Gene expression study in Bathymodiolus azoricus populations from three North Atlantic hydrothermal vent sites.

The deep-sea hydrothermal vents are known as harsh environments, abundant in animal diversity surrounded by fluids with specific physiological and chemical composition. Bathymodiolus azoricus mussels are endemic species dwelling at hydrothermal vent sites and at distinct depth ranges. Mussels from Menez Gwen (MG), Lucky Strike (LS), Rainbow (Rb) were collected at 800 m, 1730 m and 2310 m depths respectively, along the Mid-Atlantic Ridge. Five different tissues including gill, digestive gland, mantle, adductor muscle and foot from MG, LS and Rb mussels were selected for gene expression analyses by qPCR. 30 genes were tested to investigate the level of immune and apoptotic gene expression among B. azoricus populations. Statistical analyses confirmed tissue-specific gene expression differences among the five tissues. The digestive gland tissue showed a higher transcriptional activity characterized by an up-regulation of gene activities, contrary to what was assessed in the adductor muscle tissue. Five categories included recognition, signaling, transcription, effector and apoptotic genes were analyzed in this study. The majority of genes differed in levels of expression between MG/LS and LS/Rb in the digestive gland. Our findings suggest that gene expression profiles are inherent to the tissue analyzed, thus implying an immune tissue-specificity controlling defense responses across B. azoricus mussel body as a whole.