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Chemotaxis, where cell movement is steered by chemical gradients, is a widespread and essential way of organising cell behaviour. But where do the instructions come from - who makes gradients, and how are they controlled? We discuss the emerging concept that chemotactic cells often create attractant gradients at the same time as responding to them. This self-guidance is more robust, works across greater distances, and is more informative about the local environment than passive responses. Several mechanisms can establish autonomous gradients. Best known are self-generated gradients, in which the cells degrade a widespread attractant, but cells also produce repellents and 'relay' by secreting fresh attractant after stimulation. Understanding how cells make and interpret their own chemoattractant gradients is fundamental to understanding the spatial patterns seen in all organisms., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

The crawling behavior of leukocytes is driven by the cell morphology transition, which is a direct manifestation of molecular motor machinery. The topographical anisotropy and mechanical stiffness of the substrates are the main physical cues that affect leukocytes' shape generation and migratory responses. However, their combined effects on the cell morphology and motility have been poorly understood, particularly for neutrophils, which are the fastest reacting leukocytes against infections and wounds. Here, spatiotemporally correlated physical parameters are shown, which determine the neutrophil shape change during migratory processes, in response to surface topography and elasticity. Guided crawling and shape generation of individual neutrophils, activated by a uniform concentration of a chemoattractant, are analyzed by adopting elasticity-tunable micropatterning and live cell imaging techniques. Whole cell-level image analysis is performed based on a planar geometric quantification of cell shape and motility. The findings show that the pattern anisotropy and elastic modulus of the substrate induce synergic effects on the shape anisotropy, deformability, and polarization/alignment of crawling neutrophils. How the morphology-motility relationship is affected by different surface microstructures and stiffness is demonstrated. These results imply that the neutrophil shape-motility correlations can be utilized for controlling the immune cell functions with predefined physical microenvironments., (© 2022 Wiley-VCH GmbH.)

Chemotaxis identification is very important for the research and application of rhizosphere growth-promoting bacteria. We established a straightforward method to quickly identify the chemoattractants that could induce the chemotactic movement of rhizosphere growth-promoting bacteria on sterile glass slides via simple steps. Bacteria solution (OD600 = 0.5) and sterile chemoattractant aqueous solution were added dropwise on the glass slide at an interval of 1 cm. An inoculating loop was used to connect the chemoattractant aqueous solution to the bacterial solution. The slide was kept at room temperature for 20 min on the clean bench. Finally, the chemoattractant aqueous solution was collected for bacterial counting and microscopic observation. In this study, through multiple comparisons of experimental results, the method overcame multiple shortcomings of traditional bacterial chemotaxis methods. The method reduced the error of plate counting and shortened the experimental cycle. For the identification of chemoattractant substances, this new method can save 2-3 days compared to the traditional method. Additionally, this method allows any researcher to systematically complete a bacterial chemotaxis experiment within 1-2 days. The protocol can be considered a valuable resource for understanding plant-microbe interactions.

A GPCR-mediated signaling network enables a chemotactic cell to generate adaptative Ras signaling in response to a large range of concentrations of a chemoattractant. To explore potential regulatory mechanisms of GPCR-controlled Ras signaling in chemosensing, we applied a software package, Simmune, to construct detailed spatiotemporal models simulating responses of the cAR1-mediated Ras signaling network. We first determined the dynamics of G-protein activation and Ras signaling in Dictyostelium cells in response to cAMP stimulations using live-cell imaging and then constructed computation models by incorporating potential mechanisms. Using simulations, we validated the dynamics of signaling events and predicted the dynamic profiles of those events in the cAR1-mediated Ras signaling networks with defective Ras inhibitory mechanisms, such as without RasGAP, with RasGAP overexpression, or with RasGAP hyperactivation. We describe a method of using Simmune to construct spatiotemporal models of a signaling network and run computational simulations without writing mathematical equations. This approach will help biologists to develop and analyze computational models that parallel live-cell experiments.

The pathogen Staphylococcus aureus can readily develop antibiotic resistance and evade the human immune system, which is associated with reduced levels of neutrophil recruitment. Here, we present a class of antibacterial peptides with potential to act both as antibiotics and as neutrophil chemoattractants. The compounds, which we term 'antibiotic-chemoattractants', consist of a formylated peptide (known to act as chemoattractant for neutrophil recruitment) that is covalently linked to the antibiotic vancomycin (known to bind to the bacterial cell wall). We use a combination of in vitro assays, cellular assays, infection-on-a-chip and in vivo mouse models to show that the compounds improve the recruitment, engulfment and killing of S. aureus by neutrophils. Furthermore, optimizing the formyl peptide sequence can enhance neutrophil activity through differential activation of formyl peptide receptors. Thus, we propose antibiotic-chemoattractants as an alternate approach for antibiotic development., (© 2021. The Author(s).)

During the last decade, a consensus has emerged that the stochastic triggering of an excitable system drives pseudopod formation and subsequent migration of amoeboid cells. The presence of chemoattractant stimuli alters the threshold for triggering this activity and can bias the direction of migration. Though noise plays an important role in these behaviors, mathematical models have typically ignored its origin and merely introduced it as an external signal into a series of reaction-diffusion equations. Here we consider a more realistic description based on a reaction-diffusion master equation formalism to implement these networks. In this scheme, noise arises naturally from a stochastic description of the various reaction and diffusion terms. Working on a three-dimensional geometry in which separate compartments are divided into a tetrahedral mesh, we implement a modular description of the system, consisting of G-protein coupled receptor signaling (GPCR), a local excitation-global inhibition mechanism (LEGI), and signal transduction excitable network (STEN). Our models implement detailed biochemical descriptions whenever this information is available, such as in the GPCR and G-protein interactions. In contrast, where the biochemical entities are less certain, such as the LEGI mechanism, we consider various possible schemes and highlight the differences between them. Our simulations show that even when the LEGI mechanism displays perfect adaptation in terms of the mean level of proteins, the variance shows a dose-dependence. This differs between the various models considered, suggesting a possible means for determining experimentally among the various potential networks. Overall, our simulations recreate temporal and spatial patterns observed experimentally in both wild-type and perturbed cells, providing further evidence for the excitable system paradigm. Moreover, because of the overall importance and ubiquity of the modules we consider, including GPCR signaling and adaptation, our results will be of interest beyond the field of directed migration., Competing Interests: The authors have declared that no competing interests exist.

