Macrophage migration inhibitory factor expression and protein localization in <Emphasis Type="Italic">Amblyomma americanum</Emphasis> (Ixodidae) |
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Authors: | C J Bowen D C Jaworski N B Wasala L B Coons |
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Institution: | (1) Department of Entomology and Plant Pathology, Oklahoma State University, 127 Noble Research Center, Stillwater, OK 74078-8031, USA;(2) Integrated Microscopy Center, The University of Memphis, 201 Life Sciences Bldg, 3774 Walker, Memphis, TN 38152-3560, USA; |
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Abstract: | Amblyomma americanum (L.) ticks continue to emerge as disease vectors in many areas of the United States. Tick macrophage migration inhibitory
factor (MIF) was first identified in A. americanum females and has been demonstrated to inhibit macrophage movement to the same extent as human MIF. This study was conducted
to further characterize and elucidate the physiological role for MIF in tick feeding. A relative quantitative PCR assay was
developed to determine the level of MIF gene expression during tick feeding. In addition, RNAi techniques were used to silence
MIF prior to blood feeding. Physiological parameters of tick engorgement weight, length of feeding interval, and egg masses
were observed to check for phenotypic manifestations of RNA silencing. Specific tick MIF antibody was used to localize MIF
protein in frozen tick tissue sections. Tissue specific gene expression indicated that the midgut tissues were the most highly
enriched for the MIF. Levels of gene expression did not parallel MIF protein pools seen in tissue sections. Of particular
importance was the finding that unfed tick salivary glands appear to contain vesicles that are specific for MIF protein. This
is the first demonstration of a pool of MIF that could be secreted during the first hours of tick feeding. While MIF silencing
was demonstrated at the molecular level, no physiological phenotype was apparent. The MIF protein pools already available
in the tissues may be sufficient to accomplish female tick feeding. Our studies show that the most prominent source of MIF
during tick feeding is the midgut tissue. Future studies will address the role of MIF in blood feeding and nutrient digestion
in the immature life stages of the tick. |
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