Abstract
In vitro maturation (IVM) of oocytes has still a negative impact on the developmental competence of oocytes. Therefore, this study analysed the cumulus proteome of individual cumulus-oocyte complexes (COCs) with and without maturational competence, matured under in vivo or in vitro conditions (n = 5 per group). A novel, ultrasensitive mass spectrometry (MS) based protein profiling approach, using label-free quantification, was applied. The detected cumulus proteome included 2226 quantifiable proteins and was highly influenced by the maturation condition (479 differentially expressed proteins) as well as maturational competence of the corresponding oocyte (424 differentially expressed proteins). Enrichment analysis showed an overrepresentation of the complement and coagulation cascades (CCC), ECM-receptor interaction and steroid biosynthesis in cumulus of COCs that matured successfully under in vivo conditions. Verification of the origin of CCC proteins was achieved through detection of C3 secretion into the maturation medium, with significantly increasing concentrations from 12 (48.4 ng/ml) to 24 hours (68 ng/ml: p < 0.001). In relation, concentrations in follicular fluid, reflecting the in vivo situation, were >100x higher. In summary, this study identified important pathways that are impaired in IVM cumulus, as well as potential markers of the maturational competence of oocytes.
Highlights
In vitro maturation (IVM) of oocytes has still a negative impact on the developmental competence of oocytes
Increased rates of developmental abnormalities were described for in vitro produced embryos[13]. This might especially be the result of maturation in vitro, which results in a higher degree of chromosomal abnormalities and decreased cell counts per blastocyst[10]. All these findings suggest that the in vivo situation is not sufficiently reflected in in vitro maturation systems
Twenty cumulus samples corresponding to single oocytes were examined, using a mass spectrometry (MS) protein profiling approach
Summary
In vitro maturation (IVM) of oocytes has still a negative impact on the developmental competence of oocytes. This study analysed the cumulus proteome of individual cumulus-oocyte complexes (COCs) with and without maturational competence, matured under in vivo or in vitro conditions (n = 5 per group). For the in vitro production of embryos, this crucial step can still take place in vivo through hormonal stimulation of the oocyte donor These oocytes possess typically a higher developmental potential compared to their in vitro matured counterparts[1]. Despite high maturation rates of up to 90% of immature bovine oocytes under in vitro conditions, usually not more than 40% develop until the blastocyst stage[4,5,6,7,8] This is a substantially lower rate compared to the in vitro production of embryos from in vivo matured oocytes, for which a blastocyst rate of 73% was recorded[9]. Correlation of the cumulus proteome to the maturation stage of the corresponding oocyte might reveal potential biomarkers to predict the oocytes maturational competence
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