173 THE EFFECT OF AMINO ACIDS AND HYALURONAN ON BOVINE EMBRYO IN VITRO DEVELOPMENT AND GENE EXPRESSION PATTERN

Abstract

We have previously shown that bovine embryos cultured in SOFaa (BME + MEM amino acids) culture medium with hyaluronan (HA) + BSA are of better quality (Gutiérrez-Adán et al. 2005 Reprod. Fertil. Dev. 17, 219). Our objective was to examine the effect of essential (BME) or non-essential (MEM) amino acids with or without HA (MAP-5; Bioniche, Inc., Belleville, Ontario, Canada) on bovine embryo in vitro development and mRNA transcription of five developmentally important genes; apoptosis (Bax), growth factor (IGF-II), glucose (Glut-1) and fructose (Glut-5) transport and metabolism, and cell to cell adhesion (Cx-43). A total of 1474 presumptive zygotes (5 replicates) were initially cultured in 40 µL drops in the following groups: Group 1, control, SOFaa; Group 2, SOF-1 (MEM only); and Group 3, SOF-2 (BME only). On Day 4 (~96 h post-insemination (pi) the number of zygotes that had developed to d8 cells was recorded and 10 µL of SOF-1 and SOF-2, each with 2.5 mg/mL HA, was added to half of the embryos from Groups 2 and 3, respectively; the other half of Groups 2 and 3 and control group received 10 µL of corresponding medium without HA. Embryos were cultured 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. Five blastocysts from each replicate from each treatment were frozen for determination of gene expression patterns later. Cleavage rates and embryo development 96 h pi were compared among groups by chi-square analysis. The effects of HA and medium on blastocyst rates were analyzed by logistic regression and the data on mRNA expression by one-way repeated-measures ANOVA. Cleavage rates were 81.1% in SOFaa and 79.3% in SOF-1 (P = 0.48) and different from those in the SOF-2 group (72.4%; P < 0.02). The proportion of embryos that developed to d8 cells at Day 4 was higher in the control (46.7%) and SOF-1 (46.8%) groups than in the SOF-2 group (32.6%). The number of blastocysts that developed in SOFaa (37.0%), SOF-1 (37.7%), and SOF-1 + HA (37.8%) were higher (P < 0.001) than those in SOF-2 (19.6%) and SOF-2 + HA (21.8%). The level of expression of Glut-5 was not different among the groups. However, SOF-2 was the only group that had significantly lower expression of Glut-5, Igf II, and Cx43, and higher expression of BAX (P < 0.05) as compared to the control group and the SOF-1 groups with or without HA. Addition of HA to SOF-2 medium increased expression of Glut-1 and Igf II and decreased expression of BAX as compared to the SOF-1 only and control groups and the SOF-2 groups with or without HA (P < 0.05). The level of expression of Cx43 was higher in the control than in four remaining groups, and lower in the SOF-2 than in the SOF-1 group (P < 0.05). Addition of HA increased expression of Cx43 in both SOF-1 and SOF-2 groups but this level of expression was lower than in the control group; the level in the SOF-2 + HA group was lower (P < 0.05) than in the SOF-1 + HA group. We conclude that, within our protocol, MEM amino acids only stimulate embryo development to the blastocyst stage and the addition of HA to the SOF-MEM and SOF-BME media on Day 4 of culture improved embryo quality.