Diffusible Signal Molecules Research Articles

N-Acyl Homoserine Lactone-Mediated Quorum Sensing in Aeromonas veronii biovar sobria Strain 159: Identification of LuxRI Homologs.

16 Quorum sensing (QS) is a mechanism that plays important roles in gene expression in response to an 17 expanding bacterial population. In many Gram-negative bacteria, N-acyl homoserine lactone is mainly 18 secreted as the diffusible signalling molecules. This QS system has been shown to control diverse array 19 of virulence and secondary metabolism. Recently, whole genome sequencing of Aeromonas veronii 20 biovar sobria strain 159 was performed. Genome comparison with closely-related Aeromonas species 21 showed that A. veronii strain 159 shares a high degree of genome synteny with A. hydrophila ATCC 22 7966. A detailed genome analysis and gene annotation led us to the findings that A. veronii strain 159 23 harbors QS system which relies on its signal generator, AveI and the transcriptional regulator, AveR. 24 This Aeromonas strain was found to secrete N-butanoylacyl homoserine lactone (C4-HSL). Its LuxIR 25 homologs are similar to proteins of LuxIR famililies among Aeromonas species. This study aims to 26 gain further insights into AveIR system and to compare with AhyIR from A. hydrophila ATCC 7966 27 and AsaIR from A. salmonicida. 28 29 30 31

Systematic Design of a Quorum Sensing-Based Biosensor for Enhanced Detection of Metal Ion in Escherichia Coli.

With the recent industrial expansion, heavy metals and other pollutants have increasingly contaminated our living surroundings. The non-degradability of heavy metals may lead to accumulation in food chains and the resulting toxicity could cause damage in organisms. Hence, detection techniques have gradually received attention. In this study, a quorum sensing (QS)-based amplifier is introduced to improve the detection performance of metal ion biosensing. The design utilizes diffusible signal molecules, which freely pass through the cell membrane into the environment to communicate with others. Bacteria cooperate via the cell-cell communication process, thereby displaying synchronous behavior, even if only a minority of the cells detect the metal ion. In order to facilitate the design, the ability of the engineered biosensor to detect metal ion is described in a steady state model. The design can be constructed according to user-oriented specifications by selecting adequate components from corresponding libraries, with the help of a genetic algorithm (GA)-based design method. The experimental results validate enhanced efficiency and detection performance of the quorum sensing-based biosensor of metal ions.

Cpne7 is a signaling molecule from preameloblasts and regulates the differentiation of mesenchymal cells into odontoblasts

Event Abstract Back to Event Cpne7 is a signaling molecule from preameloblasts and regulates the differentiation of mesenchymal cells into odontoblasts Joo-Cheol Park1, Han-Wool Choung1 and Hyun-Sook Bae2 1 School of Dentistry, Seoul National University, Department of Oral Histology-Developmental Biology, Korea 2 Namseoul University, Department of Dental Hygiene, Korea Stem cell biology has emerged as one of the fundamental underpinnings for regenerative medicine. To achieve a clinical success with stem cell based therapy, it is important to understand the molecular and cellular basis of stem cells. Tooth development involves sequential interactions between dental epithelial and mesenchymal cells. Our previous studies demonstrated that preameloblast-conditioned medium (PA-CM) induces the odontogenic differentiation of human dental pulp cells (hDPCs) and promotes dentin formation. PA-CM can induce vascularized pulp regeneration of hDPSCs with physiological structures in an empty root canal space. The protein Cpne7 was identified in PA-CM by liquid chromatography-tandem mass spectrometry and suggested as a candidate signaling molecule regulating odontoblast differentiation. We investigated biological function and mechanisms of Cpne7 in regulation of odontoblast differentiation. Cpne7 was expressed in preameloblasts and secreted to the extracellular matrix during ameloblast differentiation. After secretion, Cpne7 protein was translocated to differentiating odontoblasts. In differentiating odontoblasts, Cpne7 overexpression or treatment with recombinant Cpne7 significantly promoted the expression of Dspp in vitro. In contrast, siRNA-mediated inactivation of Cpne7 suppressed Dspp expression. In in vivo transplantation experiments, Cpne7 induced odontoblast differentiation and promoted formation of dentin/pulp-like tissue in dental mesenchymal cells, such as hDPCs. Moreover, Cpne7 induced differentiation into odontoblasts of undifferentiated mesenchymal C3H10T1/2 cells in vitro and of non-dental mesenchymal cells, such as human bone marrow mesenchymal stem cells, with formation of dentin-like mineralized tissues including the structure of dentinal tubules in vivo. Mechanistically, Cpne7 interacted with Nucleolin and modulated odontoblast differentiation via the control of Dspp expression. These results suggest Cpne7 is a diffusible signaling molecule that is secreted by preameloblasts and regulates the differentiation of mesenchymal cells of dental or non-dental origin into odontoblasts. Therefore, regulation of Cpne7 expression in mesenchymal stem cells could be a novel therapeutic approach for the treatment of diseased dentin-pulp complex. Keywords: Cell Differentiation, stem cell, growth factor, Tissue Regeneration Conference: 10th World Biomaterials Congress, Montréal, Canada, 17 May - 22 May, 2016. Presentation Type: Poster Topic: Regenerative medicine: biomaterials for control of tissue induction Citation: Park J, Choung H and Bae H (2016). Cpne7 is a signaling molecule from preameloblasts and regulates the differentiation of mesenchymal cells into odontoblasts. Front. Bioeng. Biotechnol. Conference Abstract: 10th World Biomaterials Congress. doi: 10.3389/conf.FBIOE.2016.01.02430 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 27 Mar 2016; Published Online: 30 Mar 2016. Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Joo-Cheol Park Han-Wool Choung Hyun-Sook Bae Google Joo-Cheol Park Han-Wool Choung Hyun-Sook Bae Google Scholar Joo-Cheol Park Han-Wool Choung Hyun-Sook Bae PubMed Joo-Cheol Park Han-Wool Choung Hyun-Sook Bae Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Detection of Quorum Sensing Molecules and Biofilm Formation in Ralstonia solanacearum.