Anti-cancer T-cell responses are often halted due to the immune-suppressive micro-environment, in part related to tumor-associated macrophages. In the current study, we assessed indigestible β-glucans (oatβG, curdlan, grifolan, schizophyllan, lentinan, yeast whole glucan particles (yWGP), zymosan and two additional yeast-derived β-glucans a and b) for their physicochemical properties as well as their effects on the plasticity of human monocyte-derived macrophages that were polarized with IL-4 to immune-suppressive macrophages. Beta-glucans were LPS/LTA free, and tested for solubility, molecular masses, protein and monosaccharide contents. Curdlan, yeast-b and zymosan re-polarized M(IL-4) macrophages towards an M1-like phenotype, in particular showing enhanced gene expression of CCR7, ICAM1 and CD80, and secretion of TNF-α and IL-6. Notably, differential gene expression, pathway analysis as well as protein expressions demonstrated that M(IL-4) macrophages treated with curdlan, yeast-b or zymosan demonstrated enhanced production of chemo-attractants, such as CCL3, CCL4, and CXCL8, which contribute to recruitment of monocytes and neutrophils. The secretion of chemo-attractants was confirmed when using patient-derived melanoma-infiltrating immune cells. Taken together, the bacterial-derived curdlan as well as the yeast-derived β-glucans yeast-b and zymosan have the unique ability to preferentially skew macrophages towards a chemo-attractant-producing phenotype that may aid in anti-cancer immune responses.

The human leukemia cell line (HL-60) is an alternative to primary neutrophils in research studies. However, because HL-60 cells proliferate in an incompletely differentiated state, they must undergo differentiation before they acquire the functional properties of neutrophils. Here we provide evidence of swarming and chemotaxis in differentiated HL-60 neutrophil-like cells (dHL-60) using precise microfluidic assays. We found that dimethyl sulfoxide differentiated HL-60 cells (DdHL-60) have a larger size, increased length, and lower ability to squeeze through narrow channels compared to primary neutrophils. They migrate through tapered microfluidic channels slower than primary neutrophils, but faster than HL-60s differentiated by other protocols, e.g., using all-trans retinoic acid. We found that dHL-60 can swarm toward zymosan particle clusters, though they display disorganized migratory patterns and produce swarms of smaller size compared to primary neutrophils.

Cells of the social amoeba Dictyostelium discoideum migrate to a source of periodic traveling waves of chemoattractant as part of a self-organized aggregation process. An important part of this process is cellular memory, which enables cells to respond to the front of the wave and ignore the downward gradient in the back of the wave. During this aggregation, the background concentration of the chemoattractant gradually rises. In our microfluidic experiments, we exogenously applied periodic waves of chemoattractant with various background levels. We find that increasing background does not make detection of the wave more difficult, as would be naively expected. Instead, we see that the chemotactic efficiency significantly increases for intermediate values of the background concentration but decreases to almost zero for large values in a switch-like manner. These results are consistent with a computational model that contains a bistable memory module, along with a nonadaptive component. Within this model, an intermediate background level helps preserve directed migration by keeping the memory activated, but when the background level is higher, the directional stimulus from the wave is no longer sufficient to activate the bistable memory, suppressing directed migration. These results suggest that raising levels of chemoattractant background may facilitate the self-organized aggregation in Dictyostelium colonies.

GPCR signaling is the most prevailing molecular mechanism for detecting ambient signals in eukaryotes. Chemotactic cells use GPCR signaling to process chemical cues for directional migration over a broad concentration range and with high sensitivity. Dictyostelium discoideum is a classical model, in which the molecular mechanism underlying eukaryotic chemotaxis has been well studied. Here, we describe protocols to evaluate the spatiotemporal chemotactic responses of Dictyostelium discoideum by different microscopic observations combined with biochemical assays. First, two different chemotaxis assays are presented to measure the dynamic concentration ranges for different cell strains or chemotactic parameters. Next, live-cell imaging and biochemical assays are provided to detect the activities of GPCR and its partner heterotrimeric G proteins upon chemoattractant stimulation. Finally, a method for detecting how a cell deciphers chemical gradients is described.

Rhus potaninii Maxim, a type of sumac, is an economically important tree widely cultivated in mountainous areas of western and central China. A gall, called the bellied gallnut, induced by the aphid, Kaburagia rhusicola Takagi, is important in the food, medical, and chemical industries in China. Volatiles from R. potaninii were found to attract K. rhusicola , but little is known about them. The chemical composition of these volatiles was investigated using GC-MS analysis and Y-tube olfactometer methods. Twenty-five compounds accounting for 55.3% of the volatiles were identified, with the highest proportion of 1-(4-ethylphenyl)ethanone (11.8%), followed by 1-(4-hydroxy-3-methylphenyl)ethanone (11.2%) and p -cymen-7-ol (7.1%). These findings provide a theoretical basis for the preparation of attractants and could eventually lead to increased bellied gallnut yield.

Soft tissue is composed of cells surrounded by an extracellular matrix that is made up of a diverse array of intricately organized proteins. These distinct components work in concert to maintain homeostasis and respond to tissue damage. During tissue repair, extracellular matrix proteins and their degradation products are known to influence physiological processes such as angiogenesis and inflammation. In this study we developed a discovery platform using a decellularized extracellular matrix biomaterial to identify new chemotrophic factors derived from the extracellular matrix. An in vitro culture of RAW.264 macrophage cells with the biomaterial ovine forestomach matrix led to the identification of a novel ~12 kDa chemotactic factor, termed 'MayDay', derived from the N-terminal 31-188 sequence of decorin. The recombinant MayDay protein was shown to be a chemotactic agent for mesenchymal stromal cells in vitro and in vivo. We hypothesize that the macrophage-induced cleavage of decorin, via MMP-12, leads to the release of the chemotactic molecule MayDay, that in turn recruits cells to the site of damaged tissue., Competing Interests: BCHM, RWFV and SGD are paid employees of Aroa Biosurgery Limited (Auckland, New Zealand). JS is a paid employee of Charles River (Freiburg, Germany). DGD and CHM are paid employees of Victoria University (Wellington, New Zealand). BCHM, SGD and CHM are shareholders of Aroa Biosurgery Limited. BCHM, SGD and DJD are listed as inventors on provisional patent U.S. Provisional Application No. 62/857,900, owned by Aroa Biosurgery Limited. BCHM is listed as inventor on patent US8415159B2, owned by Aroa Biosurgery Limited. Ovine forestomach matrix is manufactured by Aroa Biosurgery Limited and is available as commercial medical devices under the tradenames Endoform® Natural, Endoform® Antimicrobial, Myriad™, and Ovitex® distributed international by Aroa Biosurgery Limited This does not alter the authors adherence to PLOS ONE policies on sharing data and materials.

