Identification of genes differentially expressed in hemocytes of Scylla paramamosain in response to lipopolysaccharide

Although the crab Scylla paramamosain has been cultured in China for a long time, little knowledge is available on how crabs respond to infection by bacteria. A forward suppression subtractive hybridization (SSH) cDNA library was constructed from their hemocytes and the up-regulated genes were identified in order to isolate differentially expressed genes in S. paramamosain in response to bacterial lipopolysaccharide (LPS). A total of 721 clones on the middle scale in the SSH library were sequenced. Among these genes, 271 potentially functional genes were recognized based on the BLAST searches in NCBI and were categorized into seven groups in association with different biological processes using AmiGO against the Gene Ontology database. Of the 271 genes, 269 translatable DNA sequences were predicted to be proteins, and the putative amino acid sequences were searched for conserved domains and proteins using the CD-Search service and BLASTp. Among 271 genes, 179 (66.1%) were annotated to be involved in different biological processes, while 92 genes (33.9%) were classified as an unknown-function gene group. It was noted that only 18 of the 271 genes (6.6%) had previously been reported in other crustaceans and most of the screened genes showed less similarity to known sequences based on BLASTn results, suggesting that 253 genes were found for the first time in S. paramamosain. Furthermore, two up-regulated genes screened from the SSH library were selected for full-length cDNA sequence cloning and in vivo expression study, including Sp-superoxide dismutase (Sp-Cu-ZnSOD) gene and Sp-serpin gene. The differential expression pattern of the two genes during the time course of LPS challenge was analyzed using real-time PCR. We found that both genes were significantly expressed in LPS-challenged crabs in comparison with control. Taken together, the study primarily provides the data of the up-regulated genes associated with different biological processes in S. paramamosain in response to LPS, by which the interesting genes or proteins potentially involved in the innate immune defense of S. paramamosain will be investigated in future.