Many bacteria use small diffusible signaling molecules to communicate each other termed as quorum sensing (QS). Most Gram-negative bacteria use acyl homoserine lactone (AHL) as QS signal molecules. Using these signaling molecules, bacteria are able to express specific genes in response to population density. This work aimed to detect the production of QS signal molecules and biofilm formation in Ralstonia solanacearum isolated from various diseased tomato plants with symptoms of bacterial wilt. A total of 30 R. solanacearum strains were investigated for the production of QS signal molecules using Chromobacterium violaceum CV026 and Agrobacterium tumefaciens NT1 (pZLR4) biosensor systems. All 30 bacterial isolates from various bacterial wilt-affected tomato plants produced AHL molecules that induced the biosensor. The microtiter plate assay demonstrated that of the 30 bacterial isolates, 60 % formed biofilm, among which four isolates exhibited a higher degree of biofilm formation. The biofilm-inducing factor was purified from these four culture supernatants. The structure of the responsible molecule was solved using nuclear magnetic resonance and mass spectroscopy and was determined to be 2-hydroxy-4-((methylamino)(phenyl)methyl) cyclopentanone (HMCP), which was confirmed by chemical synthesis and NMR. The Confocal laser scanning microscopic analysis showed well-developed biofilm architecture of bacteria when treated with HMCP. The knowledge we obtained from this study will be useful for further researcher on the role of HMCP molecule in biofilm formation.

Adsorption of N-acyl-Homoserine Lactone onto Colloidal Minerals Presents Potential Challenges for Quorum Sensing in the Soil Environment

Bacterial interspecies and intraspecies communications are mediated by diffusible signaling molecules. In complex natural environments, the fluctuation of geochemical and physical conditions presents substantial challenges to the environmental fate of N-acyl-homoserine lactones. Although researchers have attempted to elucidate the influence of aquatic environmental parameters on bacterial QS signals, insufficient information is known regarding their interactions with soil. Thus, the adsorption of N-(3-oxododecanoyl) homoserine lactone on three common soil minerals (montmorillonite, kaolinite, and goethite) was investigated by performing batch studies coupled with Fourier-transform infrared spectroscopy and isothermal titration calorimetry. The adsorption isotherms of N-(3-oxododecanoyl) homoserine lactone on these minerals conformed to the Langmuir equation; the adsorbed N-(3-oxododecanoyl) homoserine lactone amount increased significantly as electrolyte concentration increased from 0.001 mol L−1 to 0.1 mol L−1. The adsorption of N-(3-oxododecanoyl) homoserine lactone on goethite was enhanced with increasing pH values; by contrast that on montmorillonite and kaolinite showed less dependence in the 6.0–8.0 pH range. Hydrogen bonding and hydrophobic interaction had important functions in these processes. This study provided insights into the distribution and diffusion of N-acyl-homoserine lactone in soil and associated environments.

