Importance Of Pearls

From ancient times, pearl has always been a highly sought after treasure for the gorgeous luster. Pearl, especially of the nacre structure, because of their unique microstructure and excellent mechanical properties, has been the focus of scientific research in recent years. The formative process of natural pearl involves the forming the pearl sac by the rapid proliferation of the epithelial cell of mantle followed by CaCO3 ordered deposition with a proper outside stimulation.
In the pearl industry, the standard operating procedure of grafting process is a mantle graft referred to as saibo selected from the region responsible for shell nacreous layer mineralization was implanted into the mantle of the host oyster for non-nucleated pearl production,

In pearl crystallizing layers, the most common mineral phase of CaCO3 includes calcite, aragonite and vaterite. The content of different CaCO3 mineral phases plays a decisive role in determining pearl quality. In high quality freshwater pearls, crystallizing layers are formed by aragonite crystals, and lamellaes are parallel to each other. In low quality freshwater pearls, vaterite and aragonite were found in prismatic layer in addition to aragonite nacreous layers. In seawater pearl, vaterite is absent, and the prismatic layer in low quality pearls is composed by calcite[1]. The organic matrix as the elementary element of pearls accounts for 5% (w/w) in the calcified layer. During the process of crystal accumulation, matrix proteins, the major components of organic matrix, embedded in intercrystalline for providing nucleation site, controlling crystal growth and accelerating polymorphic

To determine the genetic contribution of mantle allograft and recipient oyster in the course of pearl formation, many experimental studies in the molecular aspect have been presented to research the pearl sac. Arnaud-Haond et al confirmed the genome of donor was detected in the pearl sac by using microsatellite genetic markers[9]. Tetsuji Masaoka et al determined the type of nucleotide sequence of matrix protein N16 and N19 in pearl sac was same with those in donor mantle[10]. McGinty et al compared the quality traits of pearls formed by mantle xenografts between P. maxima and P. margaritifera and allograft in same species, results showed several quality traits such as nacre deposition color and complexion were influenced by mantle xenografting[11]. Subsequently, McGinty et al performed the transcriptome analysis of xenografted pearl sacs, and confirmed the putative biomineralization genes expressed in pearl sac was detected in donor oyster by species-diagnostic single nucleotide polymorphisms[12]. All the results indicate the donor mantle is survived in host oyster and involves in pearl sac formation and primarily participates in pearl