12.4.4 Pearl Quality
Although several genes encoding matrix proteins from pearl oyster nacreous layers
and the gene expression profile in different region of mantle (Takeuchi and Endo
2006) and in the pearl sac (Wang et al. 2009) have been characterized by real-time
PCR, research on the function of matrix proteins has mainly focused on their effects
on calcium carbonate crystallization in vitro. Research on the functions of matrix
proteins rarely concern pearl quality. Recently, Inoue et al. (2010) used real-time
PCR analysis to investigate the relationship between pearl quality and gene expression patterns of six shell matrix proteins involved in nacreous and prismatic layer
formation in the pearl sac. They discovered that the relative expression level of
MSI31, which encodes a framework protein in the prismatic layer, is higher in the
pearl sac producing lower-quality pearls than in that producing high-quality ones
(Inoue et al. 2010). Their findings provide a new possibility to improve the quality
of pearls by inhibiting the expression level of some specific genes involved in
prismatic layers in the early stage of pearl formation.
12.5 The Molecular Mechanism Involved in Nacreous
Biomineralization
Investigations of the mechanism of nacre biomineralization mainly focus on two
aspects: (1) the nucleation and growth of aragonite crystal; (2) the orientation of
crystal growth.
12.5.1 The Nucleation and Growth of Aragonite Crystal
Several models related to nacre biomineralization have been proposed. According
to the early compartments model, compartments are first formed on lamellae
parallel to the surface of the epithelium in which crystal nucleation is initiated in
contact with a crystal in an adjacent layer (Bevelander and Nakahara 1969). The
uniform thickness, orientation, and other features exhibited in the mature nacre are
determined by the compartments. This model is partly supported and modified by
the Voronoi model, which suggests that the mature nacre layer first existed as a film
(opened compartment), on which the crystal nucleation occurs in time and space
probably stimulated by a signal coming from an underlying layer. Then there is
progressive lateral crystallization, and consequently formation of polygonal tablets
of bio-aragonite. The growth of the tablets is controlled by an “aggregation-like”
process of small “crystallites” (Rousseau et al. 2005a).
The “generally accepted” template theory indicates that the organic matrix
constructs a framework which acts as a template for calcium carbonate crystal
344
L.-p. Xie et al.
Although several genes encoding matrix proteins from pearl oyster nacreous layers
and the gene expression profile in different region of mantle (Takeuchi and Endo
2006) and in the pearl sac (Wang et al. 2009) have been characterized by real-time
PCR, research on the function of matrix proteins has mainly focused on their effects
on calcium carbonate crystallization in vitro. Research on the functions of matrix
proteins rarely concern pearl quality. Recently, Inoue et al. (2010) used real-time
PCR analysis to investigate the relationship between pearl quality and gene expression patterns of six shell matrix proteins involved in nacreous and prismatic layer
formation in the pearl sac. They discovered that the relative expression level of
MSI31, which encodes a framework protein in the prismatic layer, is higher in the
pearl sac producing lower-quality pearls than in that producing high-quality ones
(Inoue et al. 2010). Their findings provide a new possibility to improve the quality
of pearls by inhibiting the expression level of some specific genes involved in
prismatic layers in the early stage of pearl formation.
12.5 The Molecular Mechanism Involved in Nacreous
Biomineralization
Investigations of the mechanism of nacre biomineralization mainly focus on two
aspects: (1) the nucleation and growth of aragonite crystal; (2) the orientation of
crystal growth.
12.5.1 The Nucleation and Growth of Aragonite Crystal
Several models related to nacre biomineralization have been proposed. According
to the early compartments model, compartments are first formed on lamellae
parallel to the surface of the epithelium in which crystal nucleation is initiated in
contact with a crystal in an adjacent layer (Bevelander and Nakahara 1969). The
uniform thickness, orientation, and other features exhibited in the mature nacre are
determined by the compartments. This model is partly supported and modified by
the Voronoi model, which suggests that the mature nacre layer first existed as a film
(opened compartment), on which the crystal nucleation occurs in time and space
probably stimulated by a signal coming from an underlying layer. Then there is
progressive lateral crystallization, and consequently formation of polygonal tablets
of bio-aragonite. The growth of the tablets is controlled by an “aggregation-like”
process of small “crystallites” (Rousseau et al. 2005a).
The “generally accepted” template theory indicates that the organic matrix
constructs a framework which acts as a template for calcium carbonate crystal
344
L.-p. Xie et al.