Identification of molecular markers for oocyte competence in bovine cumulus cells.

Cumulus cells (CCs) have an important role during oocyte growth, competence acquisition, maturation, ovulation and fertilization. In an attempt to isolate potential biomarkers for bovine in vitro fertilization, we identified genes differentially expressed in bovine CCs from oocytes with different competence statuses, through microarray analysis. The model of follicle size, in which competent cumulus-oocyte complexes (COCs) were recovered from bigger follicles (≥8.0 mm in diameter) and less competent ones from smaller follicles (1-3 mm), was used. We identified 4178 genes that were differentially expressed (P < 0.05) in the two categories of CCs. The list was further enriched, through the use of a 2.5-fold change in gene expression as a cutoff value, to include 143 up-regulated and 80 down-regulated genes in CCs of competent COCs compared to incompetent COCs. These genes were screened according to their cellular roles, most of which were related to cell cycle, DNA repair, energy metabolism, metabolism of amino acids, cell signaling, meiosis, ovulation and inflammation. Three candidate genes up-regulated (FGF11, IGFBP4, SPRY1) and three down-regulated (ARHGAP22, COL18A1 and GPC4) in CCs from COCs of big follicles (≥8.1 mm) were selected for qPCR analysis. The selected genes showed the same expression patterns by qPCR and microarray analysis. These genes may be potential genetic markers that predict oocyte competence in in vitro fertilization routines.

Transcription profile of candidate genes for the acquisition of competence during oocyte growth in cattle.

The aim of this study was to investigate the expression profile of candidate genes involved in competence during oocyte growth. The candidate genes (BMP15, OOSP1, H1FOO, H2A, H3A, H4, SLBP, DNMT1, DNMT3B, HAT1, HDAC2 and SUV39H1) were selected because of their possible involvement in determining oocyte developmental competence. Pre-antral and antral follicles were isolated from the ovaries of Zebu (Bos indicus) cows, measured and classified into the following categories according to their diameter: (i) oocytes from primordial follicles: diameter <20 µm, (ii) oocytes from primary follicles: 25-35 µm, (iii) oocytes from small secondary follicles: 40-60 µm, (iv) oocytes from large secondary follicles: 65-85 µm, (v) oocytes from small antral follicles: 100-120 µm, and (vi) oocytes from large antral follicles: >128 µm. Total RNA was extracted from four pools of 25 oocytes for each category of follicles, and the genes were quantified by qPCR. Target gene expression was normalized using the gene PPIA. The results suggest that stocks of the studied transcript genes accumulate before the final phase of folliculogenesis. The HDAC2 gene was the only gene in which a differential expression was observed at stage associated with competence acquisition.