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Title: Comparative Proteomic and Regulatory Network Analyses of the Elongating Pig Conceptus

item Blomberg, Le Ann
item Garrett, Wesley
item Li, Robert
item Talbot, Neil

Submitted to: Proteomics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/13/2009
Publication Date: 5/1/2009
Citation: Degrelle, S.A., Blomberg, L., Garrett, W.M., Li, R.W., Talbot, N.C. 2009. Comparative Proteomic and Regulatory Network Analyses of the Elongating Pig Conceptus. Proteomics. 9(10):2678-94.

Interpretive Summary: Pork continues to be an important large animal commodity world-wide. However, despite the selection of animals with improved reproductive traits, the efficiency of swine production is still hindered by high embryo loss. Multiple studies have attempted to elucidate the physiology regulating competent embryo by in-depth gene expression studies of messenger RNA (mRNA) from embryos during the greatest period of embryonic loss; a period occurring just prior to implantation and accompanied by a rapid change in embryo shape (elongation). However, a constant underlying criticism for transcriptomic studies has often been that mRNA expression might not truly reflect the expression profile of the factors, proteins, with biological activity. Considering the central physiological and structural roles of proteins, a study was undertaken using mass spectrometry (MS) methodologies for an in-depth examination of the porcine embryo’s intracellular protein expression profile at the beginning and end of elongation. Aside from 174 unique proteins that were identified, differential expression of proteins involved in implantation, morphogenesis, and structure/reorganization of the embryo was detected between the two distinct embryonic stages. Furthermore, stage-specific post-translational modifications of potential biological significance were found for several proteins in the embryo. A comparison of protein and mRNA levels indicated that mRNA can be detected for about 50% of the abundant proteins present in the embryo and of the most abundant proteins (top 10%) identified, the mRNA and protein expression profiles were similar for approximately 60% of the genes. In addition, only 1/3 of the abundant proteins could be considered abundant mRNAs. This work has enabled a first glimpse of the intracellular protein repertoire of the porcine embryo and the establishment of a protein reference map for specific stages during elongation. In addition, it has provided some insight into the maintenance and deviations in the expression of some potentially important developmental factors at two distinct levels, mRNA and protein.

Technical Abstract: Embryo loss during peri-implantation can approach 20% in swine following artificial insemination or natural mating and coincides with rapid embryo elongation. The objective of the present study was to establish a comprehensive profile of the pig embryo’s abundant proteins at the time prior to implantation and identify stage-specific changes during elongation. The abundant proteins of a homogenous population of gestational day-11 ovoid (0.7-1cm) and gestational day-12 filamentous (15-20 cm) porcine concepti were compared by extracting proteins from three independent embryo pools and separating the proteins by 2-DE gel electrophoresis. Proteins in 305 spots were analyzed by matrix-assisted laser desorption/ionization time of flight spectrometry and tandem liquid chromatography-mass spectrometry and 274 were positively identified representing 175 distinct proteins. The proteins could be classified into the following functional categories: cell proliferation/differentiation, cytoskeleton, metabolism, and stress response. Based on spot density, 37 proteins associated with cell proliferation, differentiation, apoptosis and embryo/maternal signaling, were found to be differentially expressed between ovoid and filamentous concepti. A comparison of the protein expression profile with transcriptomic data from pig concepti of the same developmental stages identified similarities and dissimilarities between protein and mRNA expression profiles. This proteomic study helps to elucidate the biological mechanisms underlying the early embryonic development of the pig.