Maturational competence of equine oocytes is associated with alterations in their "cumulome".

Abstract

Assisted reproductive technologies are an emerging field in equine reproduction, with species dependent peculiarities, such as the low success rate of conventional in vitro fertilisation. Here, the "cumulome" was related to the developmental capacity of its corresponding oocyte. Cumulus oocyte complexes (COCs) collected from slaughterhouse ovaries were individually matured, fertilised by intracytoplasmic sperm injection (ICSI), and cultured. After maturation, the cumulus was collected for proteomics analysis using label-free mass spectrometry (MS) based protein profiling by nano-HPLC MS/MS and metabolomics analysis by UPLC-nanoESI MS. Overall, a total of 1671 proteins and 612 metabolites were included in the quantifiable "cumulome". According to the development of the corresponding oocytes, three groups were compared with each other: not matured (NM; n = 18), cleaved (CV; n = 15) and blastocyst (BL; n = 19) groups. CV and BL were also analysed together as the matured group (M; n = 34). The dataset revealed a closer connection within the two M groups and a more distinct separation from the NM group. Over-representation analysis detected enrichments related to energy metabolism as well as vesicular transport in the M group. Functional enrichment analysis found only the KEGG pathway of oxidative phosphorylation as significantly enriched in NM group. A compound attributed to ATP was observed with significantly higher concentrations in the BL group compared with the NM group. Finally, in the NM group, proteins related to degradation of glycosaminoglycans were lower and components of cumulus extracellular matrix were higher compared to the other groups. In summary, the study revealed novel pathways associated with the maturational and developmental competence of oocytes.