Silencing of genes involved in Anaplasma marginale-tick interactions affects the pathogen developmental cycle in Dermacentor variabilis.
BACKGROUND
The 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.


RESULTS
The 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.


CONCLUSIONS
The 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.
Kocan
Katherine M
KM
Department of Veterinary Pathobiology, Center for Veterinary Health Sciences, Oklahoma State University, Stillwater, OK 74078, USA. Katherine.Kocan@okstate.edu
Zivkovic
Zorica
Z
Blouin
Edmour F
EF
Naranjo
Victoria
V
Almazán
Consuelo
C
Mitra
Ruchira
R
de la Fuente
José
J
D042322:Anaplasma marginale / Q000235:genetics* / Q000254:growth & development*; D000818:Animals; D001179:Arthropod Vectors / Q000469:parasitology*; D002417:Cattle; D003870:Dermacentor / Q000469:parasitology*; D020868:Gene Silencing; D005982:Glutathione Transferase / Q000235:genetics; D006790:Host-Parasite Interactions; D008297:Male; D008853:Microscopy; D034622:RNA Interference; D051140:Selenoproteins / Q000235:genetics; D025262:Vacuolar Proton-Translocating ATPases / Q000235:genetics
D051140:Selenoproteins; D005982:Glutathione Transferase; D025262:Vacuolar Proton-Translocating ATPases