Involvement of E-cadherin in early in vitro development of adult and juvenile sheep embryos.

The oocyte-to-embryo transition in mammals depends on maternal proteins and transcripts, which accumulate during oocyte differentiation. The aim of the present study was to examine the role of the junctional proteins beta-catenin and E-cadherin during preimplantation in vitro embryo development in sheep, comparing the competence of adult and prepubertal oocytes. We analysed the concentration of beta-catenin and E-cadherin in immature and in vitro-matured oocytes. There was a significant increase in E-cadherin concentration after 24 h of in vitro maturation and this was lower in prepubertal oocytes than in adult ones. We therefore studied the expression and distribution of E-cadherin during the major transition from maternal to embryonic genome. E-cadherin distribution and localisation in sheep was age- and developmental-stage dependent and was related to developmental kinetics. In fact, in adults, the majority of embryos showed the proper distribution of E-cadherin just beneath the membrane surfaces of all blastomeres and the percentage of embryos with this distribution increased with the increase in cell number during development. On the contrary, and regardless of their developmental stage, the majority of prepubertal embryos showed an uneven distribution of the protein, often associated with the occurrence of cellular fragmentation. In conclusion, our results suggest that E-cadherin plays a pivotal role during preimplantation embryo growth in sheep and may be one of the possible cytoplasmic factors involved in the reduced developmental competence of prepubertal female gametes.