Abstract
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 +/- A 1 A degrees C) and cold (4 +/- A 1 A degrees C) stresses and compared with control animals (18 +/- A 1 A degrees 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.