Neutrophils are frontline cells of the innate immune system. These effector leukocytes are equipped with intriguing antimicrobial machinery and consequently display high cytotoxic potential. Accurate neutrophil recruitment is essential to combat microbes and to restore homeostasis, for inflammation modulation and resolution, wound healing and tissue repair. After fulfilling the appropriate effector functions, however, dampening neutrophil activation and infiltration is crucial to prevent damage to the host. In humans, chemoattractant molecules can be categorized into four biochemical families, i.e., chemotactic lipids, formyl peptides, complement anaphylatoxins and chemokines. They are critically involved in the tight regulation of neutrophil bone marrow storage and egress and in spatial and temporal neutrophil trafficking between organs. Chemoattractants function by activating dedicated heptahelical G protein-coupled receptors (GPCRs). In addition, emerging evidence suggests an important role for atypical chemoattractant receptors (ACKRs) that do not couple to G proteins in fine-tuning neutrophil migratory and functional responses. The expression levels of chemoattractant receptors are dependent on the level of neutrophil maturation and state of activation, with a pivotal modulatory role for the (inflammatory) environment. Here, we provide an overview of chemoattractant receptors expressed by neutrophils in health and disease. Depending on the (patho)physiological context, specific chemoattractant receptors may be up- or downregulated on distinct neutrophil subsets with beneficial or detrimental consequences, thus opening new windows for the identification of disease biomarkers and potential drug targets.

A multifunctional motile microtrap is developed that is capable of autonomously attracting, trapping, and destroying pathogens by controlled chemoattractant and therapeutic agent release. The onion-inspired multi-layer structure contains a magnesium engine core and inner chemoattractant and therapeutic layers. Upon chemical propulsion, the magnesium core is depleted, resulting in a hollow structure that exposes the inner layers and serves as structural trap. The sequential dissolution and autonomous release of the chemoattractant and killing agents result in long-range chemotactic attraction, trapping, and destruction of motile pathogens. The dissolved chemoattractant (l-serine) significantly increases the accumulation and capture of motile pathogens (E. coli) within the microtrap structure, while the internal release of silver ions (Ag + ) leads to lysis of the pathogen accumulated within the microtrap cavity., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Mosquito-borne diseases like malaria are a major public health problem in tropical countries, such as Madagascar. Female Anopheles mosquito vectors the human malaria parasites (Plasmodium spp.) and is important indicator in malaria surveillance activities. Among the various means of vector control in Madagascar, the use of attractants for mass trapping of target species could be an alternative to insecticides. The aim of this study is to evaluate whether 4-hydroxycoumarin can be used as an attractant for anthropophilic Anopheles spp. vectors of malaria. For this, a field study was conducted using CDC light traps in the village of Ambohidray, Madagascar. 16 days of trapping was conducted and four replicates nights were performed for each product tested. 4-hydroxycoumarin, octenol and two types of blend of these products were tested. The results showed that 4-hydroxycoumarin (2 mg) have a significant attractive effect on Anopheles spp. and significant selectivity towards Anopheles gambiae s.l, and Anopheles mascarensis which are both significant malaria vectors in Madagascar. A synergy of 4-hydroxycoumarin with octenol was found to attract these mosquito vectors. A significant decrease in vector populations was observed during this experiment. These results suggest that 4-hydroxycoumarin could be useful for malaria surveillance and the control of vector populations.

The use of nanomaterials to regulate cell surface receptors is considered a novel strategy to manipulate cell behaviors. However, recognition is important to drive nanoparticle-cell complex formation. Here, we report a novel approach that uses graphene oxide (GO) as a chemoattractant to lure bacteria to nanosurface, facilitating complex formation. The amount of Escherichia coli ( E. coli ) cells attracted into capillaries containing 20 mg/L GO was more than 8.6-fold higher than that attracted into capillaries containing 20 mg/L glucose. The inherent mechanism involved interference with transmembrane chemoreceptors and activation of the chemotactic system via GO attachment and a subsequent increase in cell aggregation and migration via self-secreted quorum sensing molecules. The key feature of this strategy is the potential to improve the efficiency of the nanoparticle-cell recognition pattern and to expedite the development of surface-contact-related nanotechnology.

Here, a 3D printed multiplexed competitive migration assay is reported for characterizing a chemotactic response in the presence of multiple spatially distributed chemoattractants. The utility of the assay is demonstrated by examining the chemotactic response of human glioblastoma cells to spatially opposing chemotactic gradients of epidermal growth factor (EGF) and bradykinin (BK). Competitive migration assays involving spatially opposing gradients of EGF and BK that are optimized in the absence of the second chemoattractant show that 46% more glioblastoma cells migrate toward EGF sources. The migration velocities of human glioblastoma cells toward EGF and BK sources are reduced by 7.6 ± 2.2% and 11.6 ± 6.3% relative to those found in the absence of the spatially opposing chemoattractant. This work provides new insight to the chemotactic response associated with glioblastoma-vasculature interactions and a versatile, user-friendly platform for characterizing the chemotactic response of cells in the presence of multiple spatially distributed chemoattractants., (© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Tephritid fruit flies are amongst the most significant horticultural pests globally and male chemical lures are important for monitoring and control. Zingerone has emerged as a unique male fruit fly lure that can attract dacine fruit flies that are weakly or non-responsive to methyl eugenol and cuelure. However, the key features of zingerone that mediate this attraction are unknown. As Jarvis's fruit fly, Bactrocera jarvisi (Tryon), is strongly attracted to zingerone, we evaluated the response of B. jarvisi to 37 zingerone analogues in a series of field trials to elucidate the functional groups involved in attraction. The most attractive analogues were alkoxy derivatives, with isopropoxy being the most attractive, followed by ethoxy and trifluoromethoxy analogues. All of the phenolic esters tested were also attractive with the response typically decreasing with increasing size of the ester. Results indicate that the carbonyl group, methoxy group, and phenol of zingerone are key sites for the attraction of B. jarvisi and identify some constraints on the range of structural modifications that can be made to zingerone without compromising attraction. These findings are important for future work in developing and optimising novel male chemical lures for fruit flies.

Insects searching for resources are exposed to a complexity of mixed odours, often involving both attractant and repellent substances. Understanding how insects respond to this complexity of cues is crucial for understanding consumer-resource interactions, but also to develop novel tools to control harmful pests. To advance our understanding of insect responses to combinations of attractive and repellent odours, we formulated three qualitative hypotheses; the response-ratio hypothesis, the repellent-threshold hypothesis and the odour-modulation hypothesis. The hypotheses were tested by exposing Drosophila melanogaster in a wind tunnel to combinations of vinegar as attractant and four known repellents; benzaldehyde, 1-octen-3-ol, geosmin and phenol. The responses to benzaldehyde, 1-octen-3-ol and geosmin provided support for the response-ratio hypothesis, which assumes that the behavioural response depends on the ratio between attractants and repellents. The response to phenol, rather supported the repellent-threshold hypothesis, where aversion only occurs above a threshold concentration of the repellent due to overshadowing of the attractant. We hypothesize that the different responses may be connected to the localization of receptors, as receptors detecting phenol are located on the maxillary palps whereas receptors detecting the other odorants are located on the antennae.

