Functional annotation and analysis of the hard tick Dermacentor nuttalli midgut genes

Ticks are hematophagous vectors that transmit a variety of pathogens, posing significant threats to the health of both humans and animals. Tick midgut proteins play essential roles in blood digestion, feeding, toxic waste processing, and pathogen transmission. Dermacentor nuttalli is the primary vector of tick-borne pathogens, including rickettsioses in the Qinghai-Tibet Plateau. However, there is a lack of genomic, transcriptomic, and proteomic information regarding the biology of D. nuttalli. In this study, we assembled and compared the midgut transcriptomes of female D. nuttalli ticks at 0, 24, 48, 72, and 96 h during blood feeding, identifying the genes with differentially regulated expression following feeding. The obtained data were compiled and annotated in multiple databases including Nr, NT, PFAM, KOG, KEGG, and GO. The high-quality clean readings of midgut tissue at the different blood-feeding times were recorded as 22,524,912, 23,752,325, 20,377,718, 21,300,710, and 20,378,658, respectively. The transcripts were classified into eight large categories, including immunogenic proteases (8.37%), protease inhibitors (0.85%), transporters (3.96%), ligand binding proteins (1.98%), ribosomal function proteins (0.94%), heat shock proteins (0.30%), other proteases and miscellaneous proteins (57.61%), and unknown proteins (26.00%). Significant differences were observed in the genes obtained at 0, 24, 48, 72, and 96 h during blood feeding. The differentially expressed genes include catalytic proteins that play an important role in accelerating biochemical reactions, binding activity proteins which are involved in various molecular interactions, and proteins that actively participate in multiple metabolic pathways and cellular processes. Notably, the gene expression in the midgut of D. nuttalli shows dynamic changes every 24 h throughout the blood-feeding process. This change may represent an equivalent strategy of antigenic variation for ticks, designed to protect their essential feeding function against the host's immune system. The tick antigens identified in this study may serve as promising candidates for the development of effective vaccines or as drug targets for acaricides.