Microarray of IVM susceptable and resistant Haemonchus contortous

Anthelmintic resistance is a major problem in the global fight against parasitic nematodes., Most previous studies have focused on the analysis of potential candidate genes that may have a role in resistance. Here we take a novel approach in the important parasite, Haemonchus contortus, by investigating changes in microRNA expression between resistant and susceptible parasites. The resistant worms included two geographically distinct strains and two lines generated by multiple rounds of backcrossing between susceptible and resistant parents, with ivermectin selection. All four resistant strains showed increased abundance of a single miRNA, hco-miR-9551, compared to the susceptible strain. hco-miR-9551 is enriched in female worms, is likely to be located on the X chromosome and is found only in clade V parasitic nematodes. Approximately 5-10% of the genomes of the resistant parental strains are introgressed into the respective backcrosses, suggesting that hco-miR-9551, or genes regulated by the miRNA, may be genetically linked to a locus that determines resistance. Genes containing predicted binding sites for hco-miR-9551 were identified computationally and refined based on differential expression in a transcriptomic dataset. These findings advance our conceptual understanding of the molecular mechanisms of anthelmintic resistance in H. contortus and indicate that altered miRNA expression may be linked with drug resistance. All samples were carried out using three biological replicates