Ovotransferrin is a matrix protein of the hen eggshell membranes and basalcalcified layer

The eggshell is an highly ordered structure deposited in the distal oviduct and composed of calcium carbonate and an organic matrix which is believed to influence its fabric. We have identified ovotransferrin as an 80kDa matr ix protein observed at high concentration in the uterine fluid at the initi al stage of shell mineralization, by N-terminal sequencing and western blot ting using monoclonal and polyclonal antibodies. It is present in extracts from demineralized eggshell and was localized by immunofluorescence in the eggshell membranes and mammillae, which are the sites of calcite nucleation . Northern blotting and RT-PCR demonstrated that ovotransferrin message was expressed in the proximal oviduct (magnum and white isthmus), and at a low er magnitude in the distal oviduct (red isthmus and uterus). Ovotransferrin was revealed by immunofluorescence in the tubular gland cells of the uteru s. Calcium carbonate crystals grown in vitro in the presence of purified ov otransferrin showed large modifications of the calcite morphology. These ob servations and its presence in eggshell and membranes suggest a dual role f or ovotransferrin, as a protein influencing nucleation and growth of calcit e crystals and as a bacteriostatic filter to reinforce its inhibition of Sa lmonella growth in egg albumen.