies carrying P329G LALA mutations in their Fc part. P329G-targeting CAR T cells cannot be activated by an excess of human IgG. P329G-directed CAR T cells combined with a MSLN-targeting P329G-mutated antibody mediated pronounced in vitro and in vivo antitumor efficacy in mesothelioma and pancreatic cancer models. Combined with a HER2-targeting antibody, P329G-targeting CAR T cells showed substantial in vitro activation, proliferation, cytokine production and cytotoxicity against HER2-expressing breast cancer cell lines and induced complete tumor eradication in a breast cancer xenograft mouse model. The ability of the platform to target multiple antigens sequentially was shown in vitro and in vivo. CONCLUSIONS: P329G-targeting CAR T cells combined with antigen-binding human IgG1 antibodies containing the P329G Fc mutation mediate pronounced in vitro and in vivo effector functions in different solid tumor models, warranting further clinical translation of this concept.

Endosonographic radial tumor thickness after neoadjuvant chemoradiation therapy to predict response and survival in patients with locally advanced esophageal cancer: a prospective multicenter phase ll study by the Swiss Group for Clinical Cancer Research (SAKK 75/02).

BACKGROUND: EUS response assessment in patients with locally advanced esophageal cancer undergoing neoadjuvant chemoradiation therapy (CRT) is limited by disintegration of the involved anatomic structures. OBJECTIVE: Predictive and prognostic values of a prospectively defined maximum tumor thickness (MTT). DESIGN: Prospective open-label phase ll study (SAKK 75/02). SETTING: Multicenter, nationwide. PATIENTS: Of 66 patients with primary CRT, 56 underwent en bloc esophagectomy. INTERVENTIONS: EUS-measured MTT before and 2-5 weeks after CRT (yMTT). MAIN OUTCOME MEASUREMENTS: Cutoffs: (1) absolute thickness (yMTT) after CRT < or = 6 mm; (2) relative reduction compared with baseline (ratio yMTT/MTT) < or = 50%. Correlation between EUS measurements and histopathologic tumor regression grade (TRG) and overall survival (OS). RESULTS: Sixteen of 56 patients were not included for EUS evaluation (10 severe stenosis, 5 MTT not measured, 1 intolerance to second EUS). Characteristics (n = 40) were as follow: median age, 60 years; squamous cell carcinoma, 42%; and adenocarcinoma (AC), 58%. Initial stage was: 10 T2N1, 3 T3N0, 26 T3N1, 1 T3Nx; 14 of 23 AC Siewert type 1. Wilcoxon rank sum test showed significant correlation of TRG1 with yMTT < or = 6 mm (P = .008) and yMTT/MTT < or = 50% (P = .003). The effect of yMTT on TRG1 was significant (P = .0193; odds ratio, 0.687 [95% CI, 0.502-0.941]). The predefined cutoff of < or = 6 mm for yMTT was predictive for TRG1 (P = .0037; Fisher exact test). After a median follow-up of 28.6 months, there was a clear trend for benefit in OS with yMTT < or = 6 mm and yMTT/MTT < or = 50%. LIMITATIONS: Small sample size. CONCLUSION: In a multicenter setting, MTT measured by EUS after CRT was highly predictive for response and showed a clear trend for predicting survival.

CAR-J cells for antibody discovery and lead optimization of TCR-like immunoglobulins.

T-cell bispecific antibodies (TCBs) are a novel class of engineered immunoglobulins that unite monovalent binding to the T-cell receptor (TCR) CD3e chain and bivalent binding to tumor-associated antigens in order to recruit and activate T-cells for tumor cell killing. In vivo, T-cell activation is usually initiated via the interaction of the TCR with the peptide-HLA complex formed by the human leukocyte antigen (HLA) and peptides derived from intracellular proteins. TCR-like antibodies (TCRLs) that recognize pHLA-epitopes extend the target space of TCBs to peptides derived from intracellular proteins, such as those overexpressed during oncogenesis or created via mutations found in cancer. One challenge during lead identification of TCRL-TCBs is to identify TCRLs that specifically, and ideally exclusively, recognize the desired pHLA, but not unrelated pHLAs. In order to identify TCRLs suitable for TCRL-TCBs, large numbers of TCRLs have to be tested in the TCB format. Here, we propose a novel approach using chimeric antigen receptors (CARs) to facilitate the identification of highly selective TCRLs. In this new so-called TCRL-CAR-J approach, TCRL-candidates are transduced as CARs into Jurkat reporter-cells, and subsequently assessed for their specificity profile. This work demonstrates that the CAR-J reporter-cell assay can be applied to predict the profile of TCRL-TCBs without the need to produce each candidate in the final TCB format. It is therefore useful in streamlining the identification of TCRL-TCBs.

