Organic matrix composition and ultrastructure of eggshell: a comparative study

1. The avian eggshell is a biomineralised composite ceramic consisting of c alcium carbonate embedded in an organic matrix. Matrix components are suppo sed to be involved in the control of mineralisation, crystallographic textu re and biomechanical properties of eggshell. 2. The structure and eggshell matrix composition of various domesticated bi rd species were compared to gain insight into the universality of the eggsh ell mineralisation process. 3. The SDS-PAGE profiles of soluble eggshell matrix were specific within gr oups of birds (a: laying hen, breeder hen, quail, pheasant and possibly tur key; b: guinea fowl; c: duck and goose) but some of the protein bands were common to all groups. 4. Analogies between species were confirmed by Western blotting using hen p rotein antibodies. Ovocleidin-17 (OC-17) and ovalbumin were revealed in all species (except quail for OC-17). Lysozyme was present only in hen eggshel l. Another egg white protein: ovotransferrin showed a positive signal in he ns, turkey and quail. Osteopontin was observed in laying and breeder hens a nd quail. 5. Different proteoglycans were localised to discrete regions within the eg gshell. Dermatan sulphate was observed within the matrix of the calcified s hell of all species except quail which contained chondroitin-6-sulfate. Ker atan sulphate was observed in mammillary bodies of breeder and laying hen, quail, pheasant and turkey while chondroitin sulphate was also present in g uinea fowl and duck. 6. The general structural organisation of the different avian eggshells was similar but specific differences were observed in the ultrastructure of th e mammillary layer. Species of the same taxonomic family could be grouped a ccording to their structural analogies: breeder hen, turkey and pheasant re sembled that of the domestic fowl. Guinea fowl was unique. Goose and duck w ere quite similar with large and confluent mammillary bodies. 7. Some matrix components are therefore common to eggshells of various spec ies but more information is needed to relate differences in matrix composit ion between taxonomic groups with differences in ultrastructure.