Cross-species Interactions Research Articles

Cross-Species Interaction between Rapidly Evolving Telomere-Specific Drosophila Proteins.

Telomere integrity in Drosophila melanogaster is maintained by a putative multisubunit complex called terminin that is believed to act in analogy to the mammalian shelterin complex in protecting chromosome ends from being recognized as sites of DNA damage. The five proteins supposed to form the terminin complex are HP1-ORC associated protein, HP1-HOAP interacting protein, Verrocchio, Drosophila Telomere Loss/Modigliani and Heterochromatic Protein 1. Four of these proteins evolve rapidly within the Drosophila genus. The accelerated evolution of terminin components may indicate the involvement of these proteins in the process by which new species arise, as the resulting divergence of terminin proteins might prevent hybrid formation, thus driving speciation. However, terminin is not an experimentally proven entity, and no biochemical studies have been performed to investigate its assembly and action in detail. Motivated by these facts in order to initiate biochemical studies on terminin function, we attempted to reconstitute terminin by co-expressing its subunits in bacteria and investigated the possible role of the fast-evolving parts of terminin components in complex assembly. Our results suggest formation of stable subcomplexes of terminin, but not of the whole complex in vitro. We found that the accelerated evolution is restricted to definable regions of terminin components, and that the divergence of D. melanogaster Drosophila Telomere Loss and D. yakuba Verrocchio proteins does not preclude their stable interaction.

Coevolutionary analyses require phylogenetically deep alignments and better null models to accurately detect inter-protein contacts within and between species.

BackgroundWhen biomolecules physically interact, natural selection operates on them jointly. Contacting positions in protein and RNA structures exhibit correlated patterns of sequence evolution due to constraints imposed by the interaction, and molecular arms races can develop between interacting proteins in pathogens and their hosts. To evaluate how well methods developed to detect coevolving residues within proteins can be adapted for cross-species, inter-protein analysis, we used statistical criteria to quantify the performance of these methods in detecting inter-protein residues within 8 angstroms of each other in the co-crystal structures of 33 bacterial protein interactions. We also evaluated their performance for detecting known residues at the interface of a host-virus protein complex with a partially solved structure.ResultsOur quantitative benchmarking showed that all coevolutionary methods clearly benefit from alignments with many sequences. Methods that aim to detect direct correlations generally outperform other approaches. However, faster mutual information based methods are occasionally competitive in small alignments and with relaxed false positive rates. Two commonly used null distributions are anti-conservative and have high false positive rates in some scenarios, although the empirical distribution of scores performs reasonably well with deep alignments.ConclusionsWe conclude that coevolutionary analysis of cross-species protein interactions holds great promise but requires sequencing many more species pairs.Electronic supplementary materialThe online version of this article (doi:10.1186/s12859-015-0677-y) contains supplementary material, which is available to authorized users.

Etiological Structure and Features of a Symbiotic Relationship Dominates Agents Acute Intestinal Infections in the North-Eastern Regione of Ukraine

The article shows a retrospective epidemiological analysis of the incidence of acute intestinal diseases in 2004 – 2013 in Sumy region. The etiological structure was studied. The properties of Klebsiella pneumoniaе, Enterobacter cloacae, Staphylococcus aureus and Salmonella Enteritidis in a cross-species interaction in populations were studied. It was found, the incidence rates were in the range 159.8 – 193.9 per 100 000 population. The structure of the nosology of acute infectious diarrhea, acute intestinal infection caused by opportunistic pathogens accounted 44.4%. Among the etiologic agents prevailed Klebsiella (28.2 – 34.7%), S. aureus (17.1 – 25.2%) and Enterobacter (12.6 – 18.8%) (p < 0.05). From fecal samples of children were isolated Rotaviruses in 39.5% of cases, adenoviruses – 28.2%, noro-, enteric- and astroviruses respectively – 26.2, 10.4 and 3.2%. It was found the changes in microecological characteristics of intestinal biocenosis in individuals without signs of acute intestinal infection. Association of micro-organisms was characterized by the absence or reduction in the number of representatives of obligate (Bifidobacterium), increasing the number of Enterobacteriaceae, the presence of coliform hemolysing, fungi of the genus Candida, coagulase-negative staphylococci. Among causative agents of diarrhoeal infections K. pneumoniae, E. cloacae and S. Еnteritidis in vitro were revealed indifferent relationships, S. aureus and S. Еnteritidis – synergistic.