GPR84 is an orphan G-protein-coupled receptor that is expressed on immune cells and implicated in several inflammatory diseases. The validation of GPR84 as a therapeutic target is hindered by the narrow range of available chemical tools and consequent poor understanding of GPR84 pathophysiology. Here we describe the discovery and characterization of DL-175, a potent, selective, and structurally novel GPR84 agonist and the first to display significantly biased signaling across GPR84-overexpressing cells, primary murine macrophages, and human U937 cells. By comparing DL-175 with reported GPR84 ligands, we show for the first time that biased GPR84 agonists have markedly different abilities to induce chemotaxis in human myeloid cells, while causing similar levels of phagocytosis enhancement. This work demonstrates that biased agonism at GPR84 enables the selective activation of functional responses in immune cells and delivers a high-quality chemical probe for further investigation.

Helicobacter pylori is a pathogen that chronically colonizes the stomachs of approximately half of the world's population and contributes to the development of gastric inflammation. We demonstrated previously in vivo that H. pylori uses motility to preferentially colonize injury sites in the mouse stomach. However, the chemoreceptor responsible for sensing gastric injury has not yet been identified. In this study, we utilized murine gastric organoids (gastroids) and mutant H. pylori strains to investigate the components necessary for H. pylori chemotaxis. High-intensity 730-nm light (two-photon photodamage) was used to cause single-cell damage in gastroids, and repair of the damage was monitored over time; complete repair occurred within ∼10 min in uninfected gastroids. Wild-type H. pylori accumulated at the damage site after gastric damage induction. In contrast, mutants lacking motility (Δ motB ) or chemotaxis (Δ cheY ) did not accumulate at the injury site. Using mutants lacking individual chemoreceptors, we found that only TlpB was required for H. pylori accumulation, while TlpA, TlpC, and TlpD were dispensable. All strains that were able to accumulate at the damage site limited repair. When urea (an identified chemoattractant sensed by TlpB) was microinjected into the gastroid lumen, it prevented the accumulation of H. pylori at damage sites. Overall, our findings demonstrate that H. pylori colonizes and limits repair at damage sites via chemotactic motility that requires the TlpB chemoreceptor to sense signals generated by gastric epithelial cells., (Copyright © 2019 American Society for Microbiology.)

Background: Entomological monitoring is important for public health because it provides data on the distribution, abundance and host-seeking behaviour of disease vectors. Various methods for sampling mosquitoes exist, most of which are biased towards, or specifically target, certain portions of a mosquito population. This study assessed the Suna trap, an odour-baited trap for sampling host-seeking mosquitoes both indoors and outdoors., Methods: Two separate field experiments were conducted in villages in southern Malawi. The efficiency of the Suna trap in sampling mosquitoes was compared to that of the human landing catch (HLC) indoors and outdoors and the Centers for Disease, Control and Prevention Light Trap (CDC-LT) indoors. Potential competition between two Suna traps during simultaneous use of the traps indoors and outdoors was assessed by comparing mosquito catch sizes across three treatments: one trap indoors only; one trap outdoors only; and one trap indoors and one trap outdoors used simultaneously at the same house., Results: The efficiency of the Suna trap in sampling female anophelines was similar to that of HLC indoors (P = 0.271) and HLC outdoors (P = 0.125), but lower than that of CDC-LT indoors (P = 0.001). Anopheline catch sizes in the Suna trap used alone indoors were similar to indoor Suna trap catch sizes when another Suna trap was simultaneously present outdoors (P = 0.891). Similarly, catch sizes of female anophelines with the Suna trap outdoors were similar to those that were caught outdoors when another Suna trap was simultaneously present indoors (P = 0.731)., Conclusions: The efficiency of the Suna trap in sampling mosquitoes was equivalent to that of the HLC. Whereas the CDC-LT was more efficient in collecting female anophelines indoors, the use of this trap outdoors is limited given the requirement of setting it next to an occupied bed net. As demonstrated in this research, outdoor collections are also essential because they provide data on the relative contribution of outdoor biting to malaria transmission. Therefore, the Suna trap could serve as an alternative to the HLC and the CDC-LT, because it does not require the use of humans as natural baits, allows standardised sampling conditions across sampling points, and can be used outdoors. Furthermore, using two Suna traps simultaneously indoors and outdoors does not interfere with the sampling efficiency of either trap, which would save a considerable amount of time, energy, and resources compared to setting the traps indoors and then outdoors in two consecutive nights.

The chemotactic activity of the pathogen of bacterial wilt disease, Ralstonia solanacearum, was tested against 30 aromatic acids and plant hormones infused on filter discs in bioassays on agar plates. 4-Hydroxycinnamic acid ( p-coumaric acid) and 4-hydroxybenzoic acid were strong chemoattractants, 3,4-dihydroxybenzoic acid (protocatechuic acid) and jasmonic acid were weak attractants, and 2-hydroxybenzoic acid (salicylic acid) showed both attracting and repelling activity depending on dose. Examination of the dose dependency revealed that the ED 50 for 4-hydroxycinnamic acid and 4-hydroxybenzoic acid was 0.08 and 0.39 μmol/disc, respectively. 2-Hydroxybenzoic acid showed chemoattractant activity at 0.33 μmol/disc but chemorepellent activity at 3.3 μmol/disc, and bacterial random motility was activated at 1.0 μmol/disc and bacterial activity was suppressed at 33 μmol/disc. Although water-soluble attractants including amino acids and organic acids have been previously investigated, this is the first report of hydroxylated aromatic acids (HAAs) as chemoattractants of R. solanacearum.

A chemoattractant of Ralstonia solanacearum isolated from the activated charcoal-adsorbed fraction of tomato root exudates was identified as ethyl β-d-glucopyranoside by instrumental analyses and comparison with synthetic preparations. Ethyl β-D-glucopyranoside showed unambiguous activity at above 1 µmol/disc. Its stereoisomers and D-glucose were inactive.

Arrestins are key adaptor proteins that control the fate of cell-surface membrane proteins and modulate downstream signaling cascades. The Dictyostelium discoideum genome encodes six arrestin-related proteins, harboring additional modules besides the arrestin domain. Here, we studied AdcB and AdcC, two homologs that contain C2 and SAM domains. We showed that AdcC - in contrast to AdcB - responds to various stimuli (such as the chemoattractants cAMP and folate) known to induce an increase in cytosolic calcium by transiently translocating to the plasma membrane, and that calcium is a direct regulator of AdcC localization. This response requires the calcium-dependent membrane-targeting C2 domain and the double SAM domain involved in AdcC oligomerization, revealing a mode of membrane targeting and regulation unique among members of the arrestin clan. AdcB shares several biochemical properties with AdcC, including in vitro binding to anionic lipids in a calcium-dependent manner and auto-assembly as large homo-oligomers. AdcB can interact with AdcC; however, its intracellular localization is insensitive to calcium. Therefore, despite their high degree of homology and common characteristics, AdcB and AdcC are likely to fulfill distinct functions in amoebae., Competing Interests: Competing interestsThe authors declare no competing or financial interests., (© 2018. Published by The Company of Biologists Ltd.)

