Stage-specific proteome signatures in early bovine embryo development.

Development of early embryonic stages before activation of the embryonic genome depends on sufficiently stored products of the maternal genome, adequate recruitment and degradation of mRNAs, as well as activation, deactivation, and relocation of proteins. By application of an isobaric tagging for relative and absolute quantification (iTRAQ)-based approach, the proteomes of bovine embryos at the zygote and 2-cell and 4-cell stage with MII oocytes as a reference were quantitatively analyzed. Of 1072 quantified proteins, 87 differed significantly in abundance between the four stages. The proteomes of 2-cell and 4-cell embryos differed most from the reference MII oocyte, and a considerable fraction of proteins continuously increased in abundance during the stages analyzed, despite a strongly attenuated rate of translation reported for this period. Bioinformatic analysis revealed particularly interesting proteins involved in the p53 pathway, lipid metabolism, and mitosis. Verification of iTRAQ results by targeted SRM (selected reaction monitoring) analysis revealed excellent agreement for all five proteins analyzed. By principal component analysis, SRM quantifications comprising a panel of only five proteins were shown to discriminate between all four developmental stages analyzed here. For future experiments, an expanded SRM protein panel will provide the potential to detect developmental disturbances with high sensitivity and enable first insights into the underlying molecular pathways.