| Summary: | Epigenetic mechanisms have not been characterized in ticks despite their importance as vectors of human and animal diseases worldwide. Our investigation identifies and functionally characterizes the orthologue of S-adenosylmethionine (SAM) binding methyltransferase enzyme, disruptor of telomeric silencing 1-like (DOT1L) in <i>Ornithodoros moubata</i> (OmDOT1L), a soft tick vector for the relapsing fever pathogen <i>Borrelia duttonii</i> and the African swine fever virus. The OmDOT1L tertiary structure was predicted and compared to the <i>Homo sapiens</i> DOT1L which had been co-crystalized with SGC0946, a DOT1L-specific inhibitor. The amino acid residues crucial for SAM and SGC0946 binding conserved in most DOT1L sequences available, are also conserved in OmDOT1L. Quantitative PCR of <i>Omdot1l</i> during <i>O. moubata</i> life stages showed that transcripts were significantly upregulated in first-stage nymphs. <i>O. moubata</i> larvae exposed to SGC0946 displayed high mortality during molting to first-stage nymphs. Furthermore, a significant decrease in weight was observed in second-stage nymphs fed on recombinant OmDOT1L-immunized rabbits. In contrast, artificial blood feeding supplemented with SGC0946 did not affect survival and reproductive performance of adult female ticks. We concluded that OmDOT1L plays an essential role in the regulation of larval molting and the feeding of <i>O. moubata</i> second-stage nymphs.
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