Embryology in the era of proteomics.

Currently, relatively little is known regarding the protein production of mammalian embryos. Unlike the genome, the proteome itself is dynamic reflecting both internal and external environmental stimuli. Until now the lack of sensitivity has remained a stumbling block for the global introduction of proteomics into the field of mammalian embryology. However, new developments in mass spectrometry have been revolutionary, utilizing protein profiling and peptide sequencing to elucidate underlying biological processes. The sensitivity of these platforms have allowed for the development of new protocols that are capable of profiling the proteome of individual mammalian oocytes and embryos. This information is fundamental to unravelling the complexity of embryo physiology including the dialogue between the developing embryo and its maternal environment. Such proteomic approaches are also assisting in the optimization of ART techniques, including oocyte cryopreservation and in vitro maturation. Embryo selection for transfer is another area of ART that should benefit in this era of proteomics. Currently, mammalian embryos are selected for transfer based on morphological grading systems. Although of great value, analysis of morphology alone cannot determine the embryo's physiological state or chromosomal complement. Subsequently, there is a need to identify in culture those embryos with the highest implantation potential. Proteomic analysis of the embryonic secretome (proteins produced by the embryo and secreted into the surrounding medium) followed by the identification of specific proteins critical for implantation, may lead to the development of a non-invasive viability assay to assist in the selection of embryos for transfer.