SEASONAL EFFECTS ON EPIGENETIC MACHINERY GENE EXPRESSION IN BOVINE OOCYTE

BARRIONUEVO MG; CORIA MS; REINERI PS; DI LULLO D; LUNA BE; RIVERO MB; ABDALA ME; LUQUE ME; RIVERO FD; CARRANZA PG; PALMA GA

Buenos Aires

Congreso; XVIII ANNUAL MEETING OF THE ARGENTINE BIOLOGY SOCIETY; 2016

ARGENTINE BIOLOGY SOCIETY

Santiago del Estero became in one of the regions most important livestock production in Argentina. In this region predominate very high temperatures which often exceed 40°C in the summer. Mammalian oocytes acquire their meiotic competence and fertilization potential in a stepwise manner. As a result, they are potentially exposed to various environmental stressors during follicular development. During oogenesis, epigenetic modifications are established which are required for normal embryonic progression. DNA methylation is the archetypal epigenetic mark. In the oocyte, an overall increase in global DNA methylation occur during the growth phase. In this study, we examined the association between seasons and expression of genes playing an essential role as part of epigenetic machinery in immature bovine oocyte. We analyzed the expression levels of DNA methyltransferases DNMT1, DNMT3a and DNMT3b; demethylase TET3 and STELLA, a maternal factor that protect the genome from active DNA demethylation that occurs soon after fertilization. Also, we examinated the expression of PRDX1 involved in oxidative stress response, heat shock protein 70 (HSP70), BMP15 and GDF9. Bovine ovaries were obtained from a local abattoir from Braford cows during the summer (jan-feb) and winter (jun-jul) seasons. Cumulus?oocyte complexes (COCs) were aspirated from 3 to 8 mm follicles. The oocytes were pipetted vigorously to ensure that they were fully denuded. To determine cross-contamination we carried out a semi-quantitative PCR using marker genes for oocyte: ZAR, granulosa cells: CYP 19A1 and thecal cells: CYP 17A1. Real-time PCRs were carried out with GAPDH and 18S rRNA as reference genes. STELLA expression was lower in oocyte from cold season versus the hot season counterparts. Results show a tendency of lower DNMT3a mRNA level in winter. As long as TET3, DNMT1, DNMT3b and HSP70 expression had no significative differences. We found that GDF9 and BMP15 mRNA expression decrease in cold season versus hot season and PRDX show a tendency of lower expression in cold season. Taken together, these results suggest a deleterious seasonal effect on gene expression of epigenetic machinery and oocyte developmental competence.