Due to its chemoattraction potential on mesenchymal stromal cells of the CCL25/CCR9 axis, local application of CCL25 to severely damaged tissues may be a promising approach for regenerative therapies. Analysis of the given data revealed that CCL25/CCR9 signaling has a crucial role in regulation of an adult immune homeostasis. CCR9 expression variations resulted in dysfunctional immune response in colitis, rheumatoid arthritis and endometriosis. Regarding oncology, different neoplastic tissues exploit CCL25-dependent CCR9 signaling for either local proliferation or migration processes. The CCR9 pathway likely can trigger crosstalk between the Akt and NOTCH pathway and thus participate in the regulation of the neoplastic behavior. In conclusion, the designated application-tissue requires precise molecular analysis of possible CCR9 expression due to its proto-oncogenic characteristics.

To study the dynamics and mechanisms controlling activation of the heterotrimeric G protein Gα2βγ in Dictyostelium in response to stimulation by the chemoattractant cyclic AMP (cAMP), we monitored the G protein subunit interaction in live cells using bioluminescence resonance energy transfer (BRET). We found that cAMP induces the cAR1-mediated dissociation of the G protein subunits to a similar extent in both undifferentiated and differentiated cells, suggesting that only a small number of cAR1 (as expressed in undifferentiated cells) is necessary to induce the full activation of Gα2βγ. In addition, we found that treating cells with caffeine increases the potency of cAMP-induced Gα2βγ activation; and that disrupting the microtubule network but not F-actin inhibits the cAMP-induced dissociation of Gα2βγ. Thus, microtubules are necessary for efficient cAR1-mediated activation of the heterotrimeric G protein. Finally, kinetics analyses of Gα2βγ subunit dissociation induced by different cAMP concentrations indicate that there are two distinct rates at which the heterotrimeric G protein subunits dissociate when cells are stimulated with cAMP concentrations above 500 nM versus only one rate at lower cAMP concentrations. Quantitative modeling suggests that the kinetics profile of Gα2βγ subunit dissociation results from the presence of both uncoupled and G protein pre-coupled cAR1 that have differential affinities for cAMP and, consequently, induce G protein subunit dissociation through different rates. We suggest that these different signaling kinetic profiles may play an important role in initial chemoattractant gradient sensing., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Urocanic acid (UCA) is known as a major chemoattractant for Strongyloides stercoralis infective third-stage larvae (L3). Since Brugia pahangi is a skin-penetrating parasitic nematode similar to S. stercoralis, UCA was expected to be a chemoattractant for B. pahangi L3. Thus, the chemoattractant activity of UCA for B. pahangi L3 was assessed. The chemotactic responses of B. pahangi L3 to UCA or acetic acid (CH3COOH) dissolved in amine solutions were assessed using an agar-plate assay. A test solution of 200 mm UCA dissolved in aqueous 270 mm tris(hydroxymethyl)aminomethane (Tris) significantly attracted B. pahangi L3 compared with deionized water (DW), while neither a solution of 200 mm UCA dissolved in aqueous 230 mm ammonia (NH3) nor 290 mm triethylamine (TEA) significantly attracted L3. Similarly, a test solution of 200 mm CH3COOH dissolved with 200 mm Tris significantly attracted L3, but neither a test solution of 200 mm CH3COOH plus 200 mm NH3 nor 200 mm TEA attracted L3. Furthermore, L3 were significantly attracted to 200 mm Tris alone, compared with DW, but avoided 200 mm NH3 and 200 mm TEA. Moreover, the chemoattractant activity of Tris for L3 was observed even at a low concentration of 25 mm, and it was observed in a mild alkaline condition but not in an acidic condition. The present study reveals that Tris is a potential chemoattractant for B. pahangi L3 while UCA is not. This finding will contribute to an understanding of the mechanisms of skin-penetrating infection of filarial L3.

We previously identified the indole 264 as a potent in vitro antagonist of the human OXE receptor that mediates the actions of the powerful eosinophil chemoattractant 5-oxo-ETE. No antagonists of this receptor are currently commercially available or are being tested in clinical studies. The lack of a rodent ortholog of the OXE receptor has hampered progress in this area because of the unavailability of commonly used mouse or rat animal models. In the present study, we examined the feasibility of using the cynomolgus monkey as an animal model to investigate the efficacy of orally administered 264 in future in vivo studies. We first confirmed that 264 is active in monkeys by showing that it is a potent inhibitor of 5-oxo-ETE-induced actin polymerization and chemotaxis in granulocytes. The major microsomal metabolites of 264 were identified by cochromatography with authentic chemically synthesized standards and LC-MS/MS as its ω2-hydroxy and ω2-oxo derivatives, formed by ω2-oxidation of its hexyl side chain. Small amounts of ω1-oxidation products were also identified. None of these metabolites have substantial antagonist potency. High levels of 264 appeared rapidly in the blood following oral administration to both rats and monkeys, and declined to low levels by 24 h. As with microsomes, its major plasma metabolites in monkeys were ω2-oxidation products. We conclude that the monkey is a suitable animal model to investigate potential therapeutic effects of 264. This, or a related compound with diminished susceptibility to ω2-oxidation, could be a useful therapeutic agent in eosinophilic disorders such as asthma., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Chemotaxis is a ubiquitous biological phenomenon in which cells detect a spatial gradient of chemoattractant, and then move towards the source. Here we present a position-dependent advection-diffusion model that quantitatively describes the statistical features of the chemotactic motion of the social amoeba Dictyostelium discoideum in a linear gradient of cAMP (cyclic adenosine monophosphate). We fit the model to experimental trajectories that are recorded in a microfluidic setup with stationary cAMP gradients and extract the diffusion and drift coefficients in the gradient direction. Our analysis shows that for the majority of gradients, both coefficients decrease over time and become negative as the cells crawl up the gradient. The extracted model parameters also show that besides the expected drift in the direction of the chemoattractant gradient, we observe a nonlinear dependency of the corresponding variance on time, which can be explained by the model. Furthermore, the results of the model show that the non-linear term in the mean squared displacement of the cell trajectories can dominate the linear term on large time scales.