The DSF Family of Cell-Cell Signals: An Expanding Class of Bacterial Virulence Regulators.

Many pathogenic bacteria use cell–cell signaling systems involving the synthesis and perception of diffusible signal molecules to control virulence as a response to cell density or confinement to niches. Bacteria produce signals of diverse structural classes. Signal molecules of the diffusible signal factor (DSF) family are cis-2-unsaturated fatty acids. The paradigm is cis-11-methyl-2-dodecenoic acid from Xanthomonas campestris pv. campestris (Xcc), which controls virulence in this plant pathogen. Although DSF synthesis was thought to be restricted to the xanthomonads, it is now known that structurally related molecules are produced by the unrelated bacteria Burkholderia cenocepacia and Pseudomonas aeruginosa. Furthermore, signaling involving these DSF family members contributes to bacterial virulence, formation of biofilms and antibiotic tolerance in these important human pathogens. Here we review the recent advances in understanding DSF signaling and its regulatory role in different bacteria. These advances include the description of the pathway/mechanism of DSF biosynthesis, identification of novel DSF synthases and new members of the DSF family, the demonstration of a diversity of DSF sensors to include proteins with a Per-Arnt-Sim (PAS) domain and the description of some of the signal transduction mechanisms that impinge on virulence factor expression. In addition, we address the role of DSF family signals in interspecies signaling that modulates the behavior of other microorganisms. Finally, we consider a number of recently reported approaches for the control of bacterial virulence through the modulation of DSF signaling.

Coordinated Spatial Pattern Formation in Biomolecular Communication Networks

This paper proposes a control theoretic framework to model and analyze the self-organized pattern formation of molecular concentrations in biomolecular communication networks, emerging applications in synthetic biology. In biomolecular communication networks, bionanomachines, or biological cells, communicate with each other using a cell-to-cell communication mechanism mediated by a diffusible signaling molecule, thereby the dynamics of molecular concentrations are approximately modeled as a reaction-diffusion system with a single diffuser. We first introduce a feedback model representation of the reaction-diffusion system and provide a systematic local stability/instability analysis tool using the root locus of the feedback system. The instability analysis then allows us to analytically derive the conditions for the self-organized spatial pattern formation, or Turing pattern formation, of the bionanomachines. We propose a novel synthetic biocircuit motif called activator-repressor-diffuser system and show that it is one of the minimum biomolecular circuits that admit self-organized patterns over cell population.

Coupling intercellular molecular signalling with multicellular deformation for simulating three-dimensional tissue morphogenesis.

During morphogenesis, three-dimensional (3D) multicellular structures emerge from biochemical and mechanical interplays among cells. In particular, by organizing their gradient within tissues, the diffusible signalling molecules play an essential role in producing the spatio-temporal patterns of cell status such as the differentiation states. Notably, this biochemical patterning can be dynamically coupled with multicellular deformations by signal-dependent cell activities such as contraction, adhesion, migration, proliferation and apoptosis. However, the mechanism by which these cellular activities mediate the interactions between multicellular deformations and patterning is still unknown. Herein, we propose a novel framework of a 3D vertex model to express molecular signalling among the mechanically deforming cells. By specifying a density of signalling molecules for each cell, we express their transport between neighbouring cells. By simulating signal-dependent epithelial growth, we found various types of tissue morphogenesis such as arrest, expansion, invagination and evagination. In the expansion phase, growth molecules were widely diffused with increasing tissue volume, which diluted the growth molecules in order to support the autonomous suppression of tissue growth. These results indicate that the proposed model successfully expresses 3D multicellular deformations dynamically coupled with biochemical patterning. We expect our proposed model to be a useful tool for predicting new phenomena emerging from mechanochemical coupling in multicellular morphogenesis.

Microbial biofilm as a smart material.

Microbial biofilm colonies will in many cases form a smart material capable of responding to external threats dependent on their size and internal state. The microbial community accordingly switches between passive, protective, or attack modes of action. In order to decide which strategy to employ, it is essential for the biofilm community to be able to sense its own size. The sensor designed to perform this task is termed a quorum sensor, since it only permits collective behaviour once a sufficiently large assembly of microbes have been established. The generic quorum sensor construct involves two genes, one coding for the production of a diffusible signal molecule and one coding for a regulator protein dedicated to sensing the signal molecules. A positive feedback in the signal molecule production sets a well-defined condition for switching into the collective mode. The activation of the regulator involves a slow dimerization, which allows low-pass filtering of the activation of the collective mode. Here, we review and combine the model components that form the basic quorum sensor in a number of Gram-negative bacteria, e.g., Pseudomonas aeruginosa.

