pubmed.ncbi.nlm.nih.gov

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

. 2014 Aug;23(4):497-510.

doi: 10.1111/imb.12098. Epub 2014 Apr 4.

Affiliations

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

S Adamson et al. Insect Mol Biol. 2014 Aug.

Abstract

The Gulf-Coast tick, Amblyomma maculatum, possesses an elaborate set of selenoproteins, which prevent the deleterious effects from oxidative stress that would otherwise 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 did not vary significantly in salivary glands or midguts throughout the bloodmeal. However, there was 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 with controls, which is probably the result of compensatory transcriptional expression of genes involved in combating reactive oxygen species. In fact, quantitative real-time PCR data suggest that the transcriptional expression of catalase increased in ticks injected with selM-double-stranded RNA. Additionally, the transcriptional expression of selN decreased ∼90% in both SelK/SelM knockdowns. These data indicate that SelK and SelM are salivary antioxidants but are not essential for tick survival or reproduction and are compensated by other antioxidant systems.

Keywords: oxidative stress; selenoprotein K; selenoprotein M; tick antioxidants.

© 2014 The Royal Entomological Society.

PubMed Disclaimer

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1
Figure 1

The multiple sequence alignment of Selenoprotein K. The selenocysteine residue (U) is highlighted in black.

Figure 2
Figure 2

The multiple sequence alignment of Selenoprotein M. The selenocysteine residue (U) is highlighted in black. Selenoprotein M is predicted to have a signal peptide (highlighted dark grey), targeting the protein for secretion.

Figure 3
Figure 3

The evolutionary history of Selenoprotein K was inferred using the Maximum Parsimony method. The percentage of replicate trees in which the associated taxa clustered together in the bootstrap test (1000 replicates) is shown next to the branches. Tick sequences are indicated in bold and sequences denoted with asterisks are derived from species which lack the capacity to synthesize selenoproteins and represent cysteine-containing homologs. Scale bar represents amino acid substitutions per position.

Figure 4
Figure 4

The evolutionary history of Selenoprotein M was inferred using the Maximum Parsimony method. The percentage of replicate trees in which the associated taxa clustered together in the bootstrap test (1000 replicates) is shown next to the branches. Tick sequences are indicated in bold and sequences denoted with asterisks are derived from species which lack the capacity to synthesize selenoproteins and represent cysteine-containing homologs. Scale bar represents amino acid substitutions per position.

Figure 5
Figure 5

The transcriptional gene expression of selK and selM in the salivary glands (top) and midguts (bottom) of female A. maculatum ticks throughout the blood meal. The gene expression of SelK and SelM was normalized to the unfed developmental stage using β-Actin as a reference gene.

Figure 6
Figure 6

Quantitative PCR showing transcriptional expression of SelK and SelM in A. maculatum salivary glands of control and SelM- or SelK-dsRNA and GFP-dsRNA (control) injected ticks. Samples were obtained seven days post-infestation. Expression was normalized against the β-Actin. Asterisks indicate a significant difference compared to control (**p≤0.001).

Figure 7
Figure 7

Photographs of the oviposition of ticks injected with selenoprotein-dsRNA or control ticks.

Figure 8
Figure 8

The relative total antioxidant capacity was determined in extracts of tick tissues (top) and in pooled saliva collected from ticks injected with selenoprotein-dsRNA compared to control (GFP-dsRNA) (bottom) collected from tissue seven days post-infestation. Asterisks indicate a significant difference compared to control (**p≤0.001). The total antioxidant capacity within saliva of unfed ticks was not determined due to difficulties in collecting sufficient saliva to perform experimentation.

Figure 9
Figure 9

The compensatory effect on selenoprotein transcriptional expression in A. maculatum salivary glands injected with SelK- or SelM-dsRNA. Asterisks indicate a statistically significant difference compared to control (GFP-dsRNA injected) (*p<0.05).

Similar articles

Cited by

References

    1. Adamsom SW, Browning RE, Budachetri K, Ribeiro JM, Karim S. Knockdown of Selenocysteine-Specific Elongation Factor in Amblyomma maculatum alters the pathogen burden of Rickettsia parkeri with epigenetic control by the Sin3 Histone Deacetylase Corepressor Complex. PLoS One. 2013;8:e82012. - PMC - PubMed
    1. Adamson SW, Browning RE, Chao CC, Bateman RC, Jr, Ching WM, Karim S. Molecular characterization of tick salivary gland glutaminyl cyclase. Insect Biochem Mol Biol. 2013;43:781–793. - PMC - PubMed
    1. Altschul SF, Gish W, Miller W, Myers EW, Lipman DJ. Basic local alignment search tool. J Mol Biol. 1990;215:403–10. - PubMed
    1. Anand SB, Murugan V, Prabhu PR, Anandharaman V, Reddy MV, Kaliraj P. Comparison of immunogenicity, protective efficacy of single and cocktail DNA vaccine of Brugia malayi abundant larval transcript (ALT-2) and thioredoxin peroxidase (TPX) in mice. Acta Trop. 2008;107:106–12. - PubMed
    1. Anisuzzaman, Islam MK, Alim MA, Miyoshi T, Hatta T, Yamaji K, Matsumoto Y, Fujisaki K, Tsuji N. Longistatin is an unconventional serine protease and induces protective immunity against tick infestation. Mol Biochem Parasitol. 2012;182:45–53. - PubMed

Publication types

MeSH terms

Substances

LinkOut - more resources