Bacteria are able to coordinate their movement, growth and biochemical activities through cell-cell communication. While the biophysical mechanism of bacterial chemotaxis has been well understood in individual cells, the role of communication in the chemotaxis of bacterial populations is not clear. Here we report experimental evidence for cell-cell communication that significantly enhances the chemotactic migration of bacterial populations, a finding that we further substantiate using numerical simulations. Using a microfluidic approach, we find that E. coli cells respond to the gradient of chemoattractant not only by biasing their own random-walk swimming pattern through the well-understood intracellular chemotaxis signaling, but also by actively secreting a chemical signal into the extracellular medium, possibly through a hitherto unknown communication signal transduction pathway. This extracellular signaling molecule is a strong chemoattractant that attracts distant cells to the food source. The observed behavior may represent a common evolved solution to accelerate the function of biochemical networks of interacting cells.

Background: The main goal of bone tissue engineering has been the generation of healthy bone in order to replace affected tissue. Therefore, optimized biomaterials are needed which allow the survival and growth of mesenchymal stem cells. Until now the key challenge in the clinical application of cell-based tissue engineering bone implants was poor diffusion of oxygen into the tissue, making functional blood vessel networks a necessity. With their ability to evolve into different cell types, to expand extensively in vitro, and to release paracrine soluble factors, bone marrow stromal cells (BMSC) are highly attractive for tissue engineering. During the last years hypoxia became a proven method to control proliferation, differentiation, and pluripotency of BMSC. Here we applied different methods to characterize metabolically conditioned media (MCM) in comparison to hypoxia conditioned media (HCM) and evaluated their ability to attract BMSC in 2-D migration assays., Methods: BMSC and fibroblasts of human origin were isolated and cultivated to obtain HCM and MCM. Both media were characterized by angiogenesis arrays, cytokine arrays, and ELISA for selected factors. 2-D migration tests were performed with Corning Transwell®-96 permeable support chambers with porous polyester membranes with a pore size of 8.0 μm., Results: Characterization of HCM and MCM revealed that the concentration of angiogenic factors was higher in MCM than in HCM. However, the chemoattractive capacity of MCM for BMSC was equivalent to that of HCM. HCM and MCM produced by human skin fibroblasts attracted human BMSC as efficiently as HCM and MCM produced by human BMSC., Conclusions: HCM and MCM have a high chemoattractive capacity for BMSC. Both conditioned media harbor high concentrations of angiogenic factors which are important for angiogenesis and cell migration. Both chemoattracting conditioned media can also be derived from skin fibroblasts which can easily be obtained from patients in individualized therapy approaches.

In bacteria various tactic responses are mediated by the same cellular pathway, but sensing of physical stimuli remains poorly understood. Here, we combine an in-vivo analysis of the pathway activity with a microfluidic taxis assay and mathematical modeling to investigate the thermotactic response of Escherichia coli . We show that in the absence of chemical attractants E. coli exhibits a steady thermophilic response, the magnitude of which decreases at higher temperatures. Adaptation of wild-type cells to high levels of chemoattractants sensed by only one of the major chemoreceptors leads to inversion of the thermotactic response at intermediate temperatures and bidirectional cell accumulation in a thermal gradient. A mathematical model can explain this behavior based on the saturation-dependent kinetics of adaptive receptor methylation. Lastly, we find that the preferred accumulation temperature corresponds to optimal growth in the presence of the chemoattractant serine, pointing to a physiological relevance of the observed thermotactic behavior.

Soybean cyst nematode (SCN) Heterodera glycines Ichinohe, a plant parasite, is one of the most serious pests of soybean. In this paper, we report that SCN is attracted to nitrate and its analogs. We performed attraction assays to screen for novel attractants for SCN and found that nitrates were attractants for SCN and SCN recognized nitrate gradients. However, attraction of SCN to nitrates was not observed on agar containing nitrate. To further elucidate the attraction mechanism in SCN, we performed attraction assays using nitrate analogs ([Formula: see text], [Formula: see text], [Formula: see text]). SCN was attracted to all nitrate analogs; however, attraction of SCN to nitrate analogs was not observed on agar containing nitrate. In contrast, SCN was attracted to azuki root, irrespective of presence or absence of nitrate in agar media. Our results suggest that the attraction mechanisms differ between plant-derived attractant and nitrate.

Efficient directed migration requires tight regulation of chemoattractant signal transduction pathways in both space and time, but the mechanisms involved in such regulation are not well understood. Here, we investigated the role of protein kinase A (PKA) in controlling signaling of the chemoattractant cAMP in Dictyostelium discoideum We found that cells lacking PKA display severe chemotaxis defects, including impaired directional sensing. Although PKA is an important regulator of developmental gene expression, including the cAMP receptor cAR1, our studies using exogenously expressed cAR1 in cells lacking PKA, cells lacking adenylyl cyclase A (ACA) and cells treated with the PKA-selective pharmacological inhibitor H89, suggest that PKA controls chemoattractant signal transduction, in part, through the regulation of RasG, Rap1 and TORC2. As these pathways control the ACA-mediated production of intracellular cAMP, they lie upstream of PKA in this chemoattractant signaling network. Consequently, we propose that the PKA-mediated regulation of the upstream RasG, Rap1 and TORC2 signaling pathways is part of a negative feedback mechanism controlling chemoattractant signal transduction during Dictyostelium chemotaxis., Competing Interests: Competing interestsThe authors declare no competing or financial interests., (© 2017. Published by The Company of Biologists Ltd.)

Activation of neutrophils is accompanied by the oxidative burst, exocytosis of various granule types (degranulation) and a delay in spontaneous apoptosis. The major source of reactive oxygen species (ROS) in human neutrophils is NADPH oxidase (NOX2), however, other sources of ROS also exist. Although the function of ROS is mainly defensive, they can also play a regulatory role in cell signaling. However, the contribution of various sources of ROS in these processes is not clear. We investigated a possible role of mitochondria-derived ROS (mtROS) in the regulation of neutrophil activation induced by chemoattractant fMLP in vitro. Using the mitochondria-targeted antioxidant SkQ1, we demonstrated that mtROS are implicated in the oxidative burst caused by NOX2 activation as well as in the exocytosis of primary (azurophil) and secondary (specific) granules. Scavenging of mtROS with SkQ1 slightly accelerated spontaneous apoptosis and significantly stimulated apoptosis of fMLP-activated neutrophils. These data indicate that mtROS play a critical role in signal transduction that mediates the major neutrophil functional responses in the process of activation., (Copyright © 2017 Elsevier GmbH. All rights reserved.)

The efficient recruitment of immune cells is a vital cornerstone of our defense against infections and a key challenge of immunotherapeutic applications. It relies on the ability of chemotaxing cells to prioritize their responses to different stimuli. For example, immune cells are known to abandon gradients of host-cell-produced cytokines in favor of complement-derived anaphylatoxins, which then guide the cells toward nearby pathogen surfaces. The aptitude to triage stimuli depends on the cells' specific sensitivities to different chemoattractants. We here use human neutrophils as uniquely capable biodetectors to map out the anaphylatoxic cloud that surrounds microbes in the presence of host serum. We quantify the neutrophil sensitivity in terms of the ratio between the chemoattractant concentration c and the production rate j 0 of the chemoattractant at the source surface. An integrative experimental/theoretical approach allows us to estimate the c/j 0 -threshold at which human neutrophils first detect nearby β-glucan surfaces as c/j 0 ≈ 0.0044 s/μm., (Copyright © 2017 Biophysical Society. Published by Elsevier Inc. All rights reserved.)

