De novo transcriptome sequencing and differential gene expression analysis of two parasitic human Demodex species

Demodex are among the tiniest organisms in Acari and are important mammalian parasites. However, differences in pathogenicity between two human parasites, Demodex folliculorum and Demodex brevis, remain unknown. Related genetic studies are limited by RNA extraction difficulties and molecular data deficiencies. In this study, RNA extraction, de novo sequencing, functional annotation, and differential gene expression analyses were performed to compare D. folliculorum and D. brevis. This yielded 67.09 and 65.10 million clean reads, respectively, with similar annotations. Bioinformatics analyses and manual alignments identified 237 coding sequences comprising 48 genes from 29 families, including five important functional classes. Of these, 30 genes from 20 families related to metabolism, motion, detoxification and stress response, and allergic reaction were differentially expressed between the two species. Cathepsin type 1, serine protease inhibitor, arginine kinase, triosephosphate isomerase, muscle-specific protein 20-2, myosin alkaline light chain, troponin C, tropomyosin, and heat shock protein 90 were highly expressed in D. folliculorum, whereas cathepsin type 2, aspartic protease, serine protease, myosin heavy chain type 2, and alpha tubulin type 1C were highly expressed in D. brevis. Verified coding sequences were nearly consistent with unigene clusters. Further, absolute quantification results demonstrated that differentially expressed genes followed the predicted expression trend. Therefore, the first RNA sequencing and functional annotation analysis of two Demodex species was successful. Differential expression of important functional genes is likely implicated in pathogenicity disparities between these two species. Our study provides molecular data and technical support for further studies on human Demodex pathogenicity and functional genes.