Molecular cloning and characterisation of scavenger receptor class B in pearl oyster Pinctada fuctada martensii

Background: Molluscs can accumulate carotenoids in their body tissues by predominantly feeding on aquatic plant sources. Carotenoid transport and absorption are determined by the regulation of various proteins such as Scavenger receptor class B(SR-BI). We report the identification and characterisation of pearl oyster Pinctada fuctada martensii SR-BI (PmSR-BI). The correlation between total carotenoid content (TCC) and gene expression was also estimated.
Results: The full-length cDNA of PmSR-BI was 1828 bp, including an open-reading frame encoding of 1518 bpwith a pI value of 5.83. PmSR-BI protein contains a hydrophobic CD36 domain and four centrally clustered cysteine residues for the arrangement of disulphide bridges. The deduced amino acid sequence had an identity of 30% to 60% with the SR-B of other organisms. Reverse transcription polymerase chain reaction analysis showed that mRNA transcripts were expressed in multiple tissues of adult pearl oyster. A higher expression of PmSR-BI gene was observed in the hepatopancreas than in the adductor muscle, gill and mantle. The TCC and gene expression of PmSR-BI were significantly correlated (P < 0.05), with a correlation coefficient of 0.978.
Conclusions: The results suggested that PmSR-BI is involved in the absorption of carotenoids in the pearl oyster P. fuctada martensii.

Keywords
Carotenoids; cDNA; Gene expression; Hydrophobic pigments; Isoprenoid pigments; Marine bivalve molluscs; Precursor of abscisic acid; Precursor of phytohormones; RNA extraction; Saltwater oysters; Vitamin a