The role of avian eggshell matrix proteins in shell formation is poorly understood. This calcitic biomaterial forms in a uterine fluid where the protein composition varies during the initial, calcification, and terminal phases of eggshell deposition. A specific antibody was raised to a 116-kDa protein, which is most abundant in uterine fluid during active eggshell calcification. This antiserum was used to expression screen a bacteriophage cDNA library prepared using mRNA extracted from pooled uterine tissue harvested at the midpoint of eggshell calcification. Plasmids containing inserts of differing 5-lengths were isolated with a maximum cDNA sequence of 2.

The protein components of biomineralized structures (matrix proteins) are believed to modulate crystal nucleation and growth, and thereby influence the shape and strength of the final structure. The chicken eggshell contains a complex array of distinct matrix proteins. The most abundant of these was purified to homogeneity by a combination of anionic exchange and hydroxyapatite chromatographies. Antibodies to this protein were raised in rabbit, and utilized for Western blotting and immunohistochemistry. These studies indicated that the 17 kDa antigen (ovocleidin 17, OC-17) is found in the shell gland mucosa, and that only the tubular gland cells were positive. Immunohistochemistry with decalcified shell indicated that OC-17 is uniformly distributed throughout the shell matrix, but concentrated in the mammillary bodies. Our results indicate that this protein is secreted during shell formation and becomes incorporated into this structure. It may therefore play a role in the crystallization process and influence the properties of the resulting eggshell.

1. The protein components of the domestic fowl's eggshell are believed to influence appreciably the mechanical properties of the shell and/or its biomineralisation. The purpose of this study was to compare the protein species composing the eggshell matrix in different parts of the shell structure, by SDS-PAGE and chromatography, utilising eggshell cleaned by different methodologies. 2. Protein species were identified whose absence was associated with the removal of the mammillary knobs. In particular, a prominent 81 kDa protein, as well as 38 and 54 kDa calcium-binding proteins, were concentrated within the mammillary layer, as was a 129 kDa insoluble protein. By contrast, soluble proteins of 54, 33, 22, and 14 kDa were enriched in the palisade layer. 3. Our results demonstrate that the mineralised layers of the fowl's eggshell possess a complex array of distinct proteins. The different proteins which have been detected in the mammillary and palisade layers may be related to the distinct crystallisation patterns of calcium carbonate in these zones of the eggshell.

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