A Cartilage Matrix Protein Regulates Collagen Synthesis in Mantle of Magallana gigas (Crassostrea gigas) under Ocean Acidification

Abstract

The shell biosynthesis of oysters plays a critical role in protection against environmental stress, in which cartilage matrix proteins (CMPs) determine the mineralogical and crystallographic properties of the shell. In the present study, a cartilage matrix protein (designated as MgCMP1) was identified from the Pacific oyster Magallana gigas (Crassostrea gigas) with the objective of understanding its possible role in shell formation. The open reading frame (ORF) of MgCMP1 was 1815 bp, encoding a polypeptide of 605 amino acids with two von Willebrand factor (VWA) domains. The mRNA transcript of MgCMP1 was expressed constitutively in all examined tissues with a higher level in the mantle, especially highest in the middle fold (MF) of the three folds of the mantle. In addition, the interaction between recombinant protein MgCMP1 (rMgCMP1) and recombinant protein bone morphogenesis protein 7 (rMgBMP7) was identified in vitro. After injection of dsRNA to inhibit the expression of MgCMP1, the mRNA expression level of Mgcollagen I and Mgcollagen X in the MF of the mantle significantly decreased. After pre-puncturing and acidification treatment (pH 7.8), the thickness and length of the new formation shells were lower than those in control group (pH 8.1), and the positive hybridization signals of the MgCMP1 mRNA transcript in the three mantle folds were obviously weakened, especially in the MF, whereas the mRNA expression level of MgCMP1, Mgcollagen I and Mgcollagen X in the MF of mantle decreased significantly. These results suggested that MgCMP1 was involved in regulating the expression of Mgcollagen I and Mgcollagen X in the MF of the mantle in response to ocean acidification (OA).