Biology subjects

Bartley, K.

Publications and source records attributed to Bartley, K..

4 recordsLinked to original sources

bioRxiv2025

Over-expression and increased copy numbers of a cytochrome P450 and two UDP-glucuronosyltransferase genes in macrocyclic lactone resistant Psoroptes ovis of cattle

Psoroptes ovis is a mite species that feeds on sheep, cattle, other ungulates, rabbits, and horses, which can develop into a severe exudative dermatitis known as psoroptic mange. The macrocyclic lactone (ML) family of acaricides are commonly used to control psoroptic mange. However, certain strains of cattle and sheep mites have developed resistance against MLs, which has led to reduced treatment efficacy and even treatment failure. Here we investigated the genetic basis of ML resistance in mites collected from cattle across Belgium. We compared gene expression between susceptible and resistant mites before and after exposure to ivermectin and genetic diversity between a single susceptible and resistant populations. We generated chromosomal genome assemblies of Psoroptes ovis derived from sheep and cattle respectively and correlated genomic diversity of susceptible and resistant mite populations sampled across Belgium. Gene expression data revealed constitutive over-expression of a cytochrome P450 monooxygenase (CYP) gene and two tandemly located UDP-glucuronosyltransferase (UGT) genes among others. On investigation of the genomic data, we observed copy number variation at both loci in population genomic data. The CYP gene is not amplified in the susceptible population but occurs in multiple copies in all resistant populations and is associated with a peak in Fst between resistant and susceptible populations indicative of selection. By contrast, the two UGT genes are massively and tandemly amplified in all populations including the susceptible dataset with a weaker associated signal of selection than the amplified CYP. Hence, distinct mechanisms of amplification and gene regulation are occurring at these putative resistance loci in P. ovis. Author SummaryFor the first time, we investigated the genetic basis of resistance in scab mites to a key family of drugs (Macrocyclic Lactones) used to control this parasite. Scab mite infestations can cause serious welfare issues in affected cattle and sheep with associated economic impact on production. To identify genes associated with resistance, we applied a combination of approaches including targeted sequencing of candidate genes, genome sequencing and gene expression comparisons of resistant mites with mites that are still susceptible to treatment. We were able to rule-out one family of candidate genes but identified very high expression of genes from two gene families that metabolise, and thereby detoxify, the treatment drug in resistant mites. On examination of the genomic context of these genes we found that the genes had undergone an increase in copy number in the resistant mites compared to the susceptible mites. With our now much increased understanding of resistance in scab mites we can track the spread of resistance using markers in these genes present in resistant mites. We can also now test the suitability of alternative treatments that restore the lethality of Macrocyclic Lactones in scab mites, mitigating the damaging effects of resistance in this species.

genomics↗

bioRxiv2021

A Rickettsiella endosymbiont is a potential source of essential B-vitamins for the poultry red mite, Dermanyssus gallinae

Obligate blood-sucking arthropods rely on symbiotic bacteria to provision essential B vitamins that are either missing or at sub-optimal amounts in their nutritionally challenging blood diet. The poultry red mite Dermanyssus gallinae, an obligate blood-feeding ectoparasite, is primarily associated with poultry and a serious threat to the hen egg industry. Thus far, the identity and biological role of nutrient provisioning bacterial mutualists from D. gallinae are little understood. Here, we demonstrate that a Rickettsiella Gammaproteobacteria in maternally transmitted in D. gallinae and universally present in D. gallinae mites collected at different sites throughout Europe. In addition, we report the genome sequence of uncultivable endosymbiont "Candidatus Rickettsiella rubrum" from D. gallinae eggs. The endosymbiont has a circular 1. 89 Mbp genome that encodes 1973 protein. Phylogenetic analysis confirms the placement R. rubrum within the Rickettsiella genus, closely related to a facultative endosymbiont from the pea aphid and Coxiella-like endosymbionts from blood feeding ticks. Analysis of the R. rubrum genome reveals many protein-coding sequences are either pseudogenized or lost, but R. rubrum has retained several B vitamin biosynthesis pathways, confirming the importance of these pathways in evolution of its nutritional symbiosis with D. gallinae. In silico metabolic pathway reconstruction revealed that R. rubrum is unable to synthesise protein amino acids and therefore these nutrients are likely provisioned by the host. In contrast R. rubrum retains biosynthetic pathways for B vitamins: thiamine (vitamin B1) via the salvage pathway; riboflavin (vitamin B2) and pyridoxine (vitamin B6) and the cofactors: flavin adenine dinucleotide (FAD) and coenzyme A (CoA) that likely provision these nutrients to the host. We propose that bacterial symbionts which are essential to blood-feeding arthropod survival provide attractive targets for the development of novel control methods.

