76 EFFECT OF CULTURE METHOD ON THE mRNA EXPRESSION BEFORE AND AFTER CRYOPRESERVATION IN BOVINE BLASTOCYSTS

Abstract

Blastocyst mRNA expression and cryopreservability are thought to be suitable indicators of embryo quality and developmental competence and have been shown to be affected by production methods and culture systems. The aim of the present study was to assess cryosurvival and levels of mRNA expression of selected genes [occludin, desmocollin 2, solute carrier family 2 member 3 (formerly glucose transporter 3), BAX, BCL xL, heat shock protein A1A (formerly heat shock protein 70.1), aquaporin 3, and DNA methyltransferase 1a] of bovine blastocysts derived by 4 different, established culture methods [in vitro production (IVP); multiple-ovulation embryo transfer (MOET); transfer into the heifer oviducts of gametes (GIFT); or in vitro derived cleaved stage embryos (Days 2–7)]. Linear models were used for the comparison of the relative abundances of the blastocyst mRNA transcripts. Separate 1-way ANOVA were used. The production methods were used as factors, except for the comparisons between pre- and post-cryopreservation, where 2-way ANOVA were used. The level of significance was set at P ≤ 0.05. A significant difference in re-expansion rates was found only at 24 h post-thawing, with significantly higher rates in blastocysts produced in vitro compared to embryos of the Days 2–7 group. Levels of mRNA expression were assessed using RT-qPCR. Before cryopreservation of embryos, no significant inter-group differences were seen. However, significantly more desmocollin 2 mRNA expression was detected in embryos of the MOET group compared with blastocysts derived by the other production methods. Post-cryopreservation, blastocysts of 3 embryo production groups (IVP, MOET, Days 2–7) were available for analysis. Compared with levels of mRNA expression before cryopreservation, re-expanded blastocysts after cryopreservation showed a significant up-regulation of heat shock protein A1A transcripts in all groups, and of solute carrier family 2 member 3 transcripts only in the IVP-derived group. The BAX, BCL-xL, occludin, and desmocollin 2 were significantly up-regulated in embryos of the MOET and IVP groups after cryopreservation, as compared with their counterparts before cryopreservation. None of the culture groups showed any pre- v. post-cryopreservation differences in the aquaporin 3 and the DNA methyltransferase 1 mRNA levels. Blastocysts derived by transfer of in vitro derived cleaved stage embryos into the oviduct of synchronised heifers (Days 2–7) did not show any pre- v. post-cryopreservation differences in the mRNA levels of any of the assessed genes. These results merit further investigation. After the process of cryopreservation and thawing, re-expanded embryos of the MOET and IVP groups do increase their mRNA levels to prepare for hatching and further development.