Proteomic study of inner and outer hen egg vitelline membranes: insights into the biological functions of vitelline membrane layers

International audienceThe hen egg vitelline membrane (VM) is a proteinaceous membrane separating the egg white from the yolk. The VM is involved in fertilization, in early stages of embryogenesis but also in protection of the embryo. It consists of the inner layer (IVM) and the outer layer (OVM), that are in contact with the yolk and the egg white, respectively. These two layers are synthesized by distinct tissues namely the ovary/liver for IVM and the oviduct for OVM. About 140 different proteins were identified in the VM to date; however, the distribution of most of these proteins between IVM and OVM remains to be elucidated. The VM contains several ZP proteins that are likely to be involved in sperm-oocyte interactions during fertilization. VM is also crucial for embryonic development as it provides a substratum for embryonic and yolk sac expansion in early incubation. Moreover, VM is a physical barrier protecting the embryo from the egg white alkalinity and from potential microbial contaminations, and the high amount of antimicrobials in VM (lysozyme, AvBD11...) also contributes to the antimicrobial defense of the developing embryo. Thus, VM plays a key role, not only in fertilization, but also during incubation. The present study aims at determining the protein composition of IVM and OVM to identify the intrinsic putative functions of each VM layer. IVM and OVM were manually separated from the VM of freshly-laid eggs and proteins from these two layers were independently solubilized, and analyzed by SDS-PAGE and GeLC-MS/MS. More than 550 proteins were identified with two peptides in the whole VM. Around 440 and 380 proteins were identified in IVM and OVM, respectively. Preliminary data resulting from the functional annotation of proteins (gene ontology/bibliography) revealed the presence of many proteins putatively associated with cell adhesion and migration, in addition to proteins involved in fertilization and antimicrobial defense. Altogether, the data generated from this study will give new insights into the structure and composition of the chicken egg VM and will provide an integrative overview of the respective physiological functions of IVM and OVM. Next, it will be interesting to further study how storage conditions prior to incubation may alter the structural/molecular integrity of IVM and OVM, and consequently negatively or positively impact the revival of embryonic development during incubation