Differential Expression of Putative Ornithodoros turicata Defensins Mediated by Tick Feeding

Abstract

Additional research on soft ticks in the family Argasidae is needed to bridge the knowledge gap relative to hard ticks of the family Ixodidae; especially, the molecular mechanisms of Ornithodoros biology. Ornithodoros species are vectors of human and animal pathogens that include tick-borne relapsing fever spirochetes and African swine fever virus. Soft tick vector-pathogen interactions involving components of the tick immune response are not understood. Ticks utilize a basic innate immune system consisting of recognition factors and cellular and humoral responses to produce antimicrobial peptides, like defensins. In the present study, we identified and characterized the first putative defensins of Ornithodoros turicata, an argasid tick found primarily in the southwestern United States and regions of Latin America. Four genes (otdA, otdB, otdC, and otdD) were identified through sequencing and their predicted amino acid sequences contained motifs characteristic of arthropod defensins. A phylogenetic analysis grouped these four genes with arthropod defensins, and computational structural analyses further supported the identification. Since pathogens transmitted by O. turicata colonize both the midgut and salivary glands, expression patterns of the putative defensins were determined in these tissues 1 week post engorgement and after molting. Defensin genes up-regulated in the tick midgut 1 week post blood feeding were otdA and otdC, while otdD was up-regulated in the midgut of post-molt ticks. Moreover, otdB and otdD were also up-regulated in the salivary glands of flat post-molt ticks, while otdC was up-regulated within 1 week post blood-feeding. This work is foundational toward additional studies to determine mechanisms of vector competence and pathogen transmission from O. turicata.

Defensins as a promising class of tick antimicrobial peptides: a scoping review

“…Many stimuli related to microbial invasions, such as injury, infection, and blood-feeding, induce the secretion of these protective substances. Defensins were also observed to be up-regulated after molting [ 27 ]. A range of tissues in ticks, such as midgut, hemolymph, salivary glands, ovary, and fat body, express defensins, while the distribution of defensins appears to be either tissue-specific or ubiquitous [ 26 ].…”

Identification of the Gene Repertoire of the IMD Pathway and Expression of Antimicrobial Peptide Genes in Several Tissues and Hemolymph of the Cockroach Blattella germanica

“…As compared to Drosophila , where some production of AMPs takes place in the midgut [ 17 ], our results demonstrate that in B. germanica , the majority of AMP production in the digestive system is detected in the salivary glands. Similarly, high expression of an AMP gene has also been observed in the salivary glands and midgut of Bemisia tabaci (Gennadius) [ 43 ], and some defensin genes are expressed in both salivary glands and midgut, and others are specific to one of these tissues in the tick Ornithodoros turicata (Dugès) [ 44 ]. In insects, as a general rule, AMP gene expression is silent in the absence of an immune challenge [ 45 ], although RNAseq or qRT-PCR methodologies can detect miniscule levels of gene expression.…”

Detection of African Swine Fever Virus in Ornithodoros Tick Species Associated with Indigenous and Extralimital Warthog Populations in South Africa

“…Several African and exotic Ornithodoros species have been found capable of sustaining replication and transmission of ASFV experimentally, but vector competence appears to be regulated by multiple tick species- and virus strain-specific factors [ 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 , 61 , 62 , 63 , 64 , 65 , 66 , 67 , 68 , 69 , 70 , 71 , 72 , 73 ]. Hence, it is important that both ticks and viruses should be identified accurately in assessing and recording vector potential.…”