PfSMAD1/5 Can Interact with PfSMAD4 to Inhibit PfMSX to Regulate Shell Biomineralization in Pinctada fucata martensii

Molecular cloning and functional characterization of KCNQ1 in shell biomineralisation of pearl oyster Pinctada fucata martensii

KCNQ1, a voltage-gated potassium ion channel, plays an important role in various physiological processes, including osteoblast differentiation in higher animals. However, its function in lower invertebrates such as marine shellfish remains poorly understood. Pearl oysters, such as P. fucata martensii, are ideal for studying biomineralisation. In this study, a full-length cDNA of KCNQ1 from P. fucata martensii (PfKCNQ1) was obtained, and its function in shell formation was investigated. The full-length 3945 bp cDNA of PfKCNQ1 included an open reading frame (ORF) of 1944 bp encoding a polypeptide of 647 amino acids. Multiple sequence alignment revealed high homology with KCNQ1 from other species, with six transmembrane domains (S1 - S6) and a pore (P) region. Expression pattern analysis showed that PfKCNQ1 was expressed in all tested tissues, with highest expression in mantle and heart, and shell notching induced PfKCNQ1 expression. Silencing PfKCNQ1 expression inhibited PfKCNQ1 expression and downregulated four biomineralisation-related genes (Shematrin, Pif80, N16 and MSI60). Disordered crystals or "hollows" were visible in the shell ultrastructure by scanning electron microscopy following PfKCNQ1 knockdown. The results suggested that PfKCNQ1 may participate in or regulate biomineralisation and shell formation in pearl oyster.

The role of Smad1/5 in mantle immunity of the pearl oyster Pinctada fucata martensii

The Smad protein family is an important medium for transducing BMP-Smads signals, and which have been proved that their important role in regulating shell biomineralization in Pinctada fucata martensii in our previous study. The members of TGF-β superfamily were involved in innate immunity in vertebrates and invertebrates, and Smad regulatory networks construct a balanced immune system. However, little is known about the role of Smad1/5 in immunity in P. f. martensii. The present study shows that the tissue distribution and the expression profiles of Smad1/5 at developmental stages suggested its wide distribution and crucial role in development at embryonic stages other than larval stage; the increased expression of bone morphogenetic proteins 2 (BMP2), Smad4, Smad1/5 and MSX mRNAs at mantle tissue after LPS and Poly (I:C) challenged implied the potential immune role of Smad1/5 and BMP2-Smad signals to defense against bacterial and virus infections; the reduced expression of immune gene nuclear factor kappa-B (NF-κB), matrix metalloproteinase (MMP), interleukin 17 (IL-17), CuZn-superoxide dismutase (CuZn-SOD), tissue inhibitors of metalloproteinase (TIMP) and lipopolysaccharide-induced TNF-α factor (LITAF) mRNA following knockdown of Smad1/5 indicated that Smad1/5 can regulate their expression via BMP2-Smads pathway in the immunity process; the up-regulated expression of Smad1/5 and BMP2-Smad signals genes, and immune genes during wound healing indicated that Smad1/5 and BMP2-Smad signals genes may be involved in wound healing collaborated with immune genes via a different and complex Smads signaling pathway. These results indicated Smad1/5 could regulate innate immunity via BMP2-Smads signal pathway, and which provided new insights into the relationship between BMP2-Smads signal pathway and mantle immunity.