Identification of genes that are differentially expressed in hemocytes of the Pacific blue shrimp (Litopenaeus stylirostris) surviving an infection with Vibrio penaeicida

Considerable progress has been made in the field of invertebrate immunity through the characterization of genes involved in the response to infection and/or stress. However, the mechanisms by which commercially important marine invertebrates can successfully survive an infection remain largely unknown. For the first time in an invertebrate model, we have searched to discover genes involved in the survival capacity of shrimp using the highly pathogenic bacteria, Vibrio penaeicida. In the present study, we applied the technique of suppression subtractive hybridization (SSH) to hemocyte cDNAs from infected and uninfected shrimp, only using samples from individuals that had survived 96 h postinfection. The resulting library contains 260 expressed sequence tagged ( EST) cDNA clones potentially representing highly expressed genes in surviving shrimp. Sequence similarity comparisons were made, and putative identities were assigned to clones that were at least 51% identical to known genes. This analysis showed two functional categories that were highly represented: those of genes involved in immune reactions (10.7% of the ESTs) and those involved in proliferation-hematopoiesis (10.3%). Expression pattern profile analyses of selected ESTs at different times postinfection confirmed the differential expression of the genes and efficiency of the SSH method. Differences in gene transcript abundance, for select ESTs encoding antimicrobial effectors, were evidenced by real-time PCR between shrimp that survived acute Vibrio infection and those individuals that did not survive acute Vibrio infection. These results suggest there are basic differences at the level of transcript abundance for genes directly involved in immune and hematopoietic processes from shrimp that survive and do not survive infection.