A Preliminary Study on the Pattern, the Physiological Bases and the Molecular Mechanism of the Adductor Muscle Scar Pigmentation in Pacific Oyster Crassostrea gigas.

Wenchao Yu,Wen Guo,Qiuyun Jiang,Cheng He,Lei Wei,Zhongqiang Cai,Na Wei,Zhuang Li,Xiaotong Wang,Fei Xu,Jun Chen

doi:10.3389/fphys.2017.00699

Abstract

The melanin pigmentation of the adductor muscle scar and the outer surface of the shell are among attractive features and their pigmentation patterns and mechanism still remains unknown in the Pacific oyster Crassostrea gigas. To study these pigmentation patterns, the colors of the adductor muscle scar vs. the outer surface of the shell on the same side were compared. No relevance was found between the colors of the adductor muscle scars and the corresponding outer surface of the shells, suggesting that their pigmentation processes were independent. Interestingly, a relationship between the color of the adductor muscle scars and the dried soft-body weight of Pacific oysters was found, which could be explained by the high hydroxyl free radical scavenging capacity of the muscle attached to the black adductor muscle scar. After the transcriptomes of pigmented and unpigmented adductor muscles and mantles were studied by RNAseq and compared, it was found that the retinol metabolism pathway were likely to be involved in melanin deposition on the adductor muscle scar and the outer surface of the shell, and that the different members of the tyrosinase or Cytochrome P450 gene families could play a role in the independent pigmentation of different organs.

Highlights

As we all know, shell color is one of most attractive features of mollusks
The quantity of oysters whose outer surface of the left shell and left adductor muscle scar differed in color was calculated in each farm; that of oysters whose outer surface of the right shell and right adductor muscle scar differed in color was done in each farm
Number of oysters whose outer surface of the right shell and right adductor muscle scar differed in color in order to observe the obvious dissimilarity, only the oysters with completely pigmented and unpigmented muscle scar or outer shell were applied to the correlation analysis between pigmentation and soft-body dry weight

Summary

Introduction

Shell color is one of most attractive features of mollusks. Current research into the pigmentation of mollusks is mainly focused on carotenoids in the shell and soft body (Li et al, 2010; Zheng et al, 2010, 2012; Maoka, 2011; Maoka et al, 2014; Liu et al, 2015; Williams, 2017), which have roles in quenching singlet oxygen species, eliminating free radicals, acting as antioxidants, and supporting the immune system (Rao and Rao, 2007; Maiani et al, 2009). Melanin has a similar biological function as carotenoids (Kollias et al, 1991; Sharma et al, 2002), and it has been confirmed that the black pigment in the soft body, outer surface of the shell, and adductor muscle scar of oysters is melanin (Hao et al, 2015; Yu et al, 2015; Williams, 2017). Researchers viewed Pacific oyster shell pigmentation as a continuously distributed, quantitative trait under polygenic control (Brake et al, 2004; Batista et al, 2008), but in recent cases, shell coloration was determined to be controlled by a small quantity of major genes or be under relatively high genetic control with the moderateto-high narrow-sense heritability value (Sanford et al, 2009; Ge et al, 2015; Wan et al, 2017). The diversity of adductor muscle scar color was observed in Crassostrea angulata or Crassostrea gigas (Batista et al, 2008; Higuera-Ruiz and Elorza, 2011)

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