Abstract
BackgroundThe cattle pathogen, Anaplasma marginale, undergoes a developmental cycle in ticks that begins in gut cells. Transmission to cattle occurs from salivary glands during a second tick feeding. At each site of development two forms of A. marginale (reticulated and dense) occur within a parasitophorous vacuole in the host cell cytoplasm. However, the role of tick genes in pathogen development is unknown. Four genes, found in previous studies to be differentially expressed in Dermacentor variabilis ticks in response to infection with A. marginale, were silenced by RNA interference (RNAi) to determine the effect of silencing on the A. marginale developmental cycle. These four genes encoded for putative glutathione S-transferase (GST), salivary selenoprotein M (SelM), H+ transporting lysosomal vacuolar proton pump (vATPase) and subolesin.ResultsThe impact of gene knockdown on A. marginale tick infections, both after acquiring infection and after a second transmission feeding, was determined and studied by light microscopy. Silencing of these genes had a different impact on A. marginale development in different tick tissues by affecting infection levels, the densities of colonies containing reticulated or dense forms and tissue morphology. Salivary gland infections were not seen in any of the gene-silenced ticks, raising the question of whether these ticks were able to transmit the pathogen.ConclusionThe results of this RNAi and light microscopic analyses of tick tissues infected with A. marginale after the silencing of genes functionally important for pathogen development suggest a role for these molecules during pathogen life cycle in ticks.
Highlights
The cattle pathogen, Anaplasma marginale, undergoes a developmental cycle in ticks that begins in gut cells
The results demonstrated that gene knockdown reduced the number of reticulated (vegetative) form (RF)- and dense form (DF)-containing colonies in various tick tissues with implications for pathogen replication, development and transmission in ticks, and suggested that these genes may be good targets for development of a new generation of pathogen transmission-blocking vaccines for control of bovine anaplasmosis directed toward reducing exposure of vertebrate hosts to A. marginale
Confirmation of RNA interference (RNAi) of tick genes and A. marginale infection levels in ticks The effect of RNAi on glutathione S-transferase (GST), selenoprotein M (SelM) and subolesin gene silencing was confirmed in ticks after acquisition feeding (AF) and transmission feeding (TF) (Table 1)
Summary
The cattle pathogen, Anaplasma marginale, undergoes a developmental cycle in ticks that begins in gut cells. Found in previous studies to be differentially expressed in Dermacentor variabilis ticks in response to infection with A. marginale, were silenced by RNA interference (RNAi) to determine the effect of silencing on the A. marginale developmental cycle. These four genes encoded for putative glutathione S-transferase (GST), salivary selenoprotein M (SelM), H+ transporting lysosomal vacuolar proton pump (vATPase) and subolesin. Ticks transmit pathogens that impact both human and animal health [1] Of these tick-borne pathogens, those belonging to the genus Anaplasma (Rickettsiales: Anaplasmataceae) are obligate intracellular organisms found exclusively within parasitophorous vacuoles in the cytoplasm of both vertebrate and tick host cells [2]. Gut muscle and fat body cells may become infected with A. marginale during tick feeding
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