Production of a mitochondrial-DNA identical cloned foal using oocytes recovered from immature follicles of selected mares.

This research article outlines the successful process and outcomes of producing a cloned horse, also know as a foal, with identical mitochondrial DNA to the original donor, using oocytes recovered from a small selection of related mares.

Background

• The research was undertaking based on the discovery that cloned animals typically possess mitochondria that differs genetically from the donor animal, creating concern within the horse breeding community as maternal lines are held in high regard, so too is athletic performance, thus the genetic value of the offspring is paramount.

Method

• To clone a foal with identical mitochondrial DNA, the researchers harvested oocytes from the immature follicles of two mares, who were maternally related to the donor stallion.
• These oocytes were matured in vitro, and following enucleation, the oocytes were combined with donor cells that had been treated with roscovitine.
• The resulting blastocysts were then transcervically transferred to recipient mares.

Results

• From the first mare, 45 oocytes were collected across ten sessions. Twelve of these oocytes matured and seven were recombined successfully. Despite producing one blastocyst, no pregnancy resulted from this process.
• From the second mare 53 oocytes were harvested from just three sessions. These yielded 27 successfully recombined oocytes which were then treated with either Scriptaid or a combination of Scriptaid and Vitamin C for the first 12 to 16 hours of embryo culture.
• Both treatments resulted in the production of two blastocysts each, and one successful pregnancy after a transfer from the Scriptaid treatment specifically.
• The foal that resulted from this pregnancy subsequently showed that both its genomic DNA and mitochondrial DNA matched the original donor animal, demonstrating the viability of this process.

Conclusion

• The researchers concluded that cloning foals with mitochondrial-identical DNA is achievable using a selective process of oocyte recovery from a limited selection of mares.
• Interestingly, there were significant differences between the two mares used in the study, with one yielding significantly fewer oocytes and successful recombinations per oocyte recovered.