Quantitative proteomics analysis of eggshell membrane proteins during chick embryonic development.

The avian eggshell membrane (ESM) is a meshwork made up of highly cross-linked protein fibers and it is a scaffold upon which biomineralization of the eggshell is initiated. The ESM and associated shell participates in embryonic development by providing physical and chemical protection against pathogen invasion. We performed quantitative proteomic analysis of ESM proteins on multiple days during the three phases of embryonic development. The ESMs were stripped from both fertilized and unfertilized eggs at different days of incubation, and solubilized in a novel manner using TCEP-HCl (Tris (2-carboxyethyl) phosphine hydrochloride). The changes in ESM proteins between occurred during incubation were analyzed. Bioinformatics analysis revealed that of the 12 functional protein clusters identified, protease inhibitors were present at all phases of chick development. A group of proteins involved in calcium binding and oxygen transport were only present during the second phase. Extracellular matrix, cell adhesion proteins related to the vascularization of chorioallantoic membrane (CAM), antimicrobial proteins and proteins involved in the binding and transport of lipids were found in the second and third phases of development. These findings provide insight into the functionality and evolving nature of ESM associated proteins involved in chick embryonic development. BIOLOGICAL SIGNIFICANCE: The eggshell membranes (ESMs) are a fibrous scaffold that consists of highly crosslinked collagens (types I, V but mainly X), glycoproteins and CREMPs (cysteine-rich eggshell membrane proteins). The ESMs aid in the development of the chick embryo and protect it against pathogen invasion. This biopolymeric fibrous net functions as a platform for nucleation of the calcitic eggshell which provides a primary physical barrier against bacterial ingress. Comparative proteomic analyses of proteins in the ESMs from fertilized eggs and unfertilized eggs showed changes in their levels which varied between the specific phases of chick embryogenesis across 19 days of incubation. Bioinformatics characterization of these ESM proteins provides understanding of their evolving nature during chick embryonic development.