Scientists Create Three-Parent Embryos

On February 5, 2008, Reuters reported the groundbreaking achievements of a group of reproductive researchers from New Castle University, England who created a three-parent embryo. The idea behind the creation of the human embryo is to prevent the inheritance of defective mitochondria from mother to child, protecting the child from the fatal genetic diseases.

Dr. John Zhang is a pioneer in the field of nuclear transfer. He successfully studied the progress of a fetus up to 29 weeks after nuclear transfer. He presented this highly acclaimed innovative research in 2003 at the annual meeting of American Society for Reproductive Medicine (ASRM). Dr. Zhang's original work was published in the journal Fertility and Sterility (80: Supplement 3, S56, 2003) as an article entitled "Pregnancy Derived from Human Nuclear Transfer," in which he was the primary author.

What is Nuclear Transfer?

In higher organisms including humans, both nucleus and mitochondria (an organelle responsible for energy synthesis located outside the nucleus in the cytoplasm) contain DNA. In normal sexual reproduction, offspring inherit their mitochondrial DNA from the mother. This type of inheritance pattern is generally known as maternal inheritance. But, when the mother passes defective mitochondria to the child, fatal heart, liver, brain or muscular disorders can result.

The only possible method to overcome this situation is through nuclear transfer, which allows the mother to provide her nuclear DNA to the child, but not her (defective) mitochondrial DNA. Nuclear transfer is an invasive procedure where an in-vitro fertilized egg's nucleus (from two parents) is transferred into an enucleated ovum (egg cell with the nucleus removed) provided by a third donor. The purpose of the donation of an enucleated cell is to provide the child with non-defective mitochondria, from a woman other than the mother. This results in a three-parent embryo. Its nucleus is formed by the fusion of sperm and mother's oocyte nucleus, and its cytoplasm is provided by the enucleated donor cell. This results in the inheritance of DNA from three different sources, the nuclear DNA is from sperm and recipient oocyte, and the mitochondrial DNA is mainly through the donor. See the Reuters link.