Социально-психологические аспекты межвидового взаимодействия человека и домашних животных

Социально-психологические аспекты межвидового взаимодействия человека и домашних животных

Human–animal relationships in zoo‐housed orangutans (P. abelii) and gorillas (G. g. gorilla): The effects of familiarity

I examined human-animal relationships (HARs) in zoo-housed orangutans (Pongo abelii) and gorillas (Gorilla gorilla gorilla) to see if they followed patterns similar to conspecific relationships in great apes and humans. Familiarity and social relationships guide humans' and great apes' behaviors with conspecifics. Inter-individual relationships, based on shared social history, and "generalized" relationships, based on a history of interactions with relevant classes of individuals, guide behavior with familiar and unfamiliar conspecifics, respectively. I examined whether both familiarity and social relationships similarly guides great apes' cross-species interactions with humans. I used repeated measures MANOVA to compare hourly rates and average durations of ape-initiated human-directed behaviors (HDBs) between familiar and unfamiliar humans and between great ape species. HDB patterns were consistent with familiarity-based HAR predictions, indicating more negative relationships with unfamiliar humans and more positive relationships with familiar humans. Findings for unfamiliar humans are consistent with negative effects of humans on apes' behavior reported in traditional visitor effect studies (VES). However, findings for familiar humans may be overlooked in VES due to pooling across levels of human familiarity or failure to consider humans other than primarily unfamiliar visitors. Additionally, species differences in apes' HDBs suggest that data pooling across species, common in many zoo studies, may mask important differences. These findings have important methodological implications for studies of human-animal interaction as well as for captive animal wellbeing.

Lack of population genetic structure and host specificity in the bat fly, Cyclopodia horsfieldi, across species of Pteropus bats in Southeast Asia

BackgroundPopulation-level studies of parasites have the potential to elucidate patterns of host movement and cross-species interactions that are not evident from host genealogy alone. Bat flies are obligate and generally host-specific blood-feeding parasites of bats. Old-World flies in the family Nycteribiidae are entirely wingless and depend on their hosts for long-distance dispersal; their population genetics has been unstudied to date.MethodsWe collected a total of 125 bat flies from three Pteropus species (Pteropus vampyrus, P. hypomelanus, and P. lylei) from eight localities in Malaysia, Cambodia, and Vietnam. We identified specimens morphologically and then sequenced three mitochondrial DNA gene fragments (CoI, CoII, cytB; 1744 basepairs total) from a subset of 45 bat flies. We measured genetic diversity, molecular variance, and population genetic subdivision (FST), and used phylogenetic and haplotype network analyses to quantify parasite genetic structure across host species and localities.ResultsAll flies were identified as Cyclopodia horsfieldi with the exception of two individuals of Eucampsipoda sundaica. Low levels of population genetic structure were detected between populations of Cyclopodia horsfieldi from across a wide geographic range (~1000 km), and tests for isolation by distance were rejected. AMOVA results support a lack of geographic and host-specific population structure, with molecular variance primarily partitioned within populations. Pairwise FST values from flies collected from island populations of Pteropus hypomelanus in East and West Peninsular Malaysia supported predictions based on previous studies of host genetic structure.ConclusionsThe lack of population genetic structure and morphological variation observed in Cyclopodia horsfieldi is most likely due to frequent contact between flying fox species and subsequent high levels of parasite gene flow. Specifically, we suggest that Pteropus vampyrus may facilitate movement of bat flies between the three Pteropus species in the region. We demonstrate the utility of parasite genetics as an additional layer of information to measure host movement and interspecific host contact. These approaches may have wide implications for understanding zoonotic, epizootic, and enzootic disease dynamics. Bat flies may play a role as vectors of disease in bats, and their competence as vectors of bacterial and/or viral pathogens is in need of further investigation.

