De novo transcriptome sequencing and functional annotation of Demodex canis

Demodex canis is an important parasitic mite causing skin lesions in dogs. However, molecular studies on this species are limited because of the lack of transcriptomic data. To obtain functional genes of D. canis, mites were collected and RNA was extracted for transcriptome sequencing and functional annotation. Coding sequences (CDSs) of important functional genes were screened and identified using bioinformatics strategies. Six complete CDSs were amplified by specific primers, cloned and sequenced. Results demonstrated that the quantity of the RNA extracted from 100 mites was 12.8 ng and the RNA integrity number was 5.4, indicating that it could be used to construct a cDNA library. Transcriptome sequencing yielded 263,619 unigenes, of which 151,048 (57.3%) were functionally annotated. Using bioinformatics strategies, 58 total CDSs were identified as homologous to those of closely related mite species, including 16 types of allergen genes, 13 types of protease genes, and nine types of motion-related genes. The verified CDSs were almost identical to the CDSs of unigenes. Phylogenetic analyses of tropomyosin further revealed that the verified CDSs clustered successively with those of Demodex species and Tetranychus species in Raphignathae, which agreed with the morphological classification, demonstrating the reliability of the transcriptomic data. In conclusion, this study is the first to successfully sequence transcriptome of D. canis, perform functional annotation, and verify CDSs, which will provide ample data for further studies on the functional genes and molecular pathogenic mechanism of D. canis.