232 EFFECT OF MEIOTIC ARREST USING BUTYROLACTONE I AND ROSCOVITINE ON IN VITRO PRODUCTION OF BOVINE EMBRYOS

Abstract

Butyrolactone I (BL-I) and roscovitine (ROS) are selective inhibitors of the cyclin-dependent kinases, and both have been shown to reversibly inhibit meiotic resumption in cattle oocytes without having a negative effect on subsequent development to the blastocyst stage. The aim of this study was to evaluate the in vitro production of bovine embryos in the presence of BL-I (Enzo Life Sciences International Inc., Plymouth Meeting, PA, USA) and ROS (Sigma-Aldrich, St. Louis, MO, USA). For that, Nellore oocytes were matured in TCM-199 with Earle’s salts + 10% FCS, FSH, and LH, in a 5% CO₂ atmosphere. To delay meiosis, the oocytes were maintained for 6 h in medium in the presence of 25 µM BL-I + 6.25 µM ROS. The oocytes were then cultured for 18 h in agent-free medium to resume meiosis, completing 24 h of maturation. After 24 h of maturation (Day 0), oocytes were fertilized in human tubal fluid (HTF, Irvine, New Zealand), in a 5% CO₂ atmosphere. Semen was selected through Percoll gradient and the concentration was adjusted to 2 × 10⁶ sperm mL^–1. The presumed zygotes were cultured inside a bag in 90-µL droplets of SOFaa + 0.6% BSA + 2.5% FCS in a 5% CO₂, 5% O₂, and 90% N₂ atmosphere until Day 7, when blastocyst rate was evaluated. Five replicates were done. Data were analysed with ANOVA, followed by Tukey’s test using the general linear models procedure (PROC GLM) of SAS, version 9.2 (SAS Institute Inc., Cary, NC, USA). The level of significance adopted was 5%. No statistical differences were observed in blastocyst production rate: control, 33.3 ± 3.74%; BL-I + ROS, 38.0 ± 4.5%. Thus, the presence of BL-I + ROS in the prematuration medium of bovine oocytes did not compromise their subsequent developmental competence. The next steps of the present study are evaluating the kinetics of blastocyst formation and detecting apoptotic cells in situ by TUNEL, which will show that these substances do not compromise embryonic quality.