Amblyomma maculatum selenoproteins contribute to blood feeding and antioxidant activity

Free radicals are constantly produced in living cells function in signal transduction, pathogen neutralization or simply as a byproduct of normal cellular processes.  The Gulf-Coast tick, Amblyomma maculatum, possesses an elaborate set of antioxidants, including selenoproteins, which circumvent the deleterious effects of oxidative stress.  The selenocysteine residue is incorporated cotranslationally in a process that requires a number of factors to recode the UGA stop.  In the current work, we have examined the role of selenoproteins in tick feeding by targeting the gene encoding the selenocysteine-specific elongation factor for transcriptional disruption via RNA interference.  Ticks injected with sef-dsRNA had a lower engorged weight, compared to control, indicating that selenoproteins contribute to the tick feeding.  No significant differences in oviposit were noted between sef-dsRNA injected and control ticks.  Surprisingly, antioxidant activity in saliva was undetectable in the sef-dsRNA knockdowns, despite the fact that ticks possess a strong compensatory mechanism for transcriptional activation of other antioxidant genes.  These data indicate that selenoproteins are important salivary antioxidant constituents but are not essential for tick survival or reproduction.