307 MATURATION RATE AND GENE EXPRESSION ANALYSIS OF GOAT OOCYTES SELECTED BY FOLLICLE SIZE AND BRILLIANT CRESYL BLUE STAINING

Abstract

Oocyte quality plays a critical role in determining the success of embryo development. Studies on cattle and goats indicate that oocytes derived from large follicles (LFO) have greater developmental competence than those derived from small follicles (SFO). Brilliant cresyl blue (BCB) staining determines the activity of glucose-6-phosphate dehydrogenase and is a commonly used noninvasive marker of oocyte competence. Studies in pigs, goats, cows, mice, and dogs showed that the maturation and blastocyst developmental rate of BCB+ oocytes is significantly higher than BCB– oocytes. The aim of this study was to evaluate the maturation rate of goat oocytes selected based on follicular size and BCB staining and compare their relative patterns of gene expression. Maturation rate and gene expression profile were expected to be different in these oocyte groups. Cumulus-oocyte complexes were recovered from abattoir-derived ovaries using a slicing technique. Eleven rounds of oocyte maturation and 4 rounds of BCB staining were carried out. During each replicate, oocytes from large (≥3 mm) and small (<3 mm) follicles were collected separately from the same group of ovaries. Oocyte maturation rates were 54.3 ± 5.4% for LFO (n = 378) and only 33.5 ± 3.7% for SFO (n = 981; P < 0.01). The BCB+ (n = 223) oocytes yielded a significantly higher maturation rate than the BCB– (n = 194) oocytes (56.1 ± 1.8 v. 20.6 ± 3.8%, respectively; P < 0.001). Gene expression analysis was conducted on individual MII oocytes (21 oocytes per group). Specific target amplification was performed on a single oocyte directly by using the CellsDirect One-Step qRT–PCR Kit (Invitrogen). Quantitative real-time PCR was then performed using the 48.48 BioMark platform from Fluidigm. Forty two genes were selected from the following categories: growth factors, transcription factors, metabolism, pluripotency, cell cycle, apoptosis, and oocyte-specific genes. Relative expression values were calculated using the ΔΔCT (fold change) method and analysed by ANOVA. The significance was assigned at P < 0.05. The relative expression of CCNA2, CDK2, CCNB1, POU5F1, SOX2, EGF, FGF2, GDF9, ZP3, BCL2, GJA1, DDR1, PFKFB3, IGF2R, and GRB10 was significantly greater (P < 0.05) in both LFO and BCB+ oocytes compared to SFO and BCB– oocytes, respectively. The proapoptotic gene BAX, the ACSL3 gene involved in fatty acid oxidation, and the growth factor IGF1 were expressed significantly higher (P < 0.05) in SFO compared to LFO. By investigating these differentially expressed transcripts, we will better understand pathways involved in oocyte developmental competence and potentially use them as markers of oocyte quality. We expect that the ability to select oocytes of better quality based on BCB staining will improve outcomes of IVF and SCNT.