Embryologist loading oocytes with syringe into cell-culture dish. (Photo by Svitlana Hulko on Shutterstock)

In A Nutshell

Scientists put a skin-cell nucleus into a donated egg and added sperm; an extra activation step was needed to start division.

Embryos formed, but chromosome sorting was random and lacked recombination, unlike natural egg formation.

Only a small fraction reached the blastocyst stage; standard IVF controls did much better.

This is a lab demonstration, not a treatment. Major biological hurdles remain before any clinical use.

PORTLAND, Ore. — Researchers have created human embryos by taking nuclei from ordinary skin cells, placing them into donated eggs, and fertilizing them with sperm. The work is a laboratory demonstration that shows what might eventually be possible for people who cannot produce viable eggs, though substantial scientific hurdles remain.

The team at Oregon Health & Science University used a technique called somatic cell nuclear transfer, where a skin cell’s nucleus is placed into a donated egg that has had its own genetic material removed. After fertilization with sperm, these reconstructed cells produced embryos that developed for several days. While purely experimental and years from clinical use, the research published in Nature Communications shows an early demonstration of mitomeiosis, the team’s term for inducing a meiosis-like division in a somatic genome, which could one day help women without functional eggs have genetically related children.

“Infertility affects millions of individuals worldwide and is often caused by the absence of functional gametes,” the researchers wrote. For women, age-related decline in egg quality becomes a primary factor after the mid-thirties, and current fertility treatments cannot help those who lack viable eggs altogether.

How Skin Cells Became Egg-Like Structures

The process takes a skin cell’s nucleus and inserts it into a donated egg cell that has had its own genetic material removed, a technique called somatic cell nuclear transfer or SCNT. Scientists have used this method for decades to clone animals, but the Oregon team adapted it for a different purpose: creating reconstructed cells that could potentially be fertilized like natural eggs.

When a skin cell nucleus enters the donor egg environment, something unexpected occurs. The egg cytoplasm, which provides the cellular machinery needed for division, forces the skin cell’s chromosomes to organize themselves into a spindle structure similar to what occurs in natural eggs. Within about two hours after the transfer, visible spindles formed in about 77% of the reconstructed cells.

This happens even though skin cells have not undergone the DNA replication that normally precedes cell division. Natural eggs contain duplicated chromosomes, each consisting of two connected copies called sister chromatids. The skin cell chromosomes, by contrast, are single, non-duplicated copies. Yet the donor egg cytoplasm coaxes them into forming a division-ready structure anyway.

Researchers at OHSU have demonstrated a new technique to treat infertility by turning skin cells into oocytes, or eggs. Shown here, an image of an oocyte with a bright image of a skin cell nucleus before fertilization. (Credit: Oregon Health & Science University) Overcoming A Major Fertility Obstacle

When researchers added sperm to these reconstructed cells, most got stuck. Natural eggs know how to respond when sperm enters: they complete their division and prepare genetic material from both parents to combine. But about three-quarters of the reconstructed cells just froze in place.

Applying artificial activation using electrical pulses and a chemical called roscovitine solved this problem. This supplemental treatment successfully triggered the division process, causing the cells to split their chromosomes between a pronucleus and a discarded polar body, similar to how natural eggs behave after fertilization. With this approach, about 78% of the cells extruded a polar body and about 76% formed two pronuclei: one from the skin cell chromosomes and one from sperm.

Chromosomes Sorted Randomly, Not in Organized Pairs

To track what happened to individual chromosomes during this unusual process, researchers recruited a family with parents from different ethnic backgrounds. They used skin cells from the daughter and sperm from an unrelated donor. By reading the DNA sequences, they could tell which chromosomes came from the daughter’s mother, which from her father, and which from the sperm donor.

The team looked at 90 embryos. In about 54% of cases, the chromosomes split between two compartments. But the way they split looked nothing like what happens in natural eggs.

When eggs form naturally, matching chromosomes from your mother and father pair up, line up together, and separate in an organized way. One goes to the egg, one gets discarded. It’s precise and orderly. In these reconstructed cells, chromosomes just scattered randomly. Some cells kept both copies of certain chromosomes while completely losing others.

In the remaining 46% of embryos, no splitting happened at all. Most kept all 46 chromosomes instead of reducing to 23 like natural eggs do.

Among the embryos that did split their chromosomes, the numbers varied wildly. Some ended up with as few as 3 chromosomes, others with as many as 43. Most fell somewhere in the middle around 23, but which specific chromosomes stayed and which left was essentially a coin flip for each pair.

One chromosome behaved oddly. Chromosome 8 consistently sent the mother’s copy to one location and the father’s copy to another, rather than choosing randomly. Why this happened remains a mystery.

Most Embryos Stopped Developing Early

When researchers fertilized the reconstructed cells and applied activation treatment, most cleaved into multiple cells. However, only 8.8% developed into blastocysts, the stage at which embryos are typically transferred during IVF treatments. By comparison, 59% of normally fertilized control eggs reached this stage.

Single-cell analysis revealed varied chromosome compositions. Some embryos were uniform, with all cells containing the same mix of sperm and skin cell chromosomes. Others were mosaic, with different cells carrying different chromosome combinations. Nearly all embryos contained the complete set of 23 sperm chromosomes, though one mosaic embryo was missing some sperm chromosomes. The number and origin of skin cell chromosomes varied considerably, creating chromosomal imbalances that likely explain why most embryos stopped developing.