Dendritic cells dictate responses to PD-L1 blockade cancer immunotherapy.

PD-L1/PD-1 blocking antibodies have demonstrated therapeutic efficacy across a range of human cancers. Extending this benefit to a greater number of patients, however, will require a better understanding of how these therapies instigate anticancer immunity. Although the PD-L1/PD-1 axis is typically associated with T cell function, we demonstrate here that dendritic cells (DCs) are an important target of PD-L1 blocking antibody. PD-L1 binds two receptors, PD-1 and B7.1 (CD80). PD-L1 is expressed much more abundantly than B7.1 on peripheral and tumor-associated DCs in patients with cancer. Blocking PD-L1 on DCs relieves B7.1 sequestration in cis by PD-L1, which allows the B7.1/CD28 interaction to enhance T cell priming. In line with this, in patients with renal cell carcinoma or non-small cell lung cancer treated with atezolizumab (PD-L1 blockade), a DC gene signature is strongly associated with improved overall survival. These data suggest that PD-L1 blockade reinvigorates DC function to generate potent anticancer T cell immunity.

Combining the best of two worlds: highly flexible chimeric antigen receptor adaptor molecules (CAR-adaptors) for the recruitment of chimeric antigen receptor T cells.

Chimeric antigen receptor (CAR)-engineered T cells have a proven efficacy for the treatment of refractory hematological B cell malignancies. While often accompanied by side effects, CAR-T technology is getting more mature and will become an important treatment option for various tumor indications. In this review, we summarize emerging approaches that aim to further evolve CAR-T cell therapy based on combinations of so-called universal or modular CAR-(modCAR-)T cells, and their respective adaptor molecules (CAR-adaptors), which mediate the crosslinking between target and effector cells. The activity of such modCAR-T cells is entirely dependent on binding of the respective CAR-adaptor to both a tumor antigen and to the CAR-expressing T cell. Contrary to conventional CAR-T cells, where the immunological synapse is established by direct interaction of CAR and membrane-bound target, modCAR-T cells provide a highly flexible and customizable development of the CAR-T cell concept and offer an additional possibility to control T cell activity.

The architectural design of smart ventilation and drainage systems in termite nests.

Termite nests have been widely studied as effective examples for ventilation and thermoregulation. However, the mechanisms by which these properties are controlled by the microstructure of the outer walls remain unclear. Here, we combine multiscale X-ray imaging with three-dimensional flow field simulations to investigate the impact of the architectural design of nest walls on CO2 exchange, heat transport and water drainage. We show that termites build outer walls that contain both small and percolating large pores at the microscale. The network of larger microscale pores enhances permeability by one to two orders of magnitude compared to the smaller pores alone, and it increases CO2 diffusivity up to eight times. In addition, the pore network offers enhanced thermal insulation and allows quick drainage of rainwater, thereby restoring the ventilation and providing structural stability to the wet nest.

P329G-CAR-J: a novel Jurkat-NFAT-based CAR-T reporter system recognizing the P329G Fc mutation.

Monoclonal antibody-based therapeutics are an integral part of treatment of different human diseases, and the selection of suitable antibody candidates during the discovery phase is essential. Here, we describe a novel, cellular screening approach for the identification and characterization of therapeutic antibodies suitable for conversion into T cell bispecific antibodies using chimeric antigen receptor (CAR) transduced Jurkat-NFAT-luciferase reporter cells (CAR-J). For that purpose, we equipped a Jurkat-NFAT reporter cell line with a universal CAR, based on a monoclonal antibody recognizing the P329G mutation in the Fc-part of effector-silenced human IgG1-antibodies. In addition to scFv-based second generation CARs, Fab-based CARs employing the P329G-binder were generated. Using these anti-P329G-CAR-J cells together with the respective P329G-mutated IgG1-antibodies, we established a system, which facilitates the rapid testing of therapeutic antibody candidates in a flexible, high throughput setting during early stage discovery. We show that both, scFv- and Fab-based anti-P329G-CAR-J cells elicit a robust and dose-dependent luciferase signal if the respective antibody acts as an adaptor between tumor target and P329G-CAR-J cells. Importantly, we could demonstrate that functional characteristics of the antibody candidates, derived from the anti-P329G-CAR-J screening assay, are predictive for the functionality of these antibodies in the T cell bispecific antibody format.

