138 THE EFFECT OF SYNTHETIC HYALURONAN, BSA AND SERUM ON IN VITRO DEVELOPMENT AND GENE TRANSCRIPTION OF BOVINE BLASTOCYSTS

Abstract

The objective of this study was to examine the effect of synthetic hyaluronan (s-HA), BSA and fetal calf serum (FCS) on bovine embryo in vitro development, ultrastructure, and mRNA transcription of four developmentally important genes: apoptosis (BAX), oxidative stress (SOX), growth factor (IGF-II), and cell-to-cell adhesion (Ecad). A total of 1406 presumptive zygotes (7 replicates) were cultured initially in two Groups: 1, SOFaa + 4% BSA only, and 2, SOFaa + 4% BSA and 10% FCS. On Day 4 (96 h after insemination) of culture, the number of zygotes that developed to the <8-cell-stage were recorded, and 2.5 mg/mL of s-HA (MAP-5; Bioniche Inc, Belleville, ON, Canada) was added to half of the embryos from each group; the other half received an equivalent volume of corresponding SOF medium without s-HA. Embryos were cultured in 50-μL drops (25 zygotes per drop) under paraffin oil at 39°C and 5% CO₂ in humidified air. Cleavage rates were recorded on Day 2 and the number of blastocysts on Days 7, 8, and 9. At least five blastocysts from each replicate and from each treatment were frozen for evaluation of gene expression patterns. Poly(A) mRNA was prepared from 4–5 groups of pools of 10 embryos. The quantification of all gene transcripts was performed by real time quantitative RT-PCR in three replicates. The fine structure of blastocysts was studied using transmission electron microscopy. Embryo developmental stages and blastocyst formation were analyzed by chi-square analysis, and data on mRNA expression were analyzed by one-way repeated-measures ANOVA. No differences in cleavage rates were observed between groups. There was no difference between the BSA group with or without s-HA in the percentages of embryos developed to the blastocyst stage at Days 7, 8, and 9 (38.3 and 38.1%, respectively). However, significantly (P < 0.05) less blastocysts developed in medium supplemented with BSA + FCS (18.3%) or with BSA + FCS + s-HA (27.4%). Synthetic HA added to the medium containing BSA significantly (P < 0.05) increased the level of expression of EGF-II and decreased (P < 0.05) the level of expression of BAX, SOX, and Ecad. On the other hand, presence of FCS significantly (P < 0.05) increased the level of SOX and decreased the level of IGF-II (P < 0.05), and the addition of s-HA to SOF containing FCS showed no effect on the level of transcription of any analyzed genes. The general fine structure of embryos cultured with s-HA regardless of protein supplement was conspicuously improved in comparison with the respective controls. It can be concluded that, within our culture system, addition of s-HA on Day 4 of culture to the SOFaa medium supplemented with BSA but not in combination with FCS showed a positive effect on embryo development and molecular composition of the embryos.