Development and quality of bovine morulae cultured in serum-free medium with retinoic receptor specific agonists

Abstract

Retinoids regulate development and differentiation of the bovine blastocyst in vitro, although the underlying mechanisms remain to be clarified.Achallenge in reproductive biotechnology is the identification of pathways that regulate early embryonic development and their influence on blastocyst differentiation, apoptosis and survival to cryopreservation as traits of embryo quality. The present paper analyses the effects of short-term exposure (24 h) to retinoids on in vitroproduced bovine morulae. Immature cumulus oocyte complexes were in vitro matured and fertilised. Presumptive zygotes were subsequently cultured in modified synthetic oviduct fluid up to Day 6, in which morulae were randomly allocated to the different experimental groups. The treatments consisted of 0.1μm LG100268 (LG; a retinoid X receptor agonist), 0.7μm all-trans retinoic acid (ATRA; a retinoic acid receptor agonist) or no additives. Day 8 blastocyst development was increased in the ATRA-treated group compared with the LG and untreated embryos. In Day 7 embryos, the number of total cells and cells allocated to the trophectoderm were higher in the ATRA-treated group compared with untreated embryos. Apoptosis in the inner cell mass increased after LG treatment, whereas ATRA had no effect. After vitrification and warming, survival and hatching rates of Day 7 blastocysts did not change with retinoid treatment. Within the LGtreated and untreated blastocyst groups, survival and hatching rates were higher for Day 7 than Day 8 embryos; however, Day 8 blastocysts treated withATRA showed improved hatching rates. In conclusion, treatment of morulae withATRA in serum-free medium improves embryo development and quality without increasing the incidence of apoptosis and necrosis.