Marine biodiversity from zero to a thousand meters at Clipperton Atoll (Île de La Passion), Tropical Eastern Pacific.

Clipperton Atoll (Île de La Passion) is the only atoll in the Tropical Eastern Pacific (TEP) ecoregion and, owing to its isolation, possesses several endemic species and is likely an important stepping stone between Oceania, the remainder of the TEP, including other oceanic islands and the west coast of Central America. We describe the biodiversity at this remote atoll from shallow water to depths greater than one thousand meters using a mixture of technologies (SCUBA, stereo baited remote underwater video stations, manned submersible, and deep-sea drop cameras). Seventy-four unique taxa of invertebrates were identified during our expedition. The majority (70%) of these taxa were confined to the top 400 m and consisted mostly of sessile organisms. Decapod crustaceans and black corals (Antipatharia) had the broadest depth ranges, 100-1,497 m and 58-967 m, respectively. Decapods were correlated with the deepest depths, while hard corals were correlated with the shallow depths. There were 96 different fish taxa from 41 families and 15 orders, of which 70% were restricted to depths <200 m. While there was a decreasing trend in richness for both fish and invertebrate taxa with depth, these declines were not linear across the depth gradient. Instead, peaks in richness at ∼200 m and ∼750 m coincided with high turnover due to the appearance of new taxa and disappearance of other taxa within the community and is likely associated with the strong oxygen minimum zone that occurs within the region. The overall depth effect was stronger for fishes compared with invertebrates, which may reflect ecological preferences or differences in taxonomic resolution among groups. The creation of a no-take marine reserve 12 nautical miles around the atoll in 2016 will help conserve this unique and relatively intact ecosystem, which possesses high predator abundance.

The interplay between a self-organized process and an environmental template: corpse clustering under the influence of air currents in ants.

Many spatial patterns observed in nature emerge from local processes and their interactions with the local environment. The clustering of objects by social insects represents such a pattern formation process that can be observed at both the individual and the collective level. In this paper, we study the interaction between air currents and clustering behaviour in order to address the coordinating mechanisms at the individual level that underlie the spatial pattern formation process in a heterogeneous environment. We choose the corpse clustering behaviour of the ant Messor sanctus as an experimental paradigm. In a specifically designed experimental set-up with a well-controlled laminar air flow (approx. 1 cm s-1), we first quantify the modulation of the individual corpse aggregation behaviour as a function of corpse density, air flow intensity and the ant's position with respect to corpse piles and air flow direction. We then explore by numerical simulation how the forming corpse piles modify the laminar air flow around them and link this result with the individual behaviour modulation. Finally, we demonstrate on the collective level that this laminar air flow leads to an elongation and a slow displacement of the formed corpse piles in the direction of the air current. Both the individual behaviour modulated by air flow and the air flow modulated by the forming corpse piles can explain the pile patterns observed on the collective level as a stigmergic process. We discuss the generality of this coordinating mechanism to explain the clustering phenomena in heterogeneous environments reported in the literature.

Rigidity of the extracellular part of HER2: Evidence from engineering subdomain interfaces and shared-helix DARPin-DARPin fusions.

The second member of the human ErbB family of receptor tyrosine kinases, HER2/hErbB2, is regarded as an exceptional case: The four extracellular subdomains could so far only be found in one fixed overall conformation, designated "open" and resembling the ligand-bound form of the other ErbB receptors. It thus appears to be different from the extracellular domains of the other family members that show inter-subdomain flexibility and exist in a "tethered" form in the absence of ligand. For HER2, there was so far no direct evidence for such a tethered conformation on the cell surface. Nonetheless, alternative conformations of HER2 in vivo could so far not be excluded. We now demonstrate the rigidity of HER2 on the surface of tumor cells by employing two orthogonal approaches of protein engineering: To directly test the potential of the extracellular domain of HER2 to adopt a pseudo-tethered conformation on the cell surface, we first designed HER2 variants with a destabilized interface between extracellular subdomains I and III that would favor deviation from the "open" conformation. Secondly, we used differently shaped versions of a Designed Ankyrin Repeat Protein (DARPin) fusion, recognizing subdomain I of HER2, devised to work as probes for a putative pseudo-tethered extracellular domain of HER2. Combining our approaches, we exclude, on live cells and in vitro, that significant proportions of HER2 deviate from the "open" conformation.