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Title: Global transcriptional analysis reveals surface remodeling of anaplasma marginale in the tick vector

item HAMMAC, KENITRA - Washington State University
item AGUILAR PIERLÉ, SEBASTIÁN - Washington State University
item CHENG, XIAOYA - Washington State University
item Scoles, Glen
item BRAYTON, KELLY - Washington State University

Submitted to: Parasites & Vectors
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/8/2014
Publication Date: 4/21/2014
Citation: Hammac, K.G., Aguilar Pierlé, S., Cheng, X., Scoles, G.A., Brayton, K.A. 2014. Global transcriptional analysis reveals surface remodeling of anaplasma marginale in the tick vector. Parasites & Vectors. 7:193.

Interpretive Summary: Bovine anaplasmosis is caused by the tick-borne bacterial pathogen Anaplasma marginale. Anaplasmosis is globally distributed and can lead to significant morbidity and mortality among cattle. In order to be transmitted this pathogen must be able to survive in both its tick vector and its mammalian host. Understanding the differences in protein genes expressed between these two different environmental conditions may provide strategies for interfering with transmission, especially if potential vaccine candidates can be identified and exploited. In this work we have studied differences in protein gene expression in the blood of the infected bovine host and in infected tick cell culture as a model for the tick vector. We have identified differentially transcribed genes in fourteen different pathways or component groups and one of the most significantly altered groups was surface exposed proteins, suggesting that the proteins expressed on the surface of the bacterium are altered during the transition from bovine host to tick vector. This work confirms that tick cell culture is a useful model for studying A. marginale gene expression in tick infection and may provide information leading to vaccine targets for transmission blocking vaccination strategies.

Technical Abstract: Background: Pathogens dependent upon vectors for transmission to new hosts undergo environment specific changes in gene transcription dependent on whether they are replicating in the vector or the mammalian host. Differential gene transcription, especially of potential vaccine candidates, is of interest in Anaplasma marginale, the tick-borne causative agent of bovine anaplasmosis. Methods: RNA-seq technology allowed a comprehensive analysis of the transcriptional status of A. marginale genes in two conditions: bovine host blood and tick derived cell culture, a model for the tick vector. Quantitative PCR was used to assess transcription of a set of genes in A. marginale infected tick midguts and salivary glands at two time points during the transmission cycle. Results: Genes belonging to fourteen pathways or component groups were found to be differentially transcribed in A. marginale in the bovine host versus the tick vector. One of the most significantly altered groups was composed of surface proteins. Of the 56 genes included in the surface protein group, eight were up regulated and 26 were down regulated. The down regulated surface protein encoding genes include several that are well studied due to their immunogenicity and function. Quantitative PCR of a set of genes demonstrated that transcription in tick cell culture most closely approximates transcription in salivary glands of recently infected ticks. Conclusions: The ISE6 tick cell culture line is an acceptable model for early infection in tick salivary glands, and reveals disproportionate down regulation of surface protein genes in the tick. Transcriptional profiling in other cell lines may help us simulate additional microenvironments. Understanding vector-specific alteration of gene transcription, especially of surface protein encoding genes, may aid in the development of vaccines or transmission blocking therapies.