Abstract
BackgroundDespite its economic importance, we have a limited understanding of the molecular mechanisms underlying shell formation in pearl oysters, wherein the calcium carbonate crystals, nacre and prism, are formed in a highly controlled manner. We constructed comprehensive expressed gene profiles in the shell-forming tissues of the pearl oyster Pinctada fucata and identified novel shell formation-related genes candidates.Principal FindingsWe employed the GS FLX 454 system and constructed transcriptome data sets from pallial mantle and pearl sac, which form the nacreous layer, and from the mantle edge, which forms the prismatic layer in P. fucata. We sequenced 260477 reads and obtained 29682 unique sequences. We also screened novel nacreous and prismatic gene candidates by a combined analysis of sequence and expression data sets, and identified various genes encoding lectin, protease, protease inhibitors, lysine-rich matrix protein, and secreting calcium-binding proteins. We also examined the expression of known nacreous and prismatic genes in our EST library and identified novel isoforms with tissue-specific expressions.ConclusionsWe constructed EST data sets from the nacre- and prism-producing tissues in P. fucata and found 29682 unique sequences containing novel gene candidates for nacreous and prismatic layer formation. This is the first report of deep sequencing of ESTs in the shell-forming tissues of P. fucata and our data provide a powerful tool for a comprehensive understanding of the molecular mechanisms of molluscan biomineralization.
Highlights
Because of its high industrial value, nacreous layer formation in the pearl oyster is a well-studied phenomenon
We constructed EST data sets from the nacre- and prism-producing tissues in P. fucata and found 29682 unique sequences containing novel gene candidates for nacreous and prismatic layer formation. This is the first report of deep sequencing of ESTs in the shell-forming tissues of P. fucata and our data provide a powerful tool for a comprehensive understanding of the molecular mechanisms of molluscan biomineralization
The shell of pearl oysters consists of 2 distinct structures: inner nacreous layers composed of aragonite and outer prismatic layers composed of calcite
Summary
Because of its high industrial value, nacreous layer formation in the pearl oyster is a well-studied phenomenon. Pearl oysters initiate shell formation with amorphous calcium carbonate, which is transformed into either calcite or aragonite [2,3,4] These transformation processes are thought to be regulated by proteins secreted from epithelial cells in outer mantle tissues [1,5]. These proteins form a biomineral framework and regulate the nucleation and growth of calcium carbonate. Pearl sac tissues are formed by proliferation of epithelial cells originating from the outer mantle graft where various proteins are secreted to form the nacreous layers [7,8] (see Fig. 1A). We constructed comprehensive expressed gene profiles in the shell-forming tissues of the pearl oyster Pinctada fucata and identified novel shell formation-related genes candidates
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