Researchers cultured no embryos beyond day six, adhering to ethical guidelines for research with human embryos.

Years of Work Ahead Before Clinical Use

The scientists stress this is just an early laboratory experiment, not a treatment. Several major biological problems need solving before this could ever help anyone.

First, the random chromosome sorting is nothing like natural egg formation, where chromosomes pair up and separate in an organized way. Second, natural eggs shuffle genetic material between chromosome pairs through a process called recombination, creating genetic diversity. That didn’t happen here at all. Third, the resulting chromosome imbalances would almost certainly prevent a successful pregnancy.

Lead researcher Shoukhrat Mitalipov noted the team cannot yet tell whether embryos failed because of wrong chromosome numbers or because the skin cell DNA wasn’t properly reprogrammed to act like egg DNA. Probably both factors contributed.

Similar experiments in mice have produced live offspring, but mouse and human reproduction work differently enough that success in mice doesn’t guarantee the approach will translate.

If scientists can eventually solve these problems, this type of technique might help women born without ovaries or whose eggs have been damaged by cancer treatment, medical conditions, or age. Right now, these patients can only use donor eggs or pursue adoption.

One striking fact: natural egg development takes more than a decade in humans, starting before birth and finishing only after puberty. A laboratory approach might potentially compress that timeline to weeks, though major scientific questions remain unanswered.

The research received funding from Open Philanthropy, Haploid Gamete Research Foundation, Longevity Impetus, and Oregon Health & Science University. Egg donors received between $7,000 and $8,000, standard compensation for egg donation in Portland, Oregon, and approved by ethics reviewers.

Paper Summary Methodology

Researchers obtained mature eggs from healthy donors aged 21-35 following standard ovarian stimulation protocols. They removed the spindle-chromosome complex from 270 eggs and fused the remaining egg cytoplasm with skin cells that had been synchronized to a non-dividing state. After allowing two hours for spindle formation, they either fertilized these reconstructed cells with sperm using intracytoplasmic sperm injection or activated them artificially.

Because fertilization alone proved insufficient, the team developed a supplemental activation protocol using electrical pulses to trigger calcium release, followed by four-hour treatment with roscovitine, a chemical that inhibits proteins keeping cells in metaphase arrest. They then cultured resulting embryos for up to six days while monitoring development with time-lapse imaging.

To track chromosome inheritance, researchers designed a custom genetic sequencing panel targeting 630 specific genomic locations that could distinguish between maternal and paternal skin cell chromosomes and sperm chromosomes. They collected and individually sequenced polar bodies, pronuclei, and individual cells from embryos.

Results

Approximately 77% of reconstructed cells formed visible spindles within two hours of skin cell fusion. When fertilized with sperm alone, only 23% successfully completed division, but supplemental activation with electrical pulses and roscovitine increased the polar body extrusion rate to about 78% and pronuclei formation to about 76%. About 83% underwent cleavage, though only 8.8% reached the blastocyst stage compared to 59% for normally fertilized control eggs.

Chromosome analysis of 90 embryos showed that 45.6% experienced no segregation (39 retained all 46 skin cell chromosomes in the pronucleus, 2 extruded all into the polar body). Among the 54.4% that divided, chromosomes segregated to produce an average of 23 in the pronucleus and 23 in the polar body, but distribution was random rather than following the organized homolog pairing seen in natural meiosis. No genetic recombination between homologous chromosomes occurred. One exception to random segregation was observed: chromosome 8 showed preferential segregation of maternal homologs to pronuclei and paternal homologs to polar bodies.

In fertilized embryos, all 23 sperm chromosomes were typically present (with one mosaic embryo exception where not all sperm chromosomes were detected), but skin cell chromosome numbers varied from 6 to 46, creating chromosomal imbalances. Some embryos were uniform with consistent chromosome composition across all cells, while others were mosaic with different cells containing different chromosome sets.

Limitations

Random chromosome segregation without proper homolog pairing differs fundamentally from natural meiosis and results in chromosomal imbalances incompatible with normal development. The absence of crossover recombination eliminates a key source of genetic diversity. The low blastocyst development rate (8.8%) likely reflects both chromosomal abnormalities and incomplete epigenetic reprogramming of skin cell DNA.

Researchers note they cannot currently distinguish developmental arrest caused by chromosome imbalances from that caused by reprogramming failures. The metaphase cytoplasm of mature eggs lacks many molecular components required for natural meiosis, including proteins that enable homolog recognition and pairing. The structural state of skin cell chromosomes may prevent proper recognition mechanisms from functioning.

Funding and Disclosures

Open Philanthropy, Haploid Gamete Research Foundation, Longevity Impetus, and Oregon Health & Science University institutional funds provided grants for the research. The authors declared no competing interests. The OHSU Institutional Review Board approved the study with oversight from a Data Safety Monitoring Committee.

Publication Information

Marti Gutierrez, N., Mikhalchenko, A., Shishimorova, M., et al. “Induction of experimental cell division to generate cells with reduced chromosome ploidy.” Nature Communications 16, 8340 (2025). https://doi.org/10.1038/s41467-025-63454-7. Published online September 30, 2025.