184 EFFECT OF HISTONE DEACETYLASE INHIBITOR ON DEVELOPMENT OF EMBRYOS DERIVED FROM HEAT-SHOCKED BOVINE OOCYTES

Abstract

Heat shock affects the oocyte developmental competence and embryonic gene expression. We found that the chromatin organisation of embryos derived from heat-shocked oocytes can also be affected (Camargo et al. 2015 Reprod. Fert. Dev. 27, 132). This study aimed to evaluate whether Scriptaid, a histone deacetylase inhibitor able to modulate the chromatin structure, could influence the development of embryos derived from heat-shocked oocytes. Bovine oocytes were in vitro-matured under conventional temperature (38.5°C) for 24 h (non-heat-shock; NHS group) or under 41.5°C for 12 h followed by 38.5°C for 12 h (heat-shock; HS group). In vitro fertilization was performed under 38.5°C with 5% CO₂ in air for 20 h. Right after the end of fertilization the presumptive zygotes from the NHS or HS groups were denuded and randomly exposed to 500 nM Scriptaid for 0, 12, or 24 h, comprising 6 treatments as followa: NHS-0 h (NHS without Scriptaid, n = 185); NHS-12 h (NHS plus Scriptaid for 12 h, n = 178); NHS-24 h (NHS plus Scriptaid for 24 h, n = 177); HS-0 h (HS without Scriptaid, n = 187); HS-12 h (HS plus Scriptaid for 12 h, n = 180); and HS-24 h (HS plus Scriptaid for 24 h, n = 183). After Scriptaid exposure, zygotes were cultured in CR2aa plus 2.5% FCS at 38.5°C with 5% CO₂, 5% O₂, and 90% N₂. Cleavage rate was calculated on Day 2 (44 h post-fertilization) and blastocyst rates on Day 7 and 8 post-fertilization. Six replicates were carried out and data was analysed by logistic regression (Proc Logistic, SAS 9.2, SAS Institute Inc., Cary, NC). Significant data were interpreted as odd ratios considering the 95% confidence interval. Values are shown as mean ± standard error of the mean. There was no difference (P > 0.05) among NHS treatments (NHS-0 h, NHS-12 h, and NHS-24 h) as well as among HS treatments (HS-0 h, HS-12 h, and HS-24 h) for cleavage and blastocyst rates at Day 7. At Day 8, however, the blastocyst rate in the NHS group decreased (P < 0.05) as the time of zygote exposure to Scriptaid increased to 24 h (33.9 ± 2.8 and 24.2 ± 1.6% for NHS-0 h and NHS-24 h, respectively), whereas no difference (P > 0.05) was found in the HS group (20.7 ± 1.5, 21.2 ± 1.6, and 20.5 ± 2.4% for HS-0 h, HS-12 h, and HS-24 h, respectively). Comparison between NHS and HS treatments showed that cleavage and blastocyst rates at Day 7 and 8 of NHS-0 h (88.7 ± 2.8, 30.1 ± 1.5, and 33.9 ± 2.8%, respectively) were superior (P < 0.05) to HS-0 h (79.3 ± 3.2, 16.9 ± 1.0, and 20.7 ± 1.5%, respectively). Differences (P < 0.05) between NHS-12 h and HS-12 h on blastocyst rates at Day 7 (32.8 ± 3.8 v. 20.6 ± 1.7%, respectively) and at Day 8 (31.7 ± 2.7 v. 21.2 ± 1.6%, respectively) were also found. However, no difference (P > 0.05) between NHS-24 h and HS-24 h was found. We showed that Scriptaid for 24 h right after IVF has a negative impact on further development of zygotes derived from oocytes matured under conventional temperature (NHS group), in contrast to zygotes derived from oocytes matured under high temperature (HS group). We concluded that the effect of Scriptaid on embryo development is influenced by the temperature during oocyte maturation.

Supported by FAPEMIG, CAPES, and CNPq.