Development of in vitro derived bovine embryos following pronuclear transplantation and in vitro culture.

This study was designed to evaluate the survival and development of in vitro derived bovine embryos following pronuclear transplantation and in vitro embryo culture. Bovine zygotes were produced by in vitro maturation and in vitro fertilization. Pronuclei were removed by micromanipulation and either transferred back to the same cell (Group 1) or into a previously enucleated zygote (Group 2) by electrofusion. Micromanipulated and non-micromanipulated (Group 3, control) zygotes were co-cultured with oviductal cells in a sealed modular chamber filled with 5% CO2, 5% O2 and 90% N2 at 39 degrees C for 7-8 days. Fusion rates were similar for Groups 1 and 2 (90.7 and 85.1%, respectively, P > 0.05). The percentage of embryos that cleaved was not different for Groups 1 (82.0%), 2 (90.0%) and 3 (76.9%, P > 0.05). Also, the percentage of embryos developing to the compact morula or blastocyst stage was similar (25.6, 22.5 and 22.3%, respectively, for Groups 1, 2 and 3, P > 0.05). The results of this experiment are the first to demonstrate that pronuclear transfer can be carried out successfully using bovine embryos derived from in vitro oocyte maturation and in vitro fertilization. In addition, pronuclei can be transferred from one bovine embryo to another and the reconstructed embryos develop to the compact morula and blastocyst stage in vitro. This technique, used in combination with oocyte retrieval by ultrasound-guided follicular aspiration and embryo transfer, offers the potential to study cytoplasmic inheritance in cattle directly, and to evaluate the effect of cytoplasmic inheritance on traits of economic importance.