In vivo, in vitro, and in silico studies suggest a conserved immune module that regulates malaria parasite transmission from mammals to mosquitoes

Human malaria can be caused by the parasite Plasmodium falciparum that is transmitted by female Anopheles mosquitoes. “Immunological crosstalk” between the mammalian and anopheline hosts for Plasmodium functions to control parasite numbers. Key to this process is the mammalian cytokine transforming growth factor-β1 (TGF-β1). In mammals, TGF-β1 regulates inducible nitric oxide (NO) synthase (iNOS) both positively and negatively. In some settings, high levels of NO activate latent TGF-β1, which in turn suppresses iNOS expression. In the mosquito, ingested TGF-β1 induces A. stephensi NOS (AsNOS), which limits parasite development and which in turn is suppressed by activation of the mosquito homolog of the mitogen-activated protein kinases MEK and ERK. Computational models linking TGF-β1, AsNOS, and MEK/ERK were developed to provide insights into this complex biology. An initial Boolean model suggested that, as occurs in mammalian cells, MEK/ERK and AsNOS would oscillate upon ingestion of TGF-β1. An ordinary differential equation (ODE) model further supported the hypothesis of TGF-β1-induced multiphasic behavior of MEK/ERK and AsNOS. To achieve this multiphasic behavior, the ODE model was predicated on the presence of constant levels of TGF-β1 in the mosquito midgut. Ingested TGF-β1, however, did not exhibit this behavior. Accordingly, we hypothesized and experimentally verified that ingested TGF-β1 induces the expression of the endogenous mosquito TGF-β superfamily ligand As60A. Computational simulation of these complex, cross-species interactions suggested that TGF-β1 and NO-mediated induction of As60A expression together may act to maintain multiphasic AsNOS expression via MEK/ERK-dependent signaling.We hypothesize that multiphasic behavior as represented in this model allows the mosquito to balance the conflicting demands of parasite killing and metabolic homeostasis in the face of damaging inflammation.

Cross-species synthetic lethal interaction screening as a strategy for the identification of novel therapeutic targets in cancer.

11105 Background: Mutation, deletion, or epigenetic silencing of tumor suppressor genes is a near universal feature of malignant cells. However, therapeutic strategies for restoring the function of mutated or deleted genes have proven difficult. Synthetic lethality, an event in which the simultaneous perturbation of two genes results in cellular death, has been proposed as a method to selectively target cancer cells. Identifying and pharmacologically inhibiting proteins encoded by genes that are synthetic lethal with known tumor suppressor mutations should result in selective toxicity to tumor cells. Methods: To identify candidate target proteins we measured all pair-wise genetic interactions between all known orthologs of human tumor suppressor genes (162 genes) and all orthologs of druggable human proteins (~400 genes) in the model organism S. Cerevisiae. Analysis of the data uncovered 2,087 distinct synthetic lethal interactions between a tumor suppressor and druggable gene. A computational algorithm was then developed to identify those interactions which were likely to be conserved in humans based on conservation of the synthetic lethal relationship in the distant fission yeast S. pombe. Results: Our bioinformatic analysis suggested a high probability of conservation of the synthetic lethal interactions between the yeast RAD51 (ortholog of BRCA1) and RAD57 (ortholog of XRCC3) with HDA1 (a histone deacetylase; HDAC). We confirmed this by treating LN428 cells with stable lentiviral knockdown of BRCA1 or XRCC3 with the HDAC inhibitors vorinostat (SAHA) and entinostat (MS-275). Both the BRCA1 and XRCC3 knockdown cell lines were significantly more sensitive to HDAC inhibition relative to wild-type (non-silencing lentiviral control) cell line (Table). Conclusions: These results demonstrate that high-throughput approaches for screening synthetic lethal interactions in model organisms such as S. cerevisiae and S. pombecan serve as a valuable resource in helping to identify novel therapeutic targets in human cancer. [Table: see text]

The Novel H7N9 Influenza A Virus: Its Present Impact and Indeterminate Future

The Novel H7N9 Influenza A Virus: Its Present Impact and Indeterminate Future

The Golden Age of Molecular Ecology

The observations of different organisms’ interactions with their environment and with each other can probably be extended back to prehistoric times when humans became inquisitive about the conditions in which they lived and survived. This process became more “scientific” in Ancient Greece, when great philosophers of the time such as Aristotle, Hippocrates, and Herodotus provided first written evidence and descriptions of nature and the observable interactions among different animals and plants [1]. By now, while still a relatively young discipline, ecology has developed into a complex science that encompasses analyses of ecosystem biodiversity, spatial and temporal species distribution and dynamic fluctuation, cross-species interactions, and evolutionary processes in the environment. While the original ecological studies have been based on direct observation, the ecological disciplines have gradually involved the use of DNA and protein sequences in the evaluation of environmental diversity, community composition, evolutionary relationships, and species taxonomy. The use of molecular analyses has seen the largest impact in two areas, those of phylogenetic and biodiversity assessments. In both cases, by utilizing the general principle of molecular sequence conservation and gradual mutation over time, we can evaluate evolutionary relationships among species as well as reveal species identities by only analyzing select few DNA (or sometimes protein) sequences from each organism. Thus, current systematics and taxonomy no longer need to rely on the observations of species morphological and physiological characteristics but can rather use molecular phylogenetic information. Similarly, ecosystem biodiversity measurements should no longer have to rely on an exhaustive description and direct detection of all ecosystem inhabitants, but can rather employ DNA analysis to reveal who is present. The latter approach is especially effective for the studies of microbial communities, where cultivating and examining separately all individual members of the community is in many cases not practical.