Non-social adaptation defers a tragedy of the commons in Pseudomonas aeruginosa quorum sensing.

In a process termed quorum sensing (QS), the opportunistic bacterial pathogen Pseudomonas aeruginosa uses diffusible signaling molecules to regulate the expression of numerous secreted factors or public goods that are shared within the population. But not all cells respond to QS signals. These social cheaters typically harbor a mutation in the QS receptor gene lasR and exploit the public goods produced by cooperators. Here we show that non-social adaptation under growth conditions that require QS-dependent public goods increases tolerance to cheating and defers a tragedy of the commons. The underlying mutation is in the transcriptional repressor gene psdR. This mutation has no effect on public goods expression but instead increases individual fitness by derepressing growth-limiting intracellular metabolism. Even though psdR mutant populations remain susceptible to invasion by isogenic psdR lasR cheaters, they bear a lower cheater load than do wild-type populations, and they are completely resistant to invasion by lasR cheaters with functional psdR. Mutations in psdR also sustain growth near wild-type levels when paired with certain partial loss-of-function lasR mutations. Targeted sequencing of multiple evolved isolates revealed that mutations in psdR arise before mutations in lasR, and rapidly sweep through the population. Our results indicate that a QS-favoring environment can lead to adaptations in non-social, intracellular traits that increase the fitness of cooperating individuals and thereby contribute to population-wide maintenance of QS and associated cooperative behaviors.

Quorum Sensing: a Novel Threat to Sociomicrobiology

Research in the field of science and technology has shown that bacteria can communicate with each other. This communication is population-density dependent and involves signalling molecules that can diffuse between the bacterial cells. The process of communication is called ‘quorum sensing’. Different species of bacteria are important in the composition of dental plaque. Many Gram-positive and Gram-negative bacteria communicate using small diffusible signal molecules called auto inducers. The interference with these signalling systems, also known as Quorum Quenching, represents a promising strategy to tackle bacterial infections.

Sodium houttuyfonate affects production of N-acyl homoserine lactone and quorum sensing-regulated genes expression in Pseudomonas aeruginosa.

Quorum sensing (QS) is a means of cell-to-cell communication that uses diffusible signaling molecules that are sensed by the population to determine population density, thus allowing co-ordinate gene regulation in response to population density. In Pseudomonas aeruginosa, production of the QS signaling molecule, N-acyl homoserine lactone (AHL), co-ordinates expression of key factors of pathogenesis, including biofilm formation and toxin secretion. It is predicted that the inhibition of AHL sensing would provide an effective clinical treatment to reduce the expression of virulence factors and increase the effectiveness of antimicrobial agents. We previously demonstrated that sodium houttuyfonate (SH), commonly used in traditional Chinese medicine to treat infectious diseases, can effectively inhibit QS-regulated processes, including biofilm formation. Here, using a model system, we demonstrate that SH causes the dose-dependent inhibition of AHL production, through down-regulation of the AHL biosynthesis gene, lasI. Addition of SH also resulted in down-regulation of expression of the AHL sensor and transcriptional regulator, LasR, and inhibited the production of the QS-regulated virulence factors, pyocyanin and LasA. These results suggest that the antimicrobial activity of SH may be due to its ability to disrupt QS in P. aeruginosa.

Strategies for antimicrobial drug delivery to biofilm.

