Transcriptome analysis of hemocytes and hepatopancreas in red swamp crayfish, Procambarus clarkii, challenged with white spot syndrome virus

Red swamp crayfish Procambarus clarkii is used for the innate immune defense of crustaceans due to its convenience for laboratory culture and study. To know more about the transcriptome of the crayfish, we constructed and sequenced a cDNA library from a mixture of hemocytes and hepatopancreas from white spot syndrome virus (WSSV)-infected crayfish. By random sequencing, we obtained 9115 high-quality expressed sequence tags with a mean length of 370 bp, representing 3033 unigenes. Most of the unigenes are first reports for the red swamp crayfish. Besides the metabolic genes, many genes that may be involved in the innate immune system of the crayfish are also obtained from the library, such as antimicrobial peptides, pattern recognition receptors, proteases and protease inhibitors, signal transduction proteins, apoptosis-, antioxidant-, and RNA interference-related proteins. We chose ten immune-related genes to analyze their expression pattern by quantitative real time polymerase chain reaction (qRT-PCR) from the hemocytes of normal and WSSV-challenged crayfish. Seven of them, including anti-lipopolysaccharide factor, astacidin, crustin 1, H3 histone family 3A, serine/threonine protein kinase, TGF beta-inducible nuclear protein, and tar RNA binding protein, were upregulated after WSSV injection, but the mRNA expression levels of crustin 2, a lectin, and a digestive cysteine protease decreased after WSSV infection. Our results showed that the transcriptome analysis provides a useful resource for identification of immune related genes and understanding the immune responses of the crayfish.