[Frontiers in Bioscience 17, 1266-1280, January 1, 2012]

The eggshell: structure, composition and mineralization

Maxwell T. Hincke1, Yves Nys2, Joel Gautron2, Karlheinz Mann3, Alejandro B. Rodriguez-Navarro4, Marc D. McKee5

1Department of Cellular and Molecular Medicine, University of Ottawa, 451 Smyth Road, Ottawa, K1H 8M5, Canada, 2INRA, Institut National de la Recherche Agronomique, UR83 Recherches Avicoles, F-37380, Nouzilly, France, 3Max-Planck-Institut für Biochemie, Abteilung Proteomics und Signaltransduktion, Am Klopferspitz 18, D-82152 Martinsried, Germany, 4Minerology and Petrology, University of Granada, Granada, 18002, Spain, 5Faculty of Dentistry, and Department of Anatomy and Cell Biology, McGill University, Montreal, Quebec, H3A 2B2, Canada


1. Abstract
2. Introduction
3. Overview of eggshell: formation and structure
3.1. Eggshell calcification
3.2. Eggshell microstructure and crystallographic texture
4. Regulation of calcification by matrix constituents
4.1. Purified eggshell matrix constituents
4.2. Amorphous calcium carbonate
5. Eggshell matrix proteins
5.1. Eggshell matrix proteome
5.2. Transcriptomics
5.3. Genomics
5.4. Ovocleidin-17 (OC-17)
5.5. Ovocleidin-116 (OC-116)
5.6. Ovocalyxin-32 (OCX-32)
5.7. Ovocalyxin-36 (OCX-36)
5.8. Osteopontin (OPN)
6. Summary and Perspective
7. Acknowledgements
8. References


The calcareous egg is produced by all birds and most reptiles. Current understanding of eggshell formation and mineralization is mainly based on intensive studies of one species - the domesticated chicken Gallus gallus. The majority of constituents of the chicken eggshell have been identified. In this article we review eggshell microstructure and ultrastructure, and the results of recent genomic, transcriptomic and proteomic analyses of the chicken eggshell matrix to draw attention to areas of current uncertainty such as the potential role of amorphous calcium carbonate and the specific nature of the molecules that initiate (nucleate) mammillary cone formation and terminate palisade layer calcification. Comparative avian genomics and proteomics have only recently become possible with the publication of the Taeniopygia guttata (zebra finch) genome. Further rapid progress is highly anticipated with the soon-to-be-released genomes of turkey (Meleagris gallopavo) and duck (Anas platyrhynchos). These resources will allow rapid advances in comparative studies of the organic constituents of avian eggshell and their functional implications.