Abstract
Mounting evidence suggests that TGFβ/BMP signaling pathway is most likely involved in shell biomineralization in molluscs, but the function of pathway receptors is poorly studied. Here, we cloned and identified two homologous BMP receptor genes, PfBMPR1B and PfBAMBI, from the pearl oyster Pinctada fucata. Real-time quantitative PCR and in situ hybridization revealed that these genes were expressed in mantle edge and pallial, specifically located at the outer epithelia. Knockdown of PfBMPR1B by RNA interference (RNAi) significantly decreased the expression levels of matrix protein (MP) genes and induced the abnormal ultrastructure of prismatic and nacreous layers. Conversely, knockdown of PfBAMBI significantly increased the expression levels of a portion of MP genes and induced the overgrowth of nacreous layer crystals. In the RNAi and shell notching experiments, MP gene expressions were competitively regulated by PfBMPR1B and PfBAMBI. In addition, the receptor inhibitor LDN193189 reduced the expression levels of MP genes in mantle primary cells and larvae, and induced abnormal D-shaped shell formation during larval development. Collectively, these results clearly show that PfBMPR1B and PfBAMBI are involved in regulating shell biomineralization in P. fucata. Our study therefore provides the direct evidence that BMP receptors participate in mollusc biomineralization.
Highlights
Biomineralization is a widespread process in which inorganic ions orderly accumulate and deposit on the intracellular or extracellular matrix under the guidance of biomacromolecules in living organisms[1]
Functional analysis revealed that the Bmpr1b protein has a signal peptide (SP) from 1 amino acids (AA) to AA, a binding domain (BD) from AA to AA and a transmembrane domain (TD) located at the position ranging from AA to 160 AA
The obtained results here provide the first direct evidence that bone morphogenetic protein (BMP) receptors participate in mollusc biomineralization
Summary
Biomineralization is a widespread process in which inorganic ions orderly accumulate and deposit on the intracellular or extracellular matrix under the guidance of biomacromolecules in living organisms[1]. Analysis of the larvae of the brachiopod Lingula anatina revealed that SMAD1/5/9 was activated at the anterior margin of the mantle lobe during larval shell formation[16] All these findings propose a hypothesis that the TGFβ/BMP signaling pathway is highly likely to be associated with shell biomineralization. We identified two receptor genes, PfBAMBI and PfBMPR1B, of the TGF-β/BMP signaling pathway from P. fucata and clarified their roles in shell biomineralization regulation. The mantle primary cells and larval stage of P. fucata were exposed to the receptor inhibitor LDN193189 to further confirm the involvement of type I receptors, PfBMPR1B, in shell biomineralization These results will provide direct evidence regarding whether the BMP receptors participate in the regulation of shell biomineralization in pearl oysters and verify the hypothesis that TGFβ/BMP signaling pathway regulates mollusc biomineralization
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