Approaching the Functional Annotation of Fungal Virulence Factors Using Cross-Species Genetic Interaction Profiling

In many human fungal pathogens, genes required for disease remain largely unannotated, limiting the impact of virulence gene discovery efforts. We tested the utility of a cross-species genetic interaction profiling approach to obtain clues to the molecular function of unannotated pathogenicity factors in the human pathogen Cryptococcus neoformans. This approach involves expression of C. neoformans genes of interest in each member of the Saccharomyces cerevisiae gene deletion library, quantification of their impact on growth, and calculation of the cross-species genetic interaction profiles. To develop functional predictions, we computed and analyzed the correlations of these profiles with existing genetic interaction profiles of S. cerevisiae deletion mutants. For C. neoformans LIV7, which has no S. cerevisiae ortholog, this profiling approach predicted an unanticipated role in the Golgi apparatus. Validation studies in C. neoformans demonstrated that Liv7 is a functional Golgi factor where it promotes the suppression of the exposure of a specific immunostimulatory molecule, mannose, on the cell surface, thereby inhibiting phagocytosis. The genetic interaction profile of another pathogenicity gene that lacks an S. cerevisiae ortholog, LIV6, strongly predicted a role in endosome function. This prediction was also supported by studies of the corresponding C. neoformans null mutant. Our results demonstrate the utility of quantitative cross-species genetic interaction profiling for the functional annotation of fungal pathogenicity proteins of unknown function including, surprisingly, those that are not conserved in sequence across fungi.

Chimpanzee interactions with nonhuman species in an anthropogenic habitat

Interactions between wildlife species are numerous and diverse, ranging from commensalism to predation. Information on cross-species interactions in anthropogenic habitats are rare but can serve to improve our understanding of animal behavioural and ecological flexibility in response to human-induced changes. Here we report direct observations of interactions between chimpanzees (Pan troglodytes verus) and wild and domesticated species in a forest-farm mosaic at Bossou, Guinea, recorded between 1997 and 2009. The low diversity and abundance of wildlife, in particular typical chimpanzee prey species, are reflected in both the low interaction rates (one interaction per 400 observation hours) and the low number of species with which chimpanzees interacted (nine species, mostly mammals, but also birds and reptiles). Chimpanzees generally chose either to make direct physical contact with a species or not; interactions that involved direct contact lasted longer than noncontacts. Interactions with mammals showed the greatest diversity in nature and duration. Adults most often consumed a captured animal, while immatures most often engaged in playful behaviours with other species. Immatures also exhibited distinctive accompanying behaviours whereas adults rarely did so. Species-specific behaviours that depend on the age-class of the interactant are consistent with the idea that chimpanzees categorise different animals. We anticipate that chimpanzee interactions with sympatric species inhabiting humanised habitats will change over time to include more domesticated species. Conservation management strategies should anticipate behavioural flexibility in response to changing landscapes.

Implications of cross-species interactions on the temperature dependence of Kapitza conductance

We investigate the behavior of Kapitza conductance at interfaces between two Lennard-Jones fcc solids as a function of the range and strength of cross-species interactions via molecular dynamics simulations. It is found that decreasing either of these quantities leads to a reduction in the slope of linear temperature dependence of Kapitza conductance, suggesting a corresponding decrease in the probability of inelastic phonon-phonon interactions. To further explore the mechanisms responsible for such behavior, we calculate the phonon density of states and spectral temperature of each of the monolayers adjacent to the interface. It is found that the reduction of the range and strength of cross-species interactions leads to a softening of the density of states near the interface, while the spectral temperature calculations provide further evidence that such reductions decrease the probability of inelastic phonon scattering. These findings help explain varying accounts of the temperature dependence of Kapitza conductance observed in previous works.

