Proteomic ICM-MS profiling of single bovine oocytes and surrounding cumulus cells as a novel approach to access potential biomarkers of oocyte quality

Sessions WGII: Tools, Technologies, and Systems Biology.

International audience

anglais. Oocyte developmental competence is acquired throughout meiotic maturation which is accompanied by significant modifications of protein content both in oocyte and in surrounding cumulus cells (CC). We aimed to determine the proteins that reflect the oocyte capacity to develop to the embryo, i.e. oocyte quality. Classical differential proteomic analysis of oocytes and CC is limited due to the scarcity of such material. We adapted Intact Cells Matrix-Assisted Laser Desorption /Ionisation time-of-flight Mass Spectrometry (ICM-MS) to analyze individual oocytes and small amounts of CC in order to achieve direct protein/peptide profiling of these cells. Mass spectra gathering peaks in 3000-30000 mlz range were obtained for a number of single oocytes and CC biopsies without protein extraction by using MALDI-TOF with positive linear mode. After processing, for each m/z species their normalized peak heights were compared between different oocyte and CC groups and ANOVA p-value was calculated (Progenesis-MALDI). 113 and 168 m/z peaks_were reproducibly detected in oocytes and CC, respectively. Among them, intensity of 24 and 41 peaks varied (p<O.OS) in immature vs. mature oocytes and CC, respectively. Sets of changing peaks were determined through consecutive stages of oocyte meiotic maturation (GV, GVBD, Metaphase-I, Anaphase-I, Metaphase-II), and they could distinguish these stages by Principle Component Analysis (PCA). Moreover, several peaks seem to reflect oocyte quality when different models of competence were compared (in vivo vs. in vitro maturation, adult vs. prepubertal animals). In cumulus cell, ICM-MS was used to look for non-invasive biomarkers reflecting the capacity of individual oocyte to develop to blastocyst after in vitro fertilization. PCA performed on varying peaks in CC that enclosed the oocytes that developed or not to blastocyst was able to discriminate these groups. Identification of the proteins that gave rise to changing m/z species is the next challenge to characterize biomarqueurs of oocyte quality.