Abstract
Heavy tick burden on beef cattle account for huge economic losses globally, with an estimated value of US$22-30 billion per annum. In Australia, ticks cost the northern beef industry approximately A$170-200 million. Methods to evaluate and predict tick resistance would therefore be of great value to the global cattle trade. Exosomes (EX) are small extracellular vesicles (EVs) of ~30-150nm diameter and have gained popularity for their diagnostic and prognostic potential. EX contain, among other biomolecules, various types of RNA including micro-RNA (miRNA) and long noncoding RNA (lncRNA). MiRNA specifically have been validated as therapeutic biomarkers as they perform regulatory functions at the post-transcriptional level and are differentially expressed between divergent groups. The objective of the present study was to evaluate the miRNA profiles of EV and fractionated exosomal samples of high and low tick-resistant beef cattle to highlight potential miRNA biomarkers of tick resistance. Cows (n = 3/group) were classified into high or low tick resistant groups according to a novel scoring system. EVs and EX were isolated and fractionated from the blood plasma of high and low tick resistant cattle using established isolation and enrichment protocols. The resultant EX and non-EX samples were processed for next generation miRNA sequencing. Offspring of the cows in each high and low tick resistant group underwent the same processing for blood plasma EX, non-EX and miRNA analysis to evaluate the heritability of miRNA associated with tick resistance. A total of 2631 miRNAs were identified in EX and non-EX fractionated samples from high and low tick-resistant beef cattle. MiR-449a was highly expressed in maternal high tick-resistant EX samples. Of these, 174 were novel miRNAs, and 10 were differentially expressed (DE) (FDR < 0.05). These 10 DE miRNAs were also present in EVs, and three miRNAs were highly expressed: miR-2419-3p, miR-7861-3p and miR-2372-5p. Although 196 novel miRNAs were identified in fractionated samples of offspring, no miRNA were differentially expressed in these animals.
Highlights
Ticks pose a considerable threat to livestock globally, in beef cattle farming
All the samples yielded more than 100pg (0.1 ng) of miRNA according to quality control testing (Table 2)
3.3.1 Size Exclusion Chromatography (SEC) (EX and Non-EX) miRNA Profiles- Mother/ Sire – High vs. Low Tick Resistant 2632 miRNAs were identified in high and low tick resistant cattle. 2458 miRNAs were identified in miRbase database, and 174 novel miRNAs were identified by miRDeep2
Summary
Ticks pose a considerable threat to livestock globally, in beef cattle farming. In Australia, the tick burden costs the northern beef industry around A$170-200 million (Playford et al, 2005). Tick infestation causes stress and weakens the immune system, which affects the performance of the beef cow (Mapholi et al, 2014). Farm management systems use conventional options such as acaricides to control tick infestation, this is not a sustainable strategy in the long term (Mapholi et al, 2014). Lack of understanding on the whole genome of parasites and antigenic variation challenge sustainable use of parasite vaccines against ticks (Barré et al, 2011; Lew-Tabor and Rodriguez Valle, 2016). Farmers utilize different grazing management techniques such as pasture rotation and pasture burning to reduce exposure and control tick populations (Kasaija et al, 2021). Cattle-ticks represent a top priority endemic disease for the red meat industry in Australia (Lane et al, 2015)
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