Oligo-microarray analysis and identification of stress-immune response genes from manila clam (Ruditapes philippinarum) exposure to heat and cold stresses.

Thermal stress regulates the complex system of gene expression and downstream biochemical and physiological responses in aquatic species. To identify genes involved in heat stress responses in manila clam (Ruditapes philippinarum), microarray analysis was conducted using clam transcriptome generated by pyrosequencing of cDNA library. Manila clams were exposed to heat (30 ± 1 °C) and cold (4 ± 1 °C) stresses and compared with control animals (18 ± 1 °C). Heat stressed animals have changed greater number of transcripts (8,306) than cold stress (7,573). Results of both heat and cold exposure has shown that over 2-fold up-regulated or down regulated (>2-or <2-fold) transcripts were higher at 24 h than at 6 h. It suggests that silent and constitutive express genes can activate at critical stage of thermal stress which could be between 6 and 24 h post stresses. We identified wide range of stress-immune response genes such as transcription factors, heat shock proteins, antioxidant and detoxification enzymes, inflammatory and apoptosis related genes, cell adhesion molecules, cytokines, and IFN regulatory proteins. Histological results revealed that non-specific cellular alterations such as lesions, hypertrophy, and necrosis in stressed gills could be due to decrease of gas exchange rate which may cause hypoxia.

Two molluscan BCL-2 family members from Manila clam, Ruditapes philippinarum: molecular characterization and immune responses.

Apoptosis based immune responses are important component of host defense in mollusks. In this study, we have identified two novel molluscan BCL-2 cDNAs from Manila clam, Ruditapes philippinarum and named as RpBCL-2A and RpBCL-2B. There were four and three highly conserved BCL-2 homology (BH) regions in RpBCL-2A and RpBCL-2B, respectively suggesting these two genes could be different isoforms of anti-apoptotic BCL-2 family. Phylogenetic results revealed that Manila clam BCL-2 genes were clustered closely with invertebrate BCL-2 members. It gives evidence of their common origin and conserved features of invertebrate BCL-2 family. RpBCL-2A and 2B were expressed in tissue-specific manner showing the highest and lowest level of expression in gills and hemocytes, respectively. However there was no clear expression profile difference between two genes. After Vibrio tapetis challenge, transcriptional responses of RpBCL-2A and RpBCL-2B were induced in gills and hemocytes with high variation that could be due to effects of immune reactions of other host defense molecules.