Ressource pédagogique : Prof. Marc McKee - The structure of avian (chicken) eggshell

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The functional properties of biomineralized structures found in Nature result from interactions between their hybrid components – both organic (mostly proteins) and inorganic (mineral) phases – to generate hierarchical organization across different length scales.  In its dual function, the calcitic avian eggshell provides a protective barrier for the enclosed developing chick embryo while also serving to provide calcium for the growing chick skeleton by the process of shell dissolution.  Here, a detailed structural analysis (including a description of nanostructure) is given for the eggshell produced by the domesticated chicken, along with changes that occur following eggshell dissolution – a shell-thinning and weakening process leading to hatching of the chick (pipping) which occurs after egg fertilization and incubation.  Eggshell contains abundant proteins, and the localization of some of these (particularly osteopontin) will be described at the ultrastructural level, and correlated with generating nanostructure and shell hardness.  X-ray and electron imaging and diffraction data, together with atomic force microscopy observations, describe an aligned nanostructure of mineral within the shell.  A similar nanostructure could be reproduced in synthetic calcite crystals by the simple addition of osteopontin, which becomes occluded within the calcite to generate this mineralization pattern.  Taken together, these findings are consistent with this protein's mineral-binding and regulatory role in biomineralization in a large number of biological systems, and point to a highly conserved, mineral nanostructure-regulating activity of osteopontin conserved over at least 300 million years of evolution.  

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• Biochimie (572)

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