Optimization and validation of the SNP forID 34-SNPplex for POP7™

The SNP forID 34-SNPplex is a multiplex of ancestry informative single nucleotide polymorphism markers and was originally designed for POP6™ polymer gels. Due to the higher viscosity of POP7™, a different design is necessary to resolve peaks smaller than 40 bp when this type of polymer gel is used. The single original SNaPshot™ assay was separated and redesigned into two individual multiplex SNaPshot™ assays in which rs2304925 was moved in between two SNPs with larger amplicons. Minor adjustments to PCR parameters and primer concentrations further reduced noise background in comparison with the original protocol. Validation of the assay included reproducibility (100%), sensitivity (complete DNA-profiles up to 0.5 ng) and specificity studies (no cross-species interaction). A population study ( n = 145), including 46 Belgian samples, further validated the assay for future forensic use.

Human PD-L1-overexpressing porcine vascular endothelial cells induce functionally suppressive human CD4+CD25hiFoxp3+ Treg cells

In xenotransplantation models, direct activation of hCD4(+) T cells by porcine VECs leads to a robust proliferation of T cells. To investigate the underlying mechanisms, human antiporcine MLEC culture was used to investigate cross-species cell interactions, proliferation of hCD4(+) T cells, and induction of human cytokines. We report that xenoantigen presentation by PIEC expands hCD4(+) Foxp3(+) Tregs and hCD4(+) Foxp3(-) Teffs, and this process is dependent on porcine MHC-II antigen expression. Stable transfection of hPD-L1 into PIEC inhibits Teff proliferation, but Treg proliferation is not affected. Surprisingly, IL-10 production by hCD4(+) T cells is augmented significantly by PIEC(hPD-L1). Notably, hPD-L1-induced Tregs have higher suppressive potency and mediate suppressive function partially through IL-10 and CD73. This study opens the possibility of using hPD-L1-overexpressing porcine VECs as a novel therapeutic to allow tolerance of xenotransplants and also supports the possibility of using hPD-L1 transgenic pigs as xenotransplant donors.

Cross-Species Induction of Antimicrobial Compounds, Biosurfactants and Quorum-Sensing Inhibitors in Tropical Marine Epibiotic Bacteria by Pathogens and Biofouling Microorganisms

Enhancement or induction of antimicrobial, biosurfactant, and quorum-sensing inhibition property in marine bacteria due to cross-species and cross-genera interactions was investigated. Four marine epibiotic bacteria (Bacillus sp. S3, B. pumilus S8, B. licheniformis D1, and Serratia marcescens V1) displaying antimicrobial activity against pathogenic or biofouling fungi (Candida albicans CA and Yarrowia lipolytica YL), and bacteria (Pseudomonas aeruginosa PA and Bacillus pumilus BP) were chosen for this study. The marine epibiotic bacteria when co-cultivated with the aforementioned fungi or bacteria showed induction or enhancement in antimicrobial activity, biosurfactant production, and quorum-sensing inhibition. Antifungal activity against Y. lipolytica YL was induced by co-cultivation of the pathogens or biofouling strains with the marine Bacillus sp. S3, B. pumilus S8, or B. licheniformis D1. Antibacterial activity against Ps. aeruginosa PA or B. pumilus BP was enhanced in most of the marine isolates after co-cultivation. Biosurfactant activity was significantly increased when cells of B. pumilus BP were co-cultivated with S. marcescens V1, B. pumilus S8, or B. licheniformis D1. Pigment reduction in the quorum-sensing inhibition indicator strain Chromobacterium violaceum 12472 was evident when the marine strain of Bacillus sp. S3 was grown in the presence of the inducer strain Ps. aeruginosa PA, suggesting quorum-sensing inhibition. The study has important ecological and biotechnological implications in terms of microbial competition in natural environments and enhancement of secondary metabolite production.

Characterization of canine coagulation factorVII and its complex formation with tissue factor: canine-human cross-species compatibility.

