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BackgroundAsthma has been associated with impaired interferon response. Multiple cell types have been implicated in such response impairment and may be responsible for asthma immunopathology. However, existing models to study the immune response in asthma are limited by bulk profiling of cells. Our objective was to Characterize a model of peripheral blood mononuclear cells (PBMCs) of patients with severe asthma (SA) and its response to the TLR3 agonist Poly I:C using two single-cell methods.MethodsTwo complementary single-cell methods, DropSeq for single-cell RNA sequencing (scRNA-Seq) and mass cytometry (CyTOF), were used to profile PBMCs of SA patients and healthy controls (HC). Poly I:C-stimulated and unstimulated cells were analyzed in this study.ResultsPBMCs (n = 9414) from five SA (n = 6099) and three HC (n = 3315) were profiled using scRNA-Seq. Six main cell subsets, namely CD4 + T cells, CD8 + T cells, natural killer (NK) cells, B cells, dendritic cells (DCs), and monocytes, were identified. CD4 + T cells were the main cell type in SA and demonstrated a pro-inflammatory profile characterized by increased JAK1 expression. Following Poly I:C stimulation, PBMCs from SA had a robust induction of interferon pathways compared with HC. CyTOF profiling of Poly I:C stimulated and unstimulated PBMCs (n = 160,000) from the same individuals (SA = 5; HC = 3) demonstrated higher CD8 + and CD8 + effector T cells in SA at baseline, followed by a decrease of CD8 + effector T cells after poly I:C stimulation.ConclusionsSingle-cell profiling of an in vitro model using PBMCs in patients with SA identified activation of pro-inflammatory pathways at baseline and strong response to Poly I:C, as well as quantitative changes in CD8 + effector cells. Thus, transcriptomic and cell quantitative changes are associated with immune cell heterogeneity in this model to evaluate interferon responses in severe asthma.

Rationale: MicroRNAs are potent regulators of biologic systems that are critical to tissue homeostasis. Individual microRNAs have been identified in airway samples. However, a systems analysis of the microRNA–mRNA networks present in the sputum that contribute to airway inflammation in asthma has not been published. Objectives: Identify microRNA and mRNA networks in the sputum of patients with asthma. Methods: We conducted a genome-wide analysis of microRNA and mRNA in the sputum from patients with asthma and correlated expression with clinical phenotypes. Weighted gene correlation network analysis was implemented to identify microRNA networks (modules) that significantly correlate with clinical features of asthma and mRNA expression networks. MicroRNA expression in peripheral blood neutrophils and lymphocytes and in situ hybridization of the sputum were used to identify the cellular sources of microRNAs. MicroRNA expression obtained before and after ozone exposure was also used to identify changes associated with neutrophil counts in the airway. Measurements and Main Results: Six microRNA modules were associated with clinical features of asthma. A single module (nely) was associated with a history of hospitalizations, lung function impairment, and numbers of neutrophils and lymphocytes in the sputum. Of the 12 microRNAs in the nely module, hsa-miR-223-3p was the highest expressed microRNA in neutrophils and was associated with increased neutrophil counts in the sputum in response to ozone exposure. Multiple microRNAs in the nely module correlated with two mRNA modules enriched for TLR (Toll-like receptor) and T-helper cell type 17 (Th17) signaling and endoplasmic reticulum stress. hsa-miR-223-3p was a key regulator of the TLR and Th17 pathways in the sputum of subjects with asthma. Conclusions: This study of sputum microRNA and mRNA expression from patients with asthma demonstrates the existence of microRNA networks and genes that are associated with features of asthma severity. Among these, hsa-miR-223-3p, a neutrophil-derived microRNA, regulates TLR/Th17 signaling and endoplasmic reticulum stress.

Additional file 2. Additional figures.

