Proteomics reveals substantial differences between in vitro matured abattoir-derived and in vivo matured oocytes in cattle

In vitro production (IVP) of bovine embryos still has its limitations, such as low blastocyst rate and lower embryo quality, resulting in lower pregnancy rates following transfer compared to in vivo produced embryos. Transcriptional studies comparing both types of embryos mainly utilized oocytes retrieved from slaughterhouse material for IVP, thereby introducing the possibility, that differences between IVP and in vivo embryos are in part attributable to differing sources of oocytes. The aim of the present study was therefore to compare the proteome of oocytes retrieved from slaughterhouse material, with and without a period of in vitro maturation, and in vivo matured oocytes obtained from superovulated donor cattle. For each group the protein pattern of four technical replicates containing ten oocytes each were analyzed via SWATH™-MS. In total, 1208 proteins were detected, 160 of which were differentially abundant in at least one group comparisons. Clustering analysis revealed that oocyte maturation environment is the primary driver of molecular difference, with the in vitro matured oocytes exhibiting a highly distinct proteome compared to both the in vivo matured and immature oocytes. In vitro matured oocytes were characterized by an overall enhanced translational activity affecting mainly proteins involved in energy metabolism, transcription and translation, and oocyte activation. An organized regulation of key pathways was observed during oocyte maturation in vivo, e.g. activation of autophagy and apoptosis pathways, while changes in protein abundance in vitro seem to be undirected. This deregulation of the proteome in in vitro matured oocytes likely negatively affect subsequent developmental events.