Biofilms are formed by the attachment of single or mixed microbial communities to a variety of biological and/or synthetic surfaces. Biofilm micro-organisms benefit from many advantages of the polymicrobial environment including increased resistance against antimicrobials and protection against the host organism's defence mechanisms. These benefits stem from a number of structural and physiological differences between planktonic and biofilm-resident microbes, but two main factors are the presence of extracellular polymeric substances (EPS) and quorum sensing communication. Once formed, biofilms begin to synthesise EPS, a complex viscous matrix composed of a variety of macromolecules including proteins, lipids and polysaccharides. In terms of drug delivery strategies, it is the EPS that presents the greatest barrier to diffusion for drug delivery systems and free antimicrobial agents alike. In addition to EPS synthesis, biofilm-based micro-organisms can also produce small, diffusible signalling molecules involved in cell density-dependent intercellular communication, or quorum sensing. Not only does quorum sensing allow microbes to detect critical cell density numbers, but it also permits co-ordinated behaviour within the biofilm, such as iron chelation and defensive antibiotic activities. Against this backdrop of microbial defence and cell density-specific communication, a variety of drug delivery systems have been developed to deliver antimicrobial agents and antibiotics to extracellular and/or intracellular targets, or more recently, to interfere with the specific mechanisms of quorum sensing. Successful delivery strategies have employed lipidic and polymeric-based formulations such as liposomes and cyclodextrins respectively, in addition to inorganic carriers e.g. metal nanoparticles. This review will examine a range of drug delivery systems and their application to biofilm delivery, as well as pharmaceutical formulations with innate antimicrobial properties such as silver nanoparticles and microemulsions.

CPNE7, a preameloblast-derived factor, regulates odontoblastic differentiation of mesenchymal stem cells

Tooth development involves sequential interactions between dental epithelial and mesenchymal cells. Our previous studies demonstrated that preameloblast-conditioned medium (PA-CM) induces the odontogenic differentiation of human dental pulp cells (hDPCs), and the novel protein Cpne7 in PA-CM was suggested as a candidate signaling molecule. In the present study, we investigated biological function and mechanisms of Cpne7 in regulation of odontoblast differentiation. Cpne7 was expressed in preameloblasts and secreted extracellularly during ameloblast differentiation. After secretion, Cpne7 protein was translocated to differentiating odontoblasts. In odontoblasts, Cpne7 promoted odontoblastic markers and the expression of Dspp in vitro. Cpne7 also induced odontoblast differentiation and promoted dentin/pulp-like tissue formation in hDPCs in vivo. Moreover, Cpne7 induced differentiation into odontoblasts of non-dental mesenchymal stem cells in vitro, and promoted formation of dentin-like tissues including the structure of dentinal tubules in vivo. Mechanistically, Cpne7 interacted with Nucleolin and modulated odontoblast differentiation via the control of Dspp expression. These results suggest Cpne7 is a diffusible signaling molecule that is secreted by preameloblasts, and regulates the differentiation of mesenchymal cells of dental or non-dental origin into odontoblasts.

Traveling waves in response to a diffusing quorum sensing signal in spatially-extended bacterial colonies

In the behavior known as quorum sensing (QS), bacteria release diffusible signal molecules known as autoinducers, which by accumulating in the environment induce population-wide changes in gene expression. Although QS has been extensively studied in well-mixed systems, the ability of diffusing QS signals to synchronize gene expression in spatially extended colonies is not well understood. Here we investigate the one-dimensional spatial propagation of QS-circuit activation in a simple, analytically tractable reaction-diffusion model for the LuxR–LuxI circuit, which regulates bioluminescence of the marine bacterium Aliivibrio fischeri. The quorum activation loop is modeled by a Hill function with a cooperativity exponent (m=2.2). The model is parameterized from laboratory data and captures the major empirical properties of the LuxR–LuxI system and its QS regulation of A. fischeri bioluminescence. Our simulations of the model show propagating waves of activation or deactivation of the QS circuit in a spatially extended colony. We further prove analytically that the model equations possess a traveling wave solution. This mathematical proof yields the rate of autoinducer degradation that is compatible with a traveling wave of gene expression as well as the critical degradation rate at which the nature of the wave switches from activation to deactivation. Our results can be used to predict the direction and activating or deactivating nature of a wave of gene expression in experimentally controlled bacterial populations subject to a diffusing autoinducer signal.

RsaM: a transcriptional regulator of Burkholderia spp. with novel fold.

The atomic coordinates and structure factors have been deposited in the Protein Data Bank under entry 4O2H. BcRsaM and BcRsaM bind by x-ray crystallography (View interaction) BcRsaM and BcRsaM bind by molecular sieving (View interaction).

