Search

• •Knockdown Mitf obviously decreased expression of tyrosinase family genes, tyrosinase activity and melanosome count in mantles. • • Mitf was involved in transcriptional regulation of Typ-2 and Typ-3 genes through binding to their specific promoter regions. • • Mitf are assositated with shell pigmentation by activating tyrosinase-mediated melanin synthesis in Pacific oyster. Pigmentation is frequently observed in the molluscan shells, whereas the molecular regulation about these shell pigments formation is not clear. The microphthalmia-associated transcription factor (Mitf) is an important transactivator in melanin synthesis in vertebrates. Here, the Mitf containing a highly conserved basic helix-loop-helixleucine zipper (bHLH-LZ) domain was identified in an economically important marine bivalve Pacific oyster Crassostrea gigas. The Mitf was found to widespread tissue distribution and the expression was higher in the marginal mantle than in the central mantle. Particularly, the expression level of Mitf was high in black shell color oysters compared with white shell oysters. After injecting siRNA, the expression of Mitf decreased significantly, and the efficiency of RNA interference reached 53%. Besides, knockdown Mitf obviously decreased expression of tyrosinase family genes and tyrosinase activity of mantles, indicating a potential regulatory relationship between Mitf and Tyr or Typs. Simultaneously, there was a sharply reduce in the number of the melanosomes in the outer fold of mantle by silencing of Mitf. Luciferase assays in cell culture further verified that Mitf was involved in transcriptional regulation of Typ-2 and Typ-3 genes through binding to their specific promoter regions. These data argue that Mitf is involved in shell pigmentation through activating tyrosinase-mediated melanin synthesis in C. gigas. [ABSTRACT FROM AUTHOR]

The shell color of Pacific oyster (Crassostrea gigas) is a desirable trait; but the nutritional studies on C. gigas with different shell colors have not been conducted. Through successive selective breeding, five shell color strains of black (B), purple (P), orange (O), golden (G) and white (W) C. gigas have been developed. The aim of this study was to evaluate the chemical composition and nutritional value of five shell color strains and one commercial population with a common color. The biochemical composition including moisture, total protein, glycogen, ash, total fat, fatty acids (FA), amino acids and minerals was detected. The results indicated that the protein (50.76%-56.57%) was the major component. The content of glycogen showed a significant difference between orange shell and golden shell strains, as well as between commercial population and golden shell strain. In addition, all shell color strains contained a large amount of essential amino acids (12.20-14.15 g (100 g)−1), of them leucine (2.81-3.29 g (100 g)−1) and lysine (2.79-3.28 g (100 g)−1) were predominant. The oysters were rich in polyunsaturated fatty acids (42.26%-45.24% of total fatty acid) with high levels of DHA (18.53%-21.16% of total fatty acid) and EPA (17.23%-18.68% of total fatty acid). Significant differences of mineral contents (Mg, Zn, Fe and Cu) were identified among the six populations. These results indicated that C. gigas with different shell colors presented rich nutritional value with high protein, glycogen, essential amino acids and polyunsaturated fatty acids. The biochemical composition obtained in this study is useful for selective breeding of C. gigas with different shell colors. [ABSTRACT FROM AUTHOR]

• CgTyp-1 and CgTyp-3 were expressed at higher levels in the black shell than that in the white shell color oysters. • Two tyrosinase-like genes were located in the outer epithelium of the outer fold either in the black or white shell color oysters. • Knockdown of each Typ resulted in obvious decreases of the tyrosinase activity and melanosome count in mantles. • CgTyp-1 and CgTyp-3 were involved in the biosynthesisof melanin. Color polymorphism in Mollusca is of great interest for consumer preference. Although the heritability of shell color variation has been conducted by experimental crossing, little is known about molecular basis involved in these patterns. Tyrosinase-like proteins are important enzymes which are members of the type-3 copper protein superfamily. In this research, two tyrosinase-like protein genes including CgTyp-1 and CgTyp-3 were identified in the Pacific oyster Crassostrea gigas. Tissue expression analysis showed that CgTyp-1 and CgTyp-3 were dominantly expressed in the mantle. Particularly, they were expressed significantly higher in the edge mantle than that in the central mantle whether on the left or right mantles. Additionally, expressions of CgTyp-1 and CgTyp-3 were mainly found in the black shell color oysters, with relative lower levels in the white shell color oysters. In situ hybridization showed that positive signals for CgTyp-1 and CgTyp-3 were both detected within the outer epithelium of the outer fold either in the black or white shell color oysters. After interference, the expression levels of CgTyp-1 and CgTyp-3 mRNA were significantly attenuated, and the efficiency of RNAi reached 84.72% and 71.58%, respectively. Besides, knockdown CgTyp-1 or CgTyp-3 , obviously decreased the tyrosinase activity of mantles. Furthermore, the number of the melanosomes within epithelium of the outer fold was sharply reduced by silencing of each Typ. These findings argue that CgTyp-1 and CgTyp-3 may be involved in the melanin synthesis, which lends insight into regulation mechanism of shell pigmentation in C. gigas. [ABSTRACT FROM AUTHOR]