Creb (Cyclic AMP response element binding protein) is a nuclear regulatory factor that regulates transcription through autophosphorylation. In melanocytes, cAMP’s corresponding elements bind to the Creb protein to autophosphorylation and activate MITF (Microphthalmia-associated transcription factor). MITF stimulates Tyrosine(tyr) to induce melanocytes to differentiate into eumelanin and pheomelanin. In this study, a HcCreb gene in Hyriopsis cumingii was cloned and its effects on melanin synthesis and nacre color were studied. HcCreb was expressed in both purple and white mussels, and there was a significant difference in expression between adductor muscle (p<0.01) and mantle tissue (p<0.05). Other tissues did not show significant differences (except for gill tissue), and in general, the level of mRNA expression was higher in purple mussels than in white mussels. In both white and purple mussels expression levels in gill tissue was the highest, followed by the mantle. Strong and specific mRNA signals were detected in the dorsal epithelial cells of the mantle pallial layer, indicating that HcCreb may be involved in nacre formation. After arbutin treatment, the expression of HcCreb decreased significantly. By further testing the changes in mantle melanin content it was found that the melanin content after arbutin treatment decreased significantly compared to the control group (p<0.05). It is speculated that the HcCreb gene plays a role in the process of melanin synthesis and nacre color formation in H. cumingii.
Carotenoids play key roles in organism coloration and have been found to have an effect on shell color. Steroidogenic acute regulatory protein-like (StAR-like) is a key gene involved in the accumulation of carotenoids. In this study, the full-length cDNA sequence of HcStAR-like, containing 994 nucleotides with an open reading frame encoding 307 amino acid residues, was isolated from the freshwater pearl mussel, Hyriopsis cumingii. HcStAR-like expression levels were significantly higher in all tissues examined in golden (G-) mussels compared with white (W-) and purple (P-) mussels (p < .05). Moreover, although HcStAR-like expression levels were higher in P-mussels than W-mussels, this difference was only significant in the hepatopancreas (p < .05). Our in situ hybridization assay indicated that StAR-like was localized to the outer fold of the mantle and the joint of the outer and middle folds of the mantle.The dsRNA interference of HcStAR-like expression in Gmussels was effective with an interference rate of 79.89% (p < .05). The total carotenoid content (TCC) in the mantle of the RNAi group decreased by 48.63% (p < .05). Our Jinpan Zhang and Baiying Guo contributed equally to this study.
Background
Protein kinase C (PKC) is a multifunctional serine and PKC can phosphorylate serine residues in the cytoplasmic domain of tyrosinase, thereby regulating the activity of tyrosinase. Activated PKC is bound to the melanosome membrane, and unactivated PKC is free in the cytoplasm of melanocytes. In this study, we study the role of PKC gene in the melanin synthesis pathway and its effect on the color of the nacre of H. cumingii.
Results
In this study, a HcPKC gene in H. cumingii was cloned and its effects on melanin synthesis and nacre color were studied. HcPKC was expressed in both purple and white mussels, and the level of mRNA expression was higher in the purple mussels than in white mussels. Strong and specific mRNA signals were detected in the dorsal epithelial cells of the mantle pallial layer, indicating that HcPKC may be involved in nacre formation. After SNP association with inner shell color related traits, according to the principle that 0.25 < PIC < 0.5 is medium polymorphism and PIC < 0.25 is low polymorphism, the A + 332G site on the HcPKC gene was a site of moderate polymorphism, and the other four sites were low polymorphism sex sites. There was strong linkage disequilibrium among the five loci. A haplotype was constructed and it was found that the frequency of T1 (AGGAA)in the white population was significantly higher than that in the purple population (P < 0.05).
Conclusion
The study found that HcPKC of H. cumingii can be used as a candidate gene related to inner shell color, and some of the SNP sites can be used for molecular-assisted breeding in the spinnaker mussel, providing a reference for cultivating high-quality freshwater pearls.
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