Characterization and quantification of proteins secreted by single human embryos prior to implantation.
Bottom Line: By using targeted proteomics, we demonstrate the feasibility of quantifying multiple proteins in samples derived from single blastocoels and that such measurements correlate with aspects of embryo viability, such as chromosomal (ploidy) status.This study illustrates the potential of high-sensitivity proteomics to measure clinically relevant biomarkers in minute samples and, more specifically, suggests that key aspects of embryo competence could be measured using a proteomic-based strategy, with negligible risk of harm to the living embryo.Our work paves the way for the development of "next-generation" embryo competence assessment strategies, based on functional proteomics.
Affiliation: Nuffield Department of Obstetrics and Gynaecology, Institute of Reproductive Sciences University of Oxford, Oxford, UK Oxford Fertility Unit, Institute of Reproductive Sciences, Oxford, UK Reprogenetics UK, Institute of Reproductive Sciences, Oxford, UK.Show MeSH
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Mentions: The expressed transcripts were then cross-referenced (Materials and Methods) with the catalog of proteins identified using urea-based or MonoPrep tandem mass spectrometry blastosol analysis. Data show that 123 out of 150 (82.0%) proteins identified with Mono-Prep preparations were actively transcribed in the embryo, while for urea-based samples, only 80 out of 169 (47.3%) were confirmed by microarrays (Fig2A). Thirty-one proteins (10.8%) were identified in both urea and MonoPrep groups. Of these identifications, 21 (67.7%) were confirmed by gene expression analysis, while 10 (32.3%) were unconfirmed. A statistical analysis of protein abundance for each group showed that shared proteins were not generally more abundant than those identified by a single method (see Materials and Methods for details). Also, proteins confirmed by microarrays were not more represented in the shared group compared to the sum total of all proteins identified (chi-square test, P-value = 0.697). A potential explanation for the higher validation rate of the MonoPrep samples is that this procedure is less prone to the introduction of contaminant proteins such as keratins (Table1). However, it is possible that some of the detected proteins that could not be confirmed by gene expression analysis were coded by maternal RNA, originally produced in the oocyte. The proteins may have been synthesized prior to fertilization or during the first few days of life, but persisted to the blastocyst stage. To investigate this possibility, we cross-checked the list of identified proteins that were not confirmed by microarray with current literature on human oocyte transcriptome (Kocabas et al, 2006). Only one protein (out of 106) of potential maternal origin was revealed (PSMA7, Proteasome subunit alpha, type 7). This does not exclude the possibility that other proteins of maternal origin may persist in the cells of blastocyst stage embryos, but clearly any such proteins are absent from the blastocoelic fluid (or below the threshold of detection).
Affiliation: Nuffield Department of Obstetrics and Gynaecology, Institute of Reproductive Sciences University of Oxford, Oxford, UK Oxford Fertility Unit, Institute of Reproductive Sciences, Oxford, UK Reprogenetics UK, Institute of Reproductive Sciences, Oxford, UK.