Patterns of Expression in the Matrix Proteins Responsible for Nucleation and Growth of Aragonite Crystals in Flat Pearls of Pinctada fucata

Liang Xiang,Guilan Zheng,Liping Xie,Hongzhong Wang,Jian Liang,Jingtan Su,Guiyou Zhang,Rongqing Zhang,Partha Mukhopadhyay

doi:10.1371/journal.pone.0066564

Abstract

The initial growth of the nacreous layer is crucial for comprehending the formation of nacreous aragonite. A flat pearl method in the presence of the inner-shell film was conducted to evaluate the role of matrix proteins in the initial stages of nacre biomineralization in vivo. We examined the crystals deposited on a substrate and the expression patterns of the matrix proteins in the mantle facing the substrate. In this study, the aragonite crystals nucleated on the surface at 5 days in the inner-shell film system. In the film-free system, the calcite crystals nucleated at 5 days, a new organic film covered the calcite, and the aragonite nucleated at 10 days. This meant that the nacre lamellae appeared in the inner-shell film system 5 days earlier than that in the film-free system, timing that was consistent with the maximum level of matrix proteins during the first 20 days. In addition, matrix proteins (Nacrein, MSI60, N19, N16 and Pif80) had similar expression patterns in controlling the sequential morphologies of the nacre growth in the inner-film system, while these proteins in the film-free system also had similar patterns of expression. These results suggest that matrix proteins regulate aragonite nucleation and growth with the inner-shell film in vivo.

Highlights

Nacre is the lustrous internal ‘mother of pearl’ layer of many molluscan shells, and pearls themselves are structurally similar to the nacre of pearl oyster shells [1]
The growth of nacre in the flat pearl of Haliotis rufescens is well studied by many researchers [13,25,26,33,34]
The towered nacre grown in gastropod mollusks does not contain the hexagonal flat tablets with the stairlike growth pattern that is uniquely characteristic of the growing surface of the nacre produced by bivalves [29]

Summary

Introduction

Nacre is the lustrous internal ‘mother of pearl’ layer of many molluscan shells, and pearls themselves are structurally similar to the nacre of pearl oyster shells [1]. The structure of nacre is a brick and mortar arrangement: the bricks are flat polygonal crystals of aragonite, and the mortar is made out of polysaccharide chitin, lipids and proteins laid down orthogonally to each other and aligned with the aragonite crystal axes. This structure result in higher mechanical strength and osteoinductive activity compared with inorganic CaCO3 crystals [2,3]. Understanding the process by which living organisms control the growth of structured inorganic materials could lead to significant advances in materials science, and open the door to novel synthesis techniques for nanoscale composites [5,6,7]

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Conclusion