Lab-Fertilized Egg Cells Created from Human Skin DNA

Human embryos arise from eggs that utilize the DNA from adult skin cells. This was accomplished with mice. This advancement may offer a pathway for same-sex couples or women facing fertility challenges to have biologically related children.

Researchers have successfully replicated animals through cloning techniques. This involves substituting the nucleus of an egg cell with the nuclei from somatic cells such as skin cells. However, in addition to the legal hurdles surrounding human cloning, many couples desire children that carry genes from both partners, necessitating both sperm and eggs. Shoukhrat Mitalipov of Oregon Health and Science University.

This scenario is complicated by the nature of eggs and sperm being haploid, meaning they contain only one set of chromosomes. The challenge lies in halving the complete set of chromosomes found within cells such as skin cells after selecting an optimal combination of the original genes.

Females develop all of their eggs while still in the womb, where the progenitor cells initially containing 46 chromosomes undergo a complicated process of replication, mixing, and division to reduce to 23 chromosomes.

Mitalipov was intrigued by the possibility of employing natural chemical processes that facilitate chromosomal division in mature human eggs both before and after fertilization to replicate this process in his laboratory.

Having achieved this with mice, Mitalipov and his team are now trialing the method with human subjects. They started by extracting the nuclei from hundreds of eggs donated by healthy women, which were left at a specific development stage linked to chromosomal division. Next, the nuclei of skin cells, known as fibroblasts, from healthy female volunteers were inserted into these eggs. Microscopic images displayed the chromosomes aligned on the spindle and the internal structures necessary for chromosomal separation.

The team then injected sperm from a healthy donor to fertilize some of the eggs, utilizing a method akin to that employed in creating babies using third-party mitochondrial DNA, which can also minimize the risk of specific genetic disorders.

This injection typically causes the eggs to undergo chromosome selection and eliminate duplicate DNA, preparing them for additional reception from the sperm. Nonetheless, in the case of the skin-derived eggs, this process was interrupted, with chromosomes aligning but not separating. Consequently, the researchers attempted again with a new batch of fertilized eggs, applying an electrical pulse that allowed calcium to surge into the egg, emulating natural signals triggered when sperm contact the egg’s outer layer, alongside an incubation period with a drug to activate them from their dormant state pre-fertilization.

Through a series of trials, the researchers successfully halved the chromosome counts in the eggs, discarding any excess. By the conclusion of the experiment, 9% of the fertilized eggs had developed into blastocysts — a dense cluster of cells at about 5-6 days post-fertilization, typically moving into the uterus during IVF treatments. However, the team did not pursue the transfer or sustain the blastocyst beyond six days.

Despite the progress made, the mixtures of genes forming the remaining chromosomes appeared particularly susceptible to defects. “I believe this method is still in its early stages and is not presently suitable for clinical applications,” stated MITINORI SAITOU from Kyoto University in Japan.

Lin from Osaka University noted that while the techniques are “very sophisticated and organized,” they remain “inefficient and potentially hazardous for immediate clinical use.” Nevertheless, Hayashi remarked that the team has achieved a “substantial breakthrough in reducing the human genome.” “This advancement will herald new technologies,” he stated.

Mitalipov acknowledged the validity of the criticisms, emphasizing that his team is actively working to address the existing flaws. “At the end of the day, we’re making progress, but we aren’t there yet,” he remarked.