Comparative Analysis Of Immunity Between Black Shell And White Shell Crassostrea Gigas

Melanin is widely found in many organisms and is one of the main pigments that can be synthesized by mollusks in vivo.Melanin pigmentation in animals is not only a unique coloring mechanism,but also shows a variety of biological activities,including multiple immune functions,such as removing free radicals,killing bacteria,and inhibiting oxidative damage.Analysis of immune functions has been a focus of melanin pigmentation research.The Pacific oyster is a valuable aquacultural species around the world and is usually used as a model for the research on mollusks.Differences in melanin pigmentation are usually found in the shells and mantles of Pacific oyster individuals.Preliminary studies established a method to extract melanin from Pacific oysters,and showed that melanin pigmentation in Pacific oyster shells is significantly correlated with the melanin content in mantle tissues.Nevertheless,the functions of melanin in Pacific oyster are unclear,especially those related to immunity.In this study,differences in immune function between two types of Pacific oyster(differing in terms of their melanin content)were evaluated at the physiological,molecular and toxicological level.The main results are as follows:1.By comparing the immune indexes,the differences in the immune abilities of Crassostrea gigas with black shell and white shell were analyzed: Initially,grayscale comparisons were used to screen out the shell color and to establish two experimental groups: black-shelled Pacific oysters(B)and white-shelled Pacific oyster(W).Then,changes in melanin content and various immunity-related indicators were analyzed to compare the differences in the mantle tissues of BSO and WSO.Moreover,RNA-Seq was used to compare the differentially expressed immune-related genes between these two types of Pacific oyster.2.The effect of environmental endocrine disruptor(bisphenol A)on the immunity of Crassostrea gigas with black shell and white shell were analyzed: Firstly,high performance liquid chromatography-mass spectrometry(HPLC-MS/ MS)was used to determine the content of bisphenol A(BPA)in the mantle of white shell and black shell oyster in natural seawater.It was found that the content of BPA in the mantle of black shell oyster was lower than that of white shell oyster(P < 0.05).Since tyrosinase,a key enzyme in the synthesis of melanin,is a phenol oxidase,which can catalyze the oxidation of phenols or aromatic amines and other substrates,it is speculated that tyrosinase also plays an important role in the degradation of phenolic toxicants such as BPA.To further investigate the the differences in the ability of BPA degradation and damage resistance between oysters with different melanin contents,subchronic exposure experiments of BPA with concentrations of 1 mg/ L,1.5 mg/ L and 2 mg/ L were performed in this study.Through the analysis of the BPA content in the mantle tissues of Crassostrea gigas after exposure,it was found that the BPA content in mantle of white and black shell oyster both increased with the rise of exposure concentration.In addition,after chronic exposure to BPA at the three concentrations,the BPA content in mantle of black shell oyster was lower than that of white shell oyster,but the difference was not significant(P > 0.05).The fluorescence value of reactive oxygen species(ROS)in mantle of black shell oyster was significantly lower than that of white shell oyster after chronic exposure to BPA at three concentrations(P < 0.01).The histological observation of the mantle revealed that BPA exposure caused obvious pathological changes in the mantle tissue of the white shell oyster,while there was no obvious pathological change in the mantle of the black shell oyster.It can be seen that the black shell oyster may have stronger resistance to BPA exposure.Based on the above experimental studies,the effect of melanin content on the immunity of Crassostrea gigas was preliminarily discussed,which provided abundant basic data for the in-depth study of the function of melanin in Marine organisms and the elucidation of the breeding advantages of Crassostrea gigas with high melanin content.