[Frontiers in Bioscience S4, 1099-1125 , January 1, 2012]

The formation and mineralization of mollusk shell

Frederic Marin1, Nathalie Le Roy1, Benjamin Marie1

1UMR CNRS 5561, Biogeosciences, Universite de Bourgogne, 6 Boulevard Gabriel, 21000 Dijon, France

TABLE OF CONTENTS

1. Abstract
2. Mollusk shell
2.1. Introduction
2.2. Diversity of mollusk classes
3. Structural, microstructural and ultrastructural considerations on the shell
3.1. Structure of the shell and mineralogy
3.2. Different shell microstructures
3.3. Nacre: organization and ultrastructure
3.3.1. Why nacre is interesting to study
3.3.2. Brief definition of nacre
3.3.3. Complex organo-mineral interactions
3.3.4. Mechanism of nacre formation
4. Early stages of shell calcification: developmental aspects
4.1. Formation of the shell in relation with larval development
4.2. Genes and their products involved in the larval shell construction
5. Shell formation: physiological and cellular considerations
5.1. Calcification of the shell in normal conditions
5.1.1. Mantle and cells of the outer epithelium
5.1.2. Periostracum
5.1.3. Interface between the mantle and the shell
5.1.4. Transport of the precursor ions of mineralization
5.1.5. Synthetic cellular view of the shell formation process
5.2. Shell remodeling and shell repair process
5.3. A critical view of the standard model
6. Organic constituents of the shell
6.1. Biochemistry of the mollusk shell
6.2. Non protein organic shell components
6.2.1. Polysaccharides
6.2.2. Lipids, pigments, and other small organic molecules
6.3. Shell proteins
6.3.1. Biochemistry of shell proteins
6.3.2. Shell proteins: the "protein per protein" approach
6.3.3. Shell proteins: large screening of the "shellome"
7. Perspectives and future directions
8. Acknowledgements
9. References

1. ABSTRACT

In the last years, the field of mollusk biomineralization has known a tremendous mutation. The most recent advances deal with the nanostructure of shell biominerals, and with the identification of several shell matrix proteins: on one hand, the complex hierarchical organization of shell biominerals has been deciphered in few models, like nacre. On the other hand, although proteins represent a minor shell component, they are the major macromolecules that control biocrystal synthesis. Until recently, the paradigm was to consider that this control occurs by two antagonist mechanisms: crystal nucleation and growth inhibition. Emerging models try to translate a more complex reality, illustrated by the huge variety of shell proteins, characterized so far. The primary structure of many of them is composed of different functional domains, some of which exhibit enzymatic activity, while others may be involved in cell signalling. Many of them have unknown functions. Today, the shell matrix appears as a whole system, which regulates protein-mineral, protein-protein, and epithelium-mineral interactions. These aspects should be taken in account for the future models of shell formation.