BackgroundAsthma has been associated with impaired interferon responses. Multiple cell types have been implicated in these impaired responses and may be responsible for increased exacerbations and immunopathology of asthma.ObjectiveCharacterize the single-cell response to Poly I:C of peripheral blood mononuclear cells (PBMCs) of patients with severe asthma (SA).MethodsTwo complementary single-cell methods, DropSeq for single-cell RNA sequencing (scRNA-Seq) and mass cytometry (CyTOF), were used to profile PBMCs of SA and healthy controls (HC). Poly I:C and unstimulated cells were analyzed in this study.ResultsPBMCs (n=9,414) from five SA (n=6,099) and three HC (n=3,315) were profiled using scRNA-Seq. Six main cell subsets, including CD4+ T cells, CD8+ T cells, natural killer (NK) cells, B cells, dendritic cells (DCs), and monocytes, were identified. CD4+ T cells were the main cell type and demonstrated a pro-inflammatory profile characterized by increasedJAK1expression in unstimulated cells. Following Poly I:C stimulation, PBMCs from SA had a robust induction of interferon pathways compared with HC. Additional analyses to identify core regulators of the enhanced interferon response in SA identifiedIRF1, STAT1, IRF7, STAT2, andIRF9. CyTOF profiling of Poly I:C and unstimulated PBMCs (n=120,000) from the same individuals (SA=4; HC=2) demonstrated higher numbers of CD8+ effector cells and Th1 CD4+ T cells in unstimulated conditions, followed by a decrease of these two cell subsets after poly I:C stimulation.ConclusionSingle-cell profiling of PBMCs with scRNA-seq and CyTOF in patients with SA identified activation of pro-inflammatory pathways at baseline and strong response to Poly I:C, as well as quantitative changes in CD8+ effector cells and Th1 cells. Thus, transcriptomic and cell quantitative changes are associated with immune cell heterogeneity in severe asthma.Key Messages-Single-cell RNA sequencing identified a pro-inflammatory status in unstimulated PBMCs of severe asthmatics.-Mass cytometry identified quantitative differences in CD8+ effector cells and Th1 cells of severe asthmatics.-The response to Poly I:C stimulation, an interferon agonist, was not impaired in a subgroup of patients with severe asthma.Capsule summarySingle-cell profiling of PBMCs in severe asthmatics characterized gene expression responses to an interferon agonist and quantitative differences in distinct cell populations. Comprehensive single-cell immune may help identify key cell features responsible for asthma heterogeneity.

This study is concerned with the role of a fin-and-tube heat exchanger in modifying microbial indoor air quality. Specifically, depositional losses of ambient bioaerosols and particles onto dry (not cooled) and wet (cool) coil surfaces were measured for different airspeeds passing through the test coil. Total, bacterial and fungal DNA concentrations in condensate water produced by a wet coil were also quantified by means of fluorescent dsDNA-binding dye and qPCR assays. Results revealed that the deposition of bioaerosols and total particles is substantial on coil surfaces, especially when wet and cool. The average deposition fraction was 0.14 for total DNA, 0.18 for bacterial DNA and 0.22 for fungal DNA on the dry coil, increasing to 0.51 for total DNA, 0.50 for bacterial DNA and 0.68 for fungal DNA on the wet coil. Overall, as expected, deposition fractions increased with increasing particle size and increasing airspeed. Deposited DNA was removed from the cooling coil surfaces through the flow of condensing water at a rate comparable to the rate of direct deposition from air. A downward trend of bacterial and fungal DNA measured in condensate water over time provides suggestive evidence of biological growth on heat exchangers during nonoperational times of a ventilation system. This investigation provides new information about bioaerosol deposition onto a conventional fin-and-tube cooling coil, a potentially important factor influencing indoor exposure to microbial aerosols in air-conditioned buildings.

Fan-coil units (FCUs) see wide applications in buildings but few are integrated with high-quality filters for efficient particle removal. Driven by an attempt to protect the indoor space served by FCUs from elevated outdoor PM concentrations (e.g. periodic haze events in Southeast Asia), four different grades of filters (dust-spot efficiencies of 25%, 65%, 85% and 95%, denoted as F 25 , F 65. F 85 , and F 95 hereafter) were installed inside the cassette FCUs respectively in four similar rooms. Air exchange was controlled by the recirculation fans in FCUs and exfiltration via door gaps. Performance of the filters was evaluated through continuous monitoring of particle number concentrations. Energy consumption and noise levels were also recorded via field measurements. The overall particle removal efficiencies (via filter-integrated FCUs) generally increased with higher filter grades; however, F 95 didn't provide a significant improvement over F 85 . Upgrading from F 25 to F 85 or F 95 decreased the size-resolved particle I/O ratios significantly (from 0.19 to 0.65 to 0.06–0.24 depending on the particle sizes). Installation of F 85 or F 95 alone was not sufficient to reduce the indoor PM 2.5 concentrations to the WHO guideline of 25 μg m −3 under moderate and heavy haze scenarios. F 85 resulted in the lowest energy consumption in terms of chilled water energy and FCU electricity combined. F 95 application led to the highest noise level at ∼46.6 dBA. The study advances the knowledge of particle attenuation effects by the FCU with different grades of filters and provides a basis for filter selection against compromised outdoor conditions in similar settings.

