Activation of equine nuclear transfer oocytes: methods and timing of treatment in relation to nuclear remodeling.

This research investigates the most effective timing and methods to activate the process of nuclear transfer in horse cells in the context of developing embryos. The study found that the combination of 6-dimethylaminopurine (6-DMAP) with sperm extract improves the success rate of this process when compared to other methods.

Overview of the Research

• The study looked into the early development of embryos produced by the transfer of equine (horse) nuclei to bovine (cow) cytoplasts, the part of the cell that encompasses everything excluding the nucleus.
• The researchers found that inter-species nuclear transfer embryos (where equine nuclei was transferred to bovine cytoplasts) developed better when compared to intra-species nuclear transfer embryos (where the nuclei and cytoplasts were both from horses), suggesting the variation may be due to different chromatin remodeling or activation efficiency between the two types of oocytes.

Nuclear Remodeling Pattern

• The pattern of donor nucleus remodeling was examined in both equine-equine and equine-bovine reconstructed oocytes.
• Chromosome condensation, a key part of chromatin remodeling, occurred in equine cytoplasts within 2 hours, but the same did not happen in bovine cytoplasts until 4 hours post reconstruction.

Effect of Activation Time on Outcomes

• The team also investigated the impact of different timings of activation on these reconstructed oocytes, focusing on activations that occurred at less than 30 minutes and at 2 hours after the reconstruction.
• They tested four activation methods: the use of sperm extract alone or in combination with 6-DMAP, cytochalasin B, or 1% dimethylsulphoxide.
• No significant difference was found between activating the oocytes at less than 30 minutes or 2 hours after the reconstruction process in terms of average nucleus count or rate of normal cleavage of embryos.

Best Activation Methods

• Of the activation methods tested, the combination of 6-DMAP with sperm extract significantly improved the cleavage rate compared to the other three treatments.
• When activation was carried out with sperm extract and 6-DMAP 2 hours after the injection of the donor nucleus, the highest rates of cleavage (79%) and cleavage with normal nuclei (40%) were witnessed.
• Use of sperm extract and 6-DMAP also successfully activated oocytes parthenogenetically, achieving an 83% overall cleavage rate and 73% cleavage rate with normal nuclei.

Conclusions

• Despite the rapid nuclear remodeling observed in equine cytoplasts, the timing of activation did not significantly impact the embryo’s development after reconstruction.
• It was concluded that using a combination of 6-DMAP and sperm extract achieved the best results, highlighting these as the optimal methods for equine nuclear transfer oocyte activation.