Constructing and detecting a cDNA library for mites.

RNA extraction and construction of complementary DNA (cDNA) library for mites have been quite challenging due to difficulties in acquiring tiny living mites and breaking their hard chitin. The present study is to explore a better method to construct cDNA library for mites that will lay the foundation on transcriptome and molecular pathogenesis research. We selected Psoroptes cuniculi as an experimental subject and took the following steps to construct and verify cDNA library. First, we combined liquid nitrogen grinding with TRIzol for total RNA extraction. Then, switching mechanism at 5' end of the RNA transcript (SMART) technique was used to construct full-length cDNA library. To evaluate the quality of cDNA library, the library titer and recombination rate were calculated. The reliability of cDNA library was detected by sequencing and analyzing positive clones and genes amplified by specific primers. The results showed that the RNA concentration was 836 ng/μl and the absorbance ratio at 260/280 nm was 1.82. The library titer was 5.31 × 10(5) plaque-forming unit (PFU)/ml and the recombination rate was 98.21%, indicating that the library was of good quality. In the 33 expressed sequence tags (ESTs) of P. cuniculi, two clones of 1656 and 1658 bp were almost identical with only three variable sites detected, which had an identity of 99.63% with that of Psoroptes ovis, indicating that the cDNA library was reliable. Further detection by specific primers demonstrated that the 553-bp Pso c II gene sequences of P. cuniculi had an identity of 98.56% with those of P. ovis, confirming that the cDNA library was not only reliable but also feasible.