Multiple studies have been dedicated to particle emissions from three dimensional printer (3D printer). They collectively have shown that 3D printers will emit significant ultrafine particles during their printing processes. An important step forward is to investigate the printing process in detail and help reducing emissions. This study investigates particle emissions from two filaments of acrylonitrile butadiene styrene (ABS) and polylactic acid (PLA) according to four steps (loading, heating, printing, and unloading) during the 3D printing process in constraint of product quality assessment. The results show that ABS filament triggers at least times higher particle emissions than PLA filament (ABS-printed product presents higher quality with higher nozzle temperature (240 °C); however, higher nozzle temperature triggers substantially higher particle emission. This study further identifies that the particle emissions are mostly triggered by the heating process rather than the printing process. It indicates that filament undergoes decomposition during the heating period after being loading into the extruder. As for product quality in terms of surface roughness and production deformation, ABS is not compatible to fast neither printing speed nor low nozzle temperature; the PLA filament exhibits significant tolerance to temperature and feed rate changes. An optimization, which is externally heating up both the extruder and platform before the filament is loaded, shows that pre-heating reduces particle emissions by 75% for ABS filament when compared with the conventional procedure.

For an air source heat pump (ASHP) unit with a vertically installed multi-circuit outdoor coil, it is rarely possible to make the frost accumulations on each circuit's surface equal, leading to different frosting evenness values (FEVs) as a reverse cycle defrosting operation starts. On the other hand, uneven defrosting phenomenon was found and reported as many methods were developed to improve defrosting performance of ASHP systems, which may be attributable to the reverse cycle defrosting starting at an uneven frosting. Understanding of defrosting performance of an ASHP unit with a multi-circuit outdoor coil at different FEVs is of importance for ASHP units' application, but studies are scarce in the open literatures. In this paper, we report an experimental study on defrosting performance when frost accumulated on the surface of outdoor coil at different FEVs. This paper presents details of an experimental ASHP unit and the experimental conditions, followed by results, and conclusions. Finally, an increase of 6.8% in defrosting efficiency was confirmed when the FEV changed from 82.6% to 96.6%.

Estimates of population exposure to ambient air pollution traditionally rely on concentrations measured at central-site monitors as a surrogate for concentrations to which people are exposed. In this study of Singapore, we estimate population-averaged exposure concentrations for PM2.5, PM10, and O3 by applying a model and data that account for age and gender demographics, intraurban regional variability, and microenvironmental effects with age- and gender-stratified time-activity budgets. The study addresses exposure only to air pollutants of outdoor origin. Spatially averaged midpoint estimates of lifetime ambient exposure concentrations are 59%, 52%, and 47% of outdoor concentrations for PM2.5, PM10, and O3, respectively. Utilizing ambient data for calendar year 2007, we estimate that intraurban variability in ambient concentration results in lifetime-integrated exposure concentrations in the respective ranges of 10-14μgm-3 for PM2.5, 14-18μgm-3 for PM10, and 7.5-15μgm-3 for O3. Uncertainty in estimates of the indoor proportion of outdoor pollutants, which are input to the model, results in greater variability than do intraurban differences in ambient concentrations, resulting in respective ranges of 6.6-15μgm-3 for PM2.5, 8.1-21μgm-3 for PM10 and 6.8-16μgm-3 for O3. Estimates of time spent in naturally ventilated (NV) homes are in the range 10-13h/d across the population and exposures in NV homes contribute 49%, 53%, and 56% of total exposure for PM2.5, PM10 and O3, of outdoor origin, respectively. Results illustrate the importance of accurately characterizing climate-specific indoor-outdoor pollutant relationships to better quantify human exposure to air pollutants. NRF (Natl Research Foundation, S’pore) Accepted version