microbiology↗

bioRxiv2020

RNAi gene knockdown in the poultry red mite, Dermanyssus gallinae (De Geer 1778), a tool for functional genomics

BackgroundThe avian haematophagous ectoparasite, Dermanyssus gallinae or the poultry red mite, causes significant economic losses to the egg laying industry worldwide and also represents a significant welfare threat. Current acaricide-based controls are unsustainable due to the mites ability to rapidly develop resistance, thus developing a novel sustainable means of control for D. gallinae is a priority. RNA interference (RNAi) mediated gene silencing is a valuable tool for studying gene function in non-model organisms, but is also emerging as a novel tool for parasite control. MethodsHere we use an in silico approach to identify core RNAi pathway genes in the recently sequenced D. gallinae genome. In addition we utilise an in vitro feeding device to deliver dsRNA to D. gallinae targeting the D. gallinae vATPase subunit A (Dg vATPase A) gene and monitor gene knockdown using quantitive PCR (qPCR). ResultsWe identified core components of the small interfering RNA (siRNA) and micro RNA (miRNA) pathways in D. gallinae, which indicate these gene silencing pathways are likely functional. Strikingly, the Piwi-interacting RNA (piRNA) pathway was absent in D. gallinae. In addition, we demonstrate that feeding Dg vATPase A dsRNA to adult female D. gallinae results in silencing of the targeted gene compared to control mites fed non-specific lacZ dsRNA. In D. gallinae, dsRNA mediated gene knockdown is rapid, detectable 24 hours after oral delivery of dsRNA and persisted for at least 120 hours. ConclusionsThis study has shown the presence of core RNAi machinery components in the D. gallinae genome. In addition, we have developed a robust RNAi methodology for targeting genes in D. gallinae, which will be of value for studying genes of unknown function and validating potential control targets in D. gallinae.

genomics↗

bioRxiv2019

A genomic analysis and transcriptomic atlas of gene expression in Psoroptes ovis reveals feeding- and stage-specific patterns of allergen expression

Psoroptic mange, caused by infestation with the ectoparasitic mite, Psoroptes ovis, is highly contagious, resulting in intense pruritus and represents a major welfare and economic concern for the livestock industry Worldwide. Control relies on injectable endectocides and organophosphate dips, but concerns over residues, environmental contamination, and the development of resistance threaten the sustainability of this approach, highlighting interest in alternative control methods. However, development of vaccines and identification of chemotherapeutic targets is hampered by the lack of P. ovis transcriptomic and genomic resources. Building on the recent publication of the P. ovis draft genome, here we present a genomic analysis and transcriptomic atlas of gene expression in P. ovis revealing feeding- and stage-specific patterns of gene expression, including novel multigene families and allergens. Network-based clustering revealed 14 gene clusters demonstrating either single- or multi-stage specific gene expression patterns, with 3,075 female-specific, 890 male-specific and 112, 217 and 526 transcripts showing larval, protonymph and tritonymph specific-expression, respectively. Detailed analysis of P. ovis allergens revealed stage-specific patterns of allergen gene expression, many of which were also enriched in \"fed\" mites and tritonymphs, highlighting an important feeding-related allergenicity in this developmental stage. Pair-wise analysis of differential expression between life-cycle stages identified patterns of sex-biased gene expression and also identified novel P. ovis multigene families including known allergens and novel genes with high levels of stage-specific expression. The genomic and transcriptomic atlas described here represents a unique resource for the acarid-research community, whilst the OrcAE platform makes this freely available, facilitating further community-led curation of the draft P. ovis genome.

genomics↗