Proteomic analysis of germinal vesicles in the domestic cat model reveals candidate nuclear proteins involved in oocyte competence acquisition

STUDY QUESTION: Do nuclear proteins in the germinal vesicle (GV) contribute to oocyte competence acquisition during folliculogenesis? SUMMARY ANSWER: Proteomic analysis of GVs identified candidate proteins for oocyte competence acquisition, including a key RNA processing protein-heterogeneous nuclear ribonucleoprotein A2/B1 (hnRNPA2B1). WHAT IS KNOWN ALREADY: The domestic cat GV, which is physiologically similar to the human GV, gains the intrinsic ability to resume meiosis and support early embryo development during the pre-antral-to-antral follicle transition. However, little is known about nuclear proteins that contribute to this developmental process. STUDY DESIGN SIZE, DURATION: GVs were enriched from pre-antral (incompetent) and antral (competent) follicles from 802 cat ovaries. Protein lysates were subjected to quantitative proteomic analysis to identify differentially expressed proteins in GVs from the two follicular categories. PARTICIPANTS/MATERIALS, SETTING, METHODS: Two biological replicates (from independent pools of ovaries) of pre-antral versus antral samples were labeled by tandem mass tags and then assessed by liquid chromatography-tandem mass spectrometry. Proteomic data were analyzed according to gene ontology and a protein-protein interaction network. Immunofluorescent staining and protein inhibition assays were used for validation. MAIN RESULTS AND THE ROLE OF CHANCE: A total of 174 nuclear proteins was identified, with 54 being up-regulated and 22 down-regulated (>= 1.5-fold) after antrum formation. Functional protein analysis through gene ontology over-representation tests revealed that changes in molecular network within the GVs during this transitional phase were related to chromatin reorganization, gene transcription, and maternal RNA processing and storage. Protein inhibition assays verified that hnRNPA2B1, a key nuclear protein identified, was required for oocyte meiotic maturation and subsequent blastocyst formation. LARGE SCALE DATA: Data are available via ProteomeXchange with identifier PXD007211. LIMITATIONS REASONS FOR CAUTION: Proteins identified by proteomic comparison may (i) be involved in processes other than competence acquisition during the pre-antral-to-antral transition or (ii) be co-expressed in other macrostructures besides the GV. Expressional and functional validations should be performed for candidate proteins before downstream application. WIDER IMPLICATIONS OF THE FINDINGS: Collective results generated a blueprint to better understand the molecular mechanisms involved in GV competence acquisition and identified potential nuclear competence markers for human fertility preservation.