Transcriptional activation of antioxidants may compensate for selenoprotein deficiencies in Amblyomma maculatum (Acari: Ixodidae) injected with selK‐ or selM‐dsRNA

Abstract

The Gulf-Coast tick, Amblyomma maculatum, possesses an elaborate set of selenoprotein, which prevent the deleterious effects from oxidative stress that occur during feeding. In the current work, we examined the role of Selenoprotein K (SelK) and Selenoprotein M (SelM) in feeding A. maculatum by bioinformatics, transcriptional gene expression, RNA interference and antioxidant assays. The transcriptional expression of SelK does not vary significantly in salivary glands or midguts throughout the blood meal. However, there is a 58-fold increase in transcript levels of SelM in tick midguts. Ticks injected with selK-dsRNA or selM-dsRNA did not reveal any observable differences in egg viability but oviposition was reduced. Surprisingly, salivary antioxidant activity was higher in selenoprotein knockouts compared to controls, which is likely due to compensatory transcriptional expression of genes involved in combating reactive oxygen species. In fact, RT-qPCR data suggest the transcriptional expression of catalase increased in ticks injected with selM-dsRNA. Additionally, the transcriptional expression of selN decreased ~90% in both SelK/SelM knockdowns.

An insight into the functional role of thioredoxin reductase, a selenoprotein, in maintaining normal native microbiota in the Gulf Coast tick (Amblyomma maculatum)

“…Because most central antioxidant enzyme reactions can be catalyzed by at least one or more proteins of the antioxidant defense network, inhibition of a single target antioxidant protein is unlikely to be efficient at impairing tick feeding (Table 2) through induction of oxidative stress. The normal tick phenotype (i.e., tick attachment duration, weight gain/loss, fecundity and vitellogenesis) in TrxR-deficient ticks was not impacted, as has been shown in our previous studies (Adamson et al 2014; Adamson et al 2013). …”

“…The Sec-encoded motif is found at the C-terminus in I. scapularis , A. maculatum and R. norvegicus whereas cysteine residues are present in other species, A. gambiae and D. melanogaster (Fig. 1), and has been described in other tick selenoproteins, specifically SelK and SelM (Adamson et al 2014). At the C-terminus the Gly-Cys-Sec-Gly motif is essential for catalytic activity of enzyme thioredoxin reductase as determined by mutational analysis, and compared to the C-terminus of glutathione reductase, the presence of selenocysteine is the only change (Zhong and Holmgren 2000).…”

“…The sialotranscriptome of this tick reveals the presence of various antioxidants and selenoproteins including TrxR, which is a major contributor to the tick antioxidant system (Karim et al 2011). Tick selenoproteins have been shown to play important roles in mitigating oxidative stress and pathogen colonization (Adamson et al 2014; Adamson et al 2013). The functional role of TrxR has been implicated in various metabolic pathways including control of organismal growth, immune functions, and anti-apoptosis via the thioredoxin-thioredoxin reductase system (Muller 1991; Salz et al 1994; Yodoi and Uchiyama 1992).…”

RNA Interference – A Powerful Functional Analysis Tool for Studying Tick Biology and its Control

“…In contrast, a study on A. maculatum showed that silencing two selenoproteins did not alter blood feeding, although the egg output was reduced. Interestingly, the total antioxidant capacities of the saliva from knockdowned ticks were higher, indicating that other antioxidant enzymes may have compensated for the absence of selenoproteins [138]. In another study, silencing thioredoxin reductase, another selenoprotein, in A. maculatum did not have a negative impact on blood feeding and reproduction.…”

Amblyomma maculatum SECIS binding protein 2 and putative selenoprotein P are indispensable for pathogen replication and tick fecundity

“…Therefore, to successfully feed and survive, ticks must somehow prevent the detrimental and promote the beneficial aspects of ROS release, which suggests that precise regulatory strategies must exist for maintaining appropriate ROS levels both within the tick and possibly at the tick—host interface. Our previous studies have revealed an adaptive co-evolutionary process that enables the survival of the tick-borne pathogen Rickettsia parkeri by manipulating an antioxidant defense system associated with selenium, which includes a full set of selenoproteins and other antioxidants (Adamson et al, 2014, 2013; Budachetri et al, 2017; Budachetri and Karim, 2015; Crispell et al, 2016; Karim et al, 2011; Karim and Ribeiro, 2015; Kumar et al, 2016). ROS generation is one of the first lines of host defense against invading microbes (Ha et al, 2005).…”