As a commercially important species in East Asia, the natural resources of Scapharca broughtonii have been suffering from severe population decline across its main habitats. In China, recovery efforts for S. broughtonii are in progress. To provide scientific bases for fisheries management and conservation program, genetic diversity and population structure of seven wild populations of S. broughtonii from the northern China coast was assessed using seven microsatellite loci in this study. High genetic diversity was present in all the seven populations, as observed in mean allelic richness per locus (11.3–12.5), and average expected heterozygosity (0.835–0.867). No significant difference in allelic richness or expected heterozygosity was observed among the seven populations. Pairwise FST estimates and NJ tree topologies based on DC distances indicated that the seven populations fell into two groups, showing a clear division between the populations from the south and north of the Shandong Peninsula. Genetic differentiation was further analyzed using AMOVA and assignation tests. Genetic barrier analysis using Monmonier algorithm also confirmed that the Shandong Peninsula was the putative barrier separating the northern and southern populations. In addition, marine currents probably play an important role in high gene flow among three populations from the same marine gyre.

It is getting more popular to use desktop 3D printers either at homes or offices, which may emit a large amount of particles when in use. This work aims to obtain accurate size-resolved particle emission rates from both single and two desktop 3D printers in a ten–thousand-level clean room, with acrylonitrile butadiene styrene (ABS) for the feedstock. Particle concentrations were measured at three different spots in the clean room. We found that the major size of particles produced by the 3D printers is less than 10 μm (PM 10 ). The further it is from the printer, the higher the particle concentrations are. Moreover, the smaller the size of particles, the higher the concentration of particles, with the size ranged from 0.25 μm to 0.28 μm corresponding to the highest concentration. The maximum value of particle concentration is around 2.5×10 4 /L for single printer and 4×10 4 /L for two printers.

Summary Heat tolerance is a complex and economically important trait for catfish genetic breeding programs. With global climate change, it is becoming an increasingly important trait. To better understand the molecular basis of heat stress, a genome-wide association study (GWAS) was carried out using the 250 K catfish SNP array with interspecific backcross progenies, which derived from crossing female channel catfish with male F1 hybrid catfish (female channel catfish × male blue catfish). Three significant associated SNPs were detected by performing an EMMAX approach for GWAS. The SNP located on linkage group 14 explained 12.1% of phenotypical variation. The other two SNPs, located on linkage group 16, explained 11.3 and 11.5% of phenotypical variation respectively. A total of 14 genes with heat stress related functions were detected within the significant associated regions. Among them, five genes—TRAF2, FBXW5, ANAPC2, UBR1 and KLHL29— have known functions in the protein degradation process through the ubiquitination pathway. Other genes related to heat stress include genes involved in protein biosynthesis (PRPF4 and SYNCRIP), protein folding (DNAJC25), molecule and iron transport (SLC25A46 and CLIC5), cytoskeletal reorganization (COL12A1) and energy metabolism (COX7A2, PLCB1 and PLCB4) processes. The results provide fundamental information about genes and pathways that is useful for further investigation into the molecular mechanisms of heat stress. The associated SNPs could be promising candidates for selecting heat-tolerant catfish lines after validating their effects on larger and various catfish populations.

© 2016 Elsevier Ltd. Particles released from biomass burning can contribute to severe air pollution. We monitored indoor and outdoor particles in a mechanically ventilated and air-conditioned building during and after the 2013 haze event in Singapore. Continuous monitoring of time-and size-resolved particles in the diameter range 0.01-10 μm was conducted for two weeks in each sampling campaign. During the haze event, the averaged size-resolved outdoor particle volume concentrations (dV/d(logDp)) for diameters larger than 0.3 μm were considerably higher than those during the post-haze days (9-185 μm3cm-3versus 1-35 μm3cm-3). However, the average number concentration of particles with diameters in the range 10-200 nm was substantially lower on the hazy days than on the post-haze days (11,400 to 14,300 particles cm-3for hazy days, versus an average of 23,700 particles cm-3on post-haze days). The building mechanical ventilation system, equipped with MERV 7 filters, attenuated the penetration and persistence of outdoor particles into the monitored building. Indoor particle concentrations, in the diameter ranges 0.3-1.0 μm and 1.0-2.5 μm, closely tracked the corresponding patterns of outdoor particle concentrations. For particles in the size range 0.01-1.0 μm, the size-resolved mean indoor/outdoor (I/O) ratios were in the range 0.12-0.65 with the highest mean I/O ratio at 0.3 μm (0.59 in AC on mode and 0.64 in AC off mode). The air conditioning and mechanical ventilation system with MERV 7 filters provided low single-pass removal efficiency (less than ~ 30%) for particles with diameters of 0.01-1.0 μm. During the haze, for particles larger than ~0.2 μm, lower I/O ratios and higher removal efficiencies occurred with the air conditioning operating as compared to with mechanical ventilation only. This observation suggests the possibility of particle loss to air conditioning system surfaces, possibly enhanced by thermophoretic or diffusiophoretic effects.

