Scientists used a similar process to the one used to clone the famous Dolly the Heap to create human eggs in the lab and turned them into embryos using in vitro fertilization (IVF).
Although this method is far from being used in a clinical setting, it hopes it could ultimately pave the way for new fertility treatments.
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The proof-of-concept experiment is explained on Tuesday (September 30th) in Nature Communications magazine.
The egg-making process involved removing the nucleus from existing human egg cells and replacing it with human skin cells for the nucleus. This first step, called somatic cell nuclear transfer, is used to clone a variety of animals, including Dolly.
However, OHSU researchers aim to create functional eggs rather than clones, which carry half the chromosome as non-germ cells in the body. During fertilization, 23 chromosomes in the egg are combined with 23 chromosomes from the sperm cells, resulting in a total of 46. The makeshift eggs urged to run half of the chromosome, and scientists applied an electric pulse and a drug called roscovitine.
According to the statement, the experiment ultimately fertilized 82 egg cells in sperm by in vitro fertilization (IVF). However, the fertilization step is not yet completely difficult. Only about 9% have reached the “blastocyst” stage. At that point, the eggs divided and formed hollow spheres of cells that could be introduced into the uterus via IVF.
Most of the eggs fertilized in this study did not reach the blastocyst stage, and in fact only divided enough times to produce a total of 4-8 cells.
The developmental rate of “conservative” blastocysts is likely due to two factors, the study authors wrote in their paper. First of all, chromosomal abnormalities may have stopped the fertilized egg from dividing further. Second, genes exchanged from skin cells are likely not successfully reprogrammed to maintain embryonic development. In other words, in some respects, genes were activated as if they were in skin cells, rather than in cells that formed early in development.
It is unclear which questions presented the larger issues in this study, but it is likely that both factors contributed, the authors wrote.
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None of the eggs reached the blastocyst stage have increased any further, and the chromosomal abnormalities are so stiff that they are unlikely to have been suitable for use in IVF, the researchers noted. These abnormalities included too many or too few chromosomes, but on average it reached 46. Some eggs either carried multiple copies of the same chromosome or were completely missing certain chromosomes.
So for now, the method is “inefficient, risky and cannot be applied immediately to clinical applications,” researchers from Hayashi, a stem cell researcher at Osaka University who was not involved in the study, told Science News.
The study author also stated, “It remains a proof of concept at this stage and further research is needed to ensure efficacy and safety before future clinical applications.”
Looking forward to it, the team plans to study how to better regulate half of the chromosomes in eggs. The goal is to better grasp what happens in natural human pregnancy, and to lose the right chromosome in the first half and pair properly with the new chromosome during fertilization.
If one day the technique can be refined to be used in fertile treatment, it raises ethical questions, experts told NPR. For example, Ronald Green, a bioethicist at Dartmouth College, told NPR that people could ensure that they would collect skin cells from others, including celebrities, without knowledge. “It’s theoretical possibility, but it’s not crazy,” he said.
Other labs are working on a variety of approaches to making eggs in the lab. Stem cells were used to grow stem cells, starting with stem cells or adult cells, then returning to stem cells. This approach has shown some success in mouse experiments, but progress has slowed down in human terms.
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