The niacin receptor HCA2 is implicated in controlling inflammatory host responses with yet poorly understood mechanistic basis. We previously reported that HCA2 in A431 epithelial cells transduced Gβγ-protein kinase C- and Gβγ-metalloproteinase/EGFR-dependent MAPK/ERK signaling cascades. Here, we investigated the role of HCA2 in macrophage-mediated inflammation and the underlying mechanisms. We found that proinflammatory stimulants LPS, IL-6 and IL-1β up-regulated the expression of HCA2 on macrophages. Niacin significantly inhibited macrophage chemotaxis in response to chemoattractants fMLF and CCL2 by disrupting polarized distribution of F-actin and Gβ protein. Niacin showed a selected additive effect on chemoattractant-induced activation of ERK1/2, JNK and PI3K pathways, but only the MEK inhibitor UO126 reduced niacin-mediated inhibition of macrophage chemotaxis, while activation of ERK1/2 by EGF alone did not inhibit fMLF-mediated migration of HEK293T cells co-expressing HCA2 and fMLF receptor FPR1. In addition, niacin induced heterologous desensitization and internalization of FPR1. Furthermore, niacin rescued mice from septic shock by diminishing inflammatory symptoms and the effect was abrogated in HCA2 -/- mice. These results suggest that Gβγ/PKC-dependent ERK1/2 activation and heterologous desensitization of chemoattractant receptors are involved in the inhibition of chemoattractant-induced migration of macrophages by niacin. Thus, HCA2 plays a critical role in host protection against pro-inflammatory insults., Competing Interests: The authors declare no competing financial interests.

Microglial motility is tightly controlled by multitude of agonistic and antagonistic factors. Chemoattractants, released after infection or damage of the brain, provoke directed migration of microglia to the pathogenic incident. In contrast, noradrenaline and other stress hormones have been shown to suppress microglial movement. Here we asked for the signaling reactions involved in the positive and negative control of microglial motility. Using pharmacological and genetic approaches we identified the lipid kinase activity of phosphoinositide 3-kinase species γ (PI3Kγ) as an essential mediator of microglial migration provoked by the complement component C5a and other chemoattractants. Inhibition of PI3Kγ lipid kinase activity by protein kinase A was disclosed as mechanism causing suppression of microglial migration by noradrenaline. Together these data characterize PI3Kγ as a nodal point in the control of microglial motility., (Copyright © 2016 Elsevier Inc. All rights reserved.)

Plants release volatiles in response to caterpillar feeding that attract natural enemies of the herbivores, a tri-trophic interaction which has been considered an indirect plant defence against herbivores. The caterpillar-induced plant volatiles have been reported to repel or attract conspecific adult herbivores. To date however, no volatile signals that either repel or attract conspecific adults under field conditions have been chemically identified. Apple seedlings uniquely released seven compounds including acetic acid, acetic anhydride, benzyl alcohol, benzyl nitrile, indole, 2-phenylethanol, and (E)-nerolidol only when infested by larvae of the light brown apple moth, Epiphyas postvittana. In field tests in New Zealand, a blend of two of these, benzyl nitrile and acetic acid, attracted a large number of conspecific male and female adult moths. In North America, male and female adults of the tortricid, oblique-banded leafroller, Choristoneura rosaceana, were most attracted to a blend of 2-phenylethanol and acetic acid. Both sexes of the eye-spotted bud moth, Spilonota ocellana, were highly attracted to a blend of benzyl nitrile and acetic acid. This study provides the first identification of caterpillar-induced plant volatiles that attract conspecific adult herbivores under natural conditions, challenging the expectation of herbivore avoidance of these induced volatiles.

Signal transduction pathways activated by chemoattractants have been extensively studied, but little is known about the events mediating responses to mechanical stimuli. We discovered that acute mechanical perturbation of cells triggered transient activation of all tested components of the chemotactic signal transduction network, as well as actin polymerization. Similarly to chemoattractants, the shear flow-induced signal transduction events displayed features of excitability, including the ability to mount a full response irrespective of the length of the stimulation and a refractory period that is shared with that generated by chemoattractants. Loss of G protein subunits, inhibition of multiple signal transduction events, or disruption of calcium signaling attenuated the response to acute mechanical stimulation. Unlike the response to chemoattractants, an intact actin cytoskeleton was essential for reacting to mechanical perturbation. These results taken together suggest that chemotactic and mechanical stimuli trigger activation of a common signal transduction network that integrates external cues to regulate cytoskeletal activity and drive cell migration., Competing Interests: The authors declare no conflict of interest.

Triple-negative (TN) breast cancers (ER - PR - HER2 - ) are highly metastatic and associated with poor prognosis. Within this subtype, invasive, stroma-rich tumours with infiltration of inflammatory cells are even more aggressive. The effect of myeloid cells on reactive stroma formation in TN breast cancer is largely unknown. Here, we show that primary human monocytes have a survival advantage, proliferate in vivo and develop into immunosuppressive myeloid cells expressing the myeloid-derived suppressor cell marker S100A9 only in a TN breast cancer environment. This results in activation of cancer-associated fibroblasts and expression of CXCL16, which we show to be a monocyte chemoattractant. We propose that this migratory feedback loop amplifies the formation of a reactive stroma, contributing to the aggressive phenotype of TN breast tumours. These insights could help select more suitable therapies targeting the stromal component of these tumours, and could aid prediction of drug resistance.

Antimicrobial surfaces with covalently attached biocidal functionalities only kill microbes that come into direct contact with the surfaces (contact-killing surfaces). Herein, the activity of contact-killing surfaces is shown to be enhanced by using gradients in the concentration of soluble chemoattractants (CAs) to attract bacteria to the surfaces. Two natural and nonbiocidal CAs (aspartate and glucose) were used to attract bacteria to model surfaces decorated with quaternary ammonium groups (known to kill bacteria that come into contact with them). These results demonstrate the killing of Escherichia coli and Salmonella typhimurium, two common pathogens, at levels 10- to 20-times greater than that of the native surfaces alone. This approach is general and provides new strategies for the design of active or dynamic contact-killing surfaces with enhanced antimicrobial activities., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The spermatozoa delivered to the female genital tract need to swim towards the oocyte through viscous secretions. Once close to the oocyte, the spermatozoa are guided by a gradient of progesterone (P4) and other unknown chemoattractants via a process known as chemotaxis. Using polyvinylpyrrolidone to establish the conditions of viscosity, we examined the response of mouse spermatozoa to P4 Herein, we show that in low-viscous media, P4 induces hyperactive-like motility whereby sperm show erratic trajectories and non-progressive movement. However, an opposite response is produced in viscous medium in that trajectories are linear and motility is more progressive and less erratic. Our observations provide a behavioural explanation for the chemotaxis of spermatozoa swimming under viscous conditions in a spatial gradient of the chemoattractant P4 They also highlight the importance of using viscous solutions to mimic in vivo conditions when analysing sperm behaviour in response to any stimulus., (© 2016 Society for Reproduction and Fertility.)