We conducted multiday continuous monitoring of indoor and outdoor particulate matter (PM) in classrooms with fan-assisted natural ventilation (NV) at five primary schools in Singapore. We monitored size-resolved number concentration of PM with diameter 0.3-10 μm at all schools and alveolar deposited surface area concentrations of PM with diameter 0.01-1.0 μm (SA0.01-1.0) at two schools. Results show that, during the monitoring period, schools closer to expressways and in the downtown area had 2-3 times higher outdoor PM0.3-1.0 number concentrations than schools located in suburban areas. Average indoor SA0.01-1.0 was 115-118 μm(2) cm(-3) during periods of occupancy and 72-87 μm(2) cm(-3) during unoccupied periods. There were close indoor and outdoor correlations for fine PM during both occupied and unoccupied periods (Pearson's r = 0.84-1.0) while the correlations for coarse PM were weak during the occupied periods (r = 0.13-0.74). Across all the schools, the size-resolved indoor/outdoor PM ratios (I/O ratios) were 0.81 to 1.58 and 0.61 to 0.95 during occupied and unoccupied periods, respectively, and average infiltration factors were 0.64 to 0.94. Average PM net emission rates, calculated during periods of occupancy in the classrooms, were lower than or in the lower range of emission rates reported in the literature. This study also reveals that indoor fine and submicron PM predominantly come from outdoor sources, while indoor sources associated with occupancy may be important for coarse PM even when the classrooms have high air exchange rates.

Interspecific hybrids provide a rich source for the analysis of allele-specific expression (ASE). In this work, we analyzed ASE in F1 hybrid catfish using RNA-Seq datasets. While the vast majority of genes were expressed with both alleles, 7–8 % SNPs exhibited significant differences in allele ratios of expression. Of the 66,251 and 177,841 SNPs identified from the datasets of the liver and gill, 5420 (8.2 %) and 13,390 (7.5 %) SNPs were identified as significant ASE-SNPs, respectively. With these SNPs, a total of 1519 and 3075 ASE-genes were identified. Gene Ontology analysis revealed that genes encoding cytoplasmic ribosomal proteins (RP) were highly enriched among ASE genes. Parent-of-origin was determined for 27 and 30 ASE RP genes in the liver and gill, respectively. The results indicated that genes from both channel catfish and blue catfish were involved in ASE. However, each RP gene appeared to be almost exclusively expressed from only one parent, indicating that ribosomes in the hybrid catfish were in the “hybrid” form. Overall representation of RP transcripts among the transcriptome appeared lower in the F1 hybrid catfish than in channel catfish or blue catfish, suggesting that the “hybrid” ribosomes may work more efficiently for translation in the F1 hybrid catfish.

Nitric oxide is well known for its roles in immune responses. As such, its synthesizing enzymes have been extensively studied from various species including some teleost fish species. However, the NOS genes have not been characterized in channel catfish (Ictalurus punctatus). In this study, we identified and characterized three NOS genes including one NOS1 and two NOS2 genes in channel catfish. Comparing with the NOS genes from other fish species, the catfish NOS genes are highly conserved in their structural features. Phylogenetic and syntenic analyses allowed determination of NOS1 and NOS2 genes of channel catfish and their orthology relationships. Syntenic analysis, as well as the phylogenetic analysis, indicated that the two NOS2 genes of catfish were lineage-specific duplication. The NOS genes were broadly expressed in most tested tissues, with NOS1 being expressed at the highest levels in the brain, NOS2b1 highly expressed in the skin and gill, and NOS2b2 lowly expressed in most of the tested tissues. The most striking findings of this study was that the expression of the NOS genes are highly regulated after bacterial infection, with time-dependent expression patterns that parallel the migration of macrophages. After Edwardsiella ictaluri challenge, dramatically different responses among the three NOS genes were observed. NOS1 was only significantly in the skin early after infection, while NOS2b1 was rapidly upregulated in gill, but more up-regulated in trunk kidney with the progression of the disease, suggesting such differences in gene expression may be reflective of the migration of macrophages among various tissues of the infected fish. In contrast to NOS1 and NOS2b1, NOS2b2 was normally expressed at very low levels, but it is induced in the brain and liver while significantly down-regulated in most other tissues.