S7-6 Role of H2S and NO in Bacillus anthracis spore formation and virulence

Many prokaryotic species generate hydrogen sulfide (H2S) and nitric oxide (NO) enzymatically, from cysteine and arginine, respectively, in their natural environments. Both gases are small freely diffusible signaling molecules that are known to be involved in numerous physiological and pathological processes in mammals. However the biochemistry and physiological role of these gases in bacteria remains largely unknown. We have shown that inactivation of H2S producing enzymes (cystathionine beta-synthase, cystathionine gamma lyase, or 3-mercaptopyruvate sulfurtransferase) and NO-synthase in several Gram (+) and Gram (−) bacteria render them highly sensitive to different classes of antibiotics (Gusarov et al., Science 325 (2009) 1380–1384; Shatalin et al. Science 334 (2011) 986–990). We also presented evidence that Bacillus anthracis-derived NO is critical at the early stage of infection (Shatalin et al. PNAS 105 (2008) 1009–1013). Here we show that: (1) cbs/cse and nos mutations change Bacilli global gene transcription profile; (2) apore formation process in cbs/cse and nos mutants ofB. anthracis is affected; (3) virulence of cbs/cse and nos mutants of B. anthracis is diminished. These results demonstrate that bacterial H2S and NO are an important virulence factors, and that enzymes generated these gases may serve as an attractive target for antimicrobial therapy.

Reversible non‐genetic phenotypic heterogeneity in bacterial quorum sensing

Bacteria co-ordinate their social behaviour in a density-dependent manner by production of diffusible signal molecules by a process known as quorum sensing (QS). It is generally assumed that in homogenous environments and at high cell density, QS synchronizes cells in the population to perform collective social tasks in unison which maximize the benefit at the inclusive fitness of individuals. However, evolutionary theory predicts that maintaining phenotypic heterogeneity in performing social tasks is advantageous as it can serve as a bet-hedging survival strategy. Using Pseudomonas syringae and Xanthomonas campestris as model organisms, which use two diverse classes of QS signals, we show that two distinct subpopulations of QS-responsive and non-responsive cells exist in the QS-activated population. Addition of excess exogenous QS signal does not significantly alter the distribution of QS-responsive and non-responsive cells in the population. We further show that progeny of cells derived from these subpopulations also exhibited heterogeneous distribution patterns similar to their respective parental strains. Overall, these results support the model that bacteria maintain QS-responsive and non-responsive subpopulations at high cell densities in a bet-hedging strategy to simultaneously perform functions that are both positively and negatively regulated by QS to improve their fitness in fluctuating environments.

Diffusible signals and epigenetic timing cooperate in late proximo-distal limb patterning

Developing vertebrate limbs initiate proximo-distal patterning by interpreting opposing gradients of diffusible signaling molecules. We report two thresholds of proximo-distal signals in the limb bud: a higher threshold that establishes the upper-arm to forearm transition; and a lower one that positions a later transition from forearm to hand. For this last transition to happen, however, the signal environment seems to be insufficient, and we show that a timing mechanism dependent on histone acetylation status is also necessary. Therefore, as a consequence of the time dependence, the lower signaling threshold remains cryptic until the timing mechanism reveals it. We propose that this timing mechanism prevents the distal transition from happening too early, so that the prospective forearm has enough time to expand and form a properly sized segment. Importantly, the gene expression changes provoked by the first transition further regulate proximo-distal signal distribution, thereby coordinating the positioning of the two thresholds, which ensures robustness. This model is compatible with the most recent genetic analyses and underscores the importance of growth during the time-dependent patterning phase, providing a new mechanistic framework for understanding congenital limb defects.

Immune effects of high dose radiation treatment: implications of ionizing radiation on the development of bystander and abscopal effects

Tumors grow progressively when they escape from immune surveillance. Cancer progression is mainly driven by the expansion of tumor cells, but tumor microenvironment and anti-tumor immunity may also play a role. Ionizing radiation therapy (RT), either alone or in combination with additional immune stimulators, can render cancer cells visible to the immune system. In addition to the direct effects of radiation, the ensuing immune response promotes the expression of inflammatory and immunostimulatory mediators, which act on neighboring, non-irradiated, cells. Bystander effects induced by radiation are characterized by biological responses, which are observed in non-irradiated cells that are in the vicinity of irradiated cells. Bystander effects are mediated via cell-to-cell gap junctions or through secreted, diffusible signaling molecules into the local milieu. After treatment with localized radiation, systemic effects in non-irradiated area (out-offield) may also occur. These effects are named abscopal effects and appear to be immune mediated, particularly by adaptive immunity. It has been suggested that a high single dose of RT may induce an immune response that leads to the priming of antigen-specific dendritic cells (DCs). The targeted intraoperative radiotherapy (TARGIT) method, using INTRABEAM ® , could reduce tumor recurrence, modifying the wound microenvironment, and eradicating residual tumor cells when applied immediately after surgery procedure.