Many eukaryotic cells chemotax, sensing and following chemical gradients. However, experiments show that even under conditions when single cells cannot chemotax, small clusters may still follow a gradient. This behavior is observed in neural crest cells, in lymphocytes, and during border cell migration in Drosophila, but its origin remains puzzling. Here, we propose a new mechanism underlying this "collective guidance," and study a model based on this mechanism both analytically and computationally. Our approach posits that contact inhibition of locomotion, where cells polarize away from cell-cell contact, is regulated by the chemoattractant. Individual cells must measure the mean attractant value, but need not measure its gradient, to give rise to directional motility for a cell cluster. We present analytic formulas for how the cluster velocity and chemotactic index depend on the number and organization of cells in the cluster. The presence of strong orientation effects provides a simple test for our theory of collective guidance.

The contribution of human neutrophils to the protection against fungal infections by Aspergillus fumigatus is essential but not fully understood. Whereas healthy people can inhale spores of A. fumigatus without developing disease, neutropenic patients and those receiving immunosuppressive drugs have a higher incidence of invasive fungal infections. To study the role of neutrophils in protection against A. fumigatus infections, we developed an in vitro assay in which the interactions between human neutrophils and A. fumigatus were observed in real time, at single-cell resolution, in precisely controlled conditions. We measured the outcomes of neutrophil-fungus interactions and found that human neutrophils have a limited ability to migrate toward A. fumigatus and block the growth of A. fumigatus conidia (proportion with growth blocked, 69%). The blocking ability of human neutrophils increased to 85.1% when they were stimulated by uniform concentrations of fMLP and was enhanced further, to 99.4%, in the presence of chemoattractant gradients. Neutrophils from patients receiving immunosuppressive treatment after transplantation were less effective against the fungus than those from healthy donors, and broader heterogeneity exists between patients, compared with healthy individuals. Further studies using this microfluidic platform will help understand the relevance of innate immune deficiencies responsible for the higher risk of fungal infections in patients with immunosuppressive disease., (© The Author 2015. Published by Oxford University Press for the Infectious Diseases Society of America. All rights reserved. For permissions, e-mail journals.permissions@oup.com.)

Successful clinical outcomes from transplantation of hematopoietic stem cells (HSCs) depend upon efficient HSC homing to bone marrow (BM), subsequent engraftment, and, finally, BM repopulation. Homing of intravenously administered HSCs from peripheral blood (PB) through the circulation to the BM stem cell niches, which is the first critical step that precedes their engraftment, is enforced by chemotactic factors released in the BM microenvironment that chemoattract HSCs. These chemotactic factors include α-chemokine stromal-derived factor 1 (SDF-1), the bioactive phosphosphingolipids sphingosine-1-phosphate (S1P) and ceramid-1-phosphate (C1P), and the extracellular nucleotides ATP and UTP. Stem cells may also respond to a Ca(2+) or H(+) gradient by employing calcium- or proton-sensing receptors, respectively. In this review, we will present emerging strategies based on ex vivo manipulation of graft HSCs that are aimed at enhancing the responsiveness of HSCs to BM-secreted chemoattractants and/or promoting HSC adhesion and seeding efficiency in the BM microenvironment.

Ginsenosides produced by ginseng (Panax quinquefolius L.) are mildly fungitoxic saponins; however, exposure of the ginseng root pathogen Pythium irregulare Buisman to ginsenosides enhances its growth in a dose dependent manner, leading to speculation that ginsenosides may function as chemoattractants and/or growth regulators in the context of the ginseng - P. irregulare pathosystem. In the present work, it was demonstrated that the treatment of ginseng plants with a relatively high dose of ginsenosides by dipping their roots into a solution of ginsenosides prior to planting results in delayed infection by P. irregulare in pot experiments, as monitored by non-invasive chlorophyll fluorescence imaging. In an attempt to determine whether this observation results from a protective effect of the ginsenosides, or from a modification of P. irregulare growth habit in response to ginsenosides present in the soil, standard in vitro disk diffusion assays were conducted. Here, exposure of P. irregulare to crude ginsenosides or pure ginsenoside Rb1, resulted in delayed hyphal progression, while enhancing aerial hyphae build-up around ginsenoside-treated disks. By contrast, assays with pure ginsenoside F2 resulted in clear zones of inhibition around treated disks. While it remains unclear whether ginsenosides act as chemoattractants for P. irregulare in vivo, the results here suggest that these saponins serve to alter the growth habit of this organism, both in vivo and in vitro., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Dictyostelium discoideum has proven an excellent model for the study of eukaryotic chemotaxis. During growth in its native environment, Dictyostelium phagocytose bacteria and fungi for primary nutrient capture. Growing Dictyostelium can detect these nutrient sources through chemotaxis toward the metabolic by-product folate. Although Dictyostelium grow as individual cells, nutrient depletion induces a multicellular development program and a separate chemotactic response pathway. During development, Dictyostelium synthesize and secrete cAMP, which serves as a chemoattractant to mobilize and coordinate cells for multicellular formation and development. Separate classes of GPCRs and Gα proteins mediate chemotactic signaling to the chemically distinct ligands. We discuss common and separate component responses of Dictyostelium to folate and cAMP during growth and development, and the advantages and disadvantages for each. As examples, we present biochemical assays to characterize the chemoattractant-induced kinase activations of mTORC2 and the ERKs.

Sperm require a sense of direction to locate the egg for fertilization. They follow gradients of chemical and physical cues provided by the egg or the oviduct. However, the principles underlying three-dimensional (3D) navigation in chemical landscapes are unknown. Here using holographic microscopy and optochemical techniques, we track sea urchin sperm navigating in 3D chemoattractant gradients. Sperm sense gradients on two timescales, which produces two different steering responses. A periodic component, resulting from the helical swimming, gradually aligns the helix towards the gradient. When incremental path corrections fail and sperm get off course, a sharp turning manoeuvre puts sperm back on track. Turning results from an 'off' Ca(2+) response signifying a chemoattractant stimulation decrease and, thereby, a drop in cyclic GMP concentration and membrane voltage. These findings highlight the computational sophistication by which sperm sample gradients for deterministic klinotaxis. We provide a conceptual and technical framework for studying microswimmers in 3D chemical landscapes.