Channel catfish (Ictalurus punctatus) has been recognized as a dominant freshwater aquaculture species in the United States. It is also a suitable model for studying the mechanisms of sex determination and differentiation because of its sexual plasticity and exhibition of both genetic and environmental sex determination. The testicular differentiation in male channel catfish normally starts between 90 and 102 days postfertilization (dpf), while the ovarian differentiation starts early from 19 dpf. As such, efforts to better understand the postponed testicular development at the molecular level are needed. Toward that end, we conducted transcriptomic comparison of gene expression of male and female gonads at 90, 100, and 110 dpf using high-throughput RNA-Seq. Transcriptomic profiles of male gonads on 90 and 100 dpf exhibited high similarities except for a small number of significantly up-regulated genes that were involved in development of germ cell-supporting somatic cells, while drastic changes were observed during 100–110 dpf, with a group of highly up-regulated genes that were involved in germ cells development, including nanog and pou5f1. Transcriptomic comparison between testes and ovaries identified male-preferential genes, such as gsdf, cxcl12, as well as other cytokines mediated the development of the gonad into a testis. Co-expression analysis revealed highly correlated genes and potential pathways underlying germ cell differentiation and spermatogonia stem cell development. The candidate genes and pathways identified in this study set the foundation for further studies on sex determination and differentiation in catfish as well as other teleosts.

Poorly operated air conditioning and mechanical ventilation (ACMV) system might cause significant Sick Building Syndrome (SBS) symptoms and thermal discomfort in the hot and humid climate. This study presents our investigations on the prevalence of SBS symptoms and thermal comfort in offices in Singapore via two approaches including: (1) the onsite objective monitoring and questionnaire-based investigation under normal ACMV practices, and (2) the online survey with occupants in controlled indoor temperatures. The results indicate that the prevalence of individual SBS symptoms is lower than the similar studies in other geographic regions. Overcooling seems to be the domineering complaint in the local context and the occupants seem to prefer higher indoor temperature. As such, human behavioral adjustments such as adding clothing happen quite frequently. Moreover, the data also suggests that cultural traits might skew the survey results, especially in certain subjective aspects regarding the satisfactory level and comfort. To sum up, the prevalence of SBS symptoms are generally acceptable in current local context. However, due to the hot and humid ambient environment, traditional ACMV system with vapor compression refrigerant tends to trigger the overcooling issue in relation to the sensible and latent heat. It is invaluable to advance our understanding of the relationships between the ACMV system, human behavioral adjustments, and building energy consumptions in the tropical region.

Background Columnaris causes severe mortalities among many different wild and cultured freshwater fish species, but understanding of host resistance is lacking. Catfish, the primary aquaculture species in the United States, serves as a great model for the analysis of host resistance against columnaris disease. Channel catfish in general is highly resistant to the disease while blue catfish is highly susceptible. F2 generation of hybrids can be produced where phenotypes and genotypes are segregating, providing a useful system for QTL analysis. To identify genes associated with columnaris resistance, we performed a genome-wide association study (GWAS) using the catfish 250 K SNP array with 340 backcross progenies derived from crossing female channel catfish (Ictalurus punctatus) with male F1 hybrid catfish (female channel catfish I. punctatus × male blue catfish I. furcatus). Results A genomic region on linkage group 7 was found to be significantly associated with columnaris resistance. Within this region, five have known functions in immunity, including pik3r3b, cyld-like, adcyap1r1, adcyap1r1-like, and mast2. In addition, 3 additional suggestively associated QTL regions were identified on linkage groups 7, 12, and 14. The resistant genotypes on the QTLs of linkage groups 7 and 12 were found to be homozygous with both alleles being derived from channel catfish. The paralogs of the candidate genes in the suggestively associated QTL of linkage group 12 were found on the QTLs of linkage group 7. Many candidate genes on the four associated regions are involved in PI3K pathway that is known to be required by many bacteria for efficient entry into the host. Conclusion The GWAS revealed four QTLs associated with columnaris resistance in catfish. Strikingly, the candidate genes may be arranged as functional hubs; the candidate genes within the associated QTLs on linkage groups 7 and 12 are not only co-localized, but also functionally related, with many of them being involved in the PI3K signal transduction pathway, suggesting its importance for columnaris resistance.