Canine models have been good predictors of efficacy of hemophilia treatments, including recombinant human coagulation factor (F)VIIa (hFVIIa). However, canine FVIIa and tissue factor (TF) have remained incompletely characterized. To explore canine-human cross-species FVIIa-TF compatibility in order to strengthen the predictive value of canine models in research on FVIIa and TF. Canine FVIIa (cFVIIa) and canine TF((1-217)) [cTF((1-217))] were produced by recombinant techniques, and canine-human cross-species FVIIa-TF interactions were characterized in vitro. Recombinant cFVIIa and soluble cTF((1-217)) were produced and purified to homogeneity. hFVIIa and cFVIIa bound with comparably high affinities to cTF((1-217)) (K(D)=6.0±0.7 nm and K(D)=6.0±0.3 nm, respectively) and to cell surface-expressed cTF (K(D)=8.4±0.4 nm and K(D)=7.2±1.2 nm, for (125) I-labeled hFVIIa and cFVII, respectively). In contrast, cFVIIa bound to human TF (hTF) with decreased affinity, both in solution and on cell surfaces. The decreased binding resulted in reduced activity of cFVIIa in functional assays with hTF((1-209)) . In direct comparison, cFVIIa was more active than hFVIIa, both in the absence and the presence of cognate TF. The present finding that hFVIIa binds to cTF essentially as it does to hTF substantiates the hypothesis that human FVIIa-TF biology can be reliably recapitulated in canine models on administration of hFVIIa to dogs.

Quantitative Genetic Interactions Reveal Biological Modularity

Traditionally, research has been reductionist, characterizing the individual components of biological systems. But new technologies have increased the size and scope of biological data, and systems approaches have broadened the view of how these components are interconnected. Here, we discuss how quantitative mapping of genetic interactions enhances our view of biological systems, allowing their deeper interrogation across different biological scales.

Rat CC chemokine receptor 4 is the functional homologue of human CC chemokine receptor 4 and can interact with human CCL17 and CCL22

Human CCL17/TARC (hCCL17) and CCL22/MDC (hCCL22) interact with their receptor CCR4, playing pivotal roles in various Th2 cell-dominant diseases. Rat Ccl17, Ccl22 and Ccr4 share 63.4%, 65.2% and 87.5% homology at the amino acid level, respectively, compared with their human homologues. Rat Ccl22 has been demonstrated to interact with rat Ccr4. However, it is not known whether rat Ccl17 is a functional ligand for rat Ccr4 and whether rat Ccr4 can interact with hCCL17 and hCCL22. In this study, we cloned rat Ccl17 and Ccr4 cDNA from rat thymus and expressed the recombinant rat Ccl17. The binding assay indicated rat Ccl17 could saturably bind rat Ccr4, and this binding could be competitively inhibited by unlabeled rat Cc17, hCCL17 or hCCL22. Both rat and human CCL17 or CCL22 could induce the chemotactic migration and calcium mobilization in rat Ccr4-transfected cells. They could also desensitize each other’s effect on chemotaxis and calcium mobilization. Furthermore, both rat Ccl17 and hCCL17 could induce significant receptor internalization in rat Ccr4-EGFP transfected cells. These results demonstrated the conserved CCL17/CCR4 interaction in rats and the further cross-species interaction of rat Ccr4 with hCCL17 and hCCL22. Likewise, they provided the molecular basis for the investigation of physiological and pharmacological roles of CCR4, its ligands, and their antagonists in rat disease models.

A theory for the arrangement of sensory organs inDrosophila

We study the arrangements of recurved bristles on the anterior wing margin of wild-type and mutant Drosophila. The epidermal or neural fate of a proneural cell depends on the concentrations of proteins of the achaete-scute complex. At puparium formation, concentrations of proteins are nearly identical in all cells of the anterior wing and each cell has the potential for neural fate. In wild-type flies, the action of regulatory networks drives the initial state to one where a bristle grows out of every fifth cell. Recent experiments have shown that the frequency of recurved bristles can be made to change by adjusting the mean concentrations of the zinc-finger transcription factor Senseless and the micro-RNA miR-9a. Specifically, mutant flies with reduced levels of miR-9a exhibit ectopic bristles, and those with lower levels of both miR-9a and Senseless show regular organization of recurved bristles, but with a lower periodicity of 4. We argue that these characteristics can be explained assuming an underlying Turing-type bifurcation whereby a periodic pattern spontaneously emerges from a uniform background. However, bristle patterns occur in a discrete array of cells, and are not mediated by diffusion. We argue that intracellular actions of transmembrane proteins such as Delta and Notch can play a role of diffusion in destabilizing the homogeneous state. In contrast to diffusion, intercellular actions can be activating or inhibiting; further, there can be lateral cross-species interactions. We introduce a phenomenological model to study bristle arrangements and make several model-independent predictions that can be tested in experiments. In our theory, miRNA-9a is one of the components of the underlying network and has no special regulatory role. The loss of periodicity in its absence is due to the transfer of the system to a bistable state.