Profiling the proteome of salivary glands and ovaries of the tick Ixodes ricinus

Purpose: Hard ticks are hematophagous arthropods vectors that transmit important human and animal pathogens. Ixodes ricinus is one of the most important tick species in Europe, able to transmit, among others, the bacterium agent of Lyme disease. The goal of this study was to establish a method to characterize the proteome of I. ricinus, as a basis for future studies on the interaction with pathogens proteins during the phase of their lifecycle in the tick. To this purpose, the protein profile of the ovary (OV) and the salivary glands (SG) were generated. Experimental description: 40 Semi-engorged I. ricinus ticks, collected from roe-deer (Capreolus capreolus) were manually dissected under a stereomicroscope to collect salivary glands and ovaries. Tissues were pooled and mechanically disrupted, sonicated and DNA and proteins extracted. Proteins were separated by 2-DE on 7 cm IPG strips, with nonlinear (NL) pH 3–10 gradient followed by 12.5% SDS-PAGE on 8x6 cm slabs. Identification of proteins was achieved by submitting to LC-MS/MS the peptide mixture generated upon tryptic digestion of the material carefully extracted from gel spots. Results: The mean spot number in Coomassie stained gels was 235±29 in SG and 221±21 in OV (Figure 1, panels A and B). Comparison of 2-DE patterns for SG and OV (by means of PD Quest version 8.1 software) revealed several qualitative and quantitative differences between the two sets of pools, some protein spots present in SG profile being absent from the OV one and viceversa. Among the 21 spots showing significant differences in the relative abundance between the two pools of samples, eight showed 4- to 18-fold increase/decrease in density. These spots were excised from the gel, de-stained, digested with trypsin, and peptides were submitted to LC-MS/MS.