Japanese scientists say they have created healthy baby mice from eggs they made entirely in the lab using a sample of mouse skin cells.
The pups born from the eggs appeared to be healthy and were able to go on to have babies themselves.
Experts say the findings, in Nature journal, offer future hope of artificial eggs for couples who need fertility treatment.
But they say many more years of study is needed to make that leap to humans.
Scientists have already been able to make sperm in the lab, but for that feat they used an immature embryonic stem cell, which is known to be able to morph into any type of cell.
Taking a grown-up skin cell and getting it to change into an egg is more challenging, say experts.
The Japanese team, Prof Katsuhiko Hayashi and colleagues, took cells from a mouse tail and reprogrammed these adult cells back into immature ones.
Then, they coaxed these immature stem cells to become an egg.
Not all of the eggs that they made in the lab were healthy or viable.
But the ones that were could be fertilised by sperm in a dish.
When these fertilised eggs were put into the wombs of adult female mice, they developed into apparently healthy babies.
Experts warn there are many barriers to using the same method in humans.
Some are technical, but arguably the biggest ones are about safety and ethics.
Flaws in artificial eggs might be passed on to future generations, for example.
The technique the Japanese researchers used still required harvesting some tissue from embryos to support the artificial eggs as they matured in lab dishes.
Prof Richard Anderson, from the MRC Centre for Reproductive Health at the University of Edinburgh, said: “One day this approach might be useful for women who have lost their fertility at an early age, as well as for improvements in more conventional infertility treatments.
“But the very careful analyses in this paper show the complexity of the process and how it is a long way from being optimised.”
Prof Azim Surani has been studying how to turn human skin cells into the precursors of sperm and eggs in his lab.
He said: “As far as humans are concerned, we are way behind.
“We can’t be sure the same will apply with human cells.”
He said it was futile to speculate when that breakthrough might come, but it was worth preparing for.
“Ethically, this issue has yet to be discussed fully by the scientists and society,” Prof Surani said.
“These discussions have occurred in the past, and are continuing within the regulatory bodies, certainly in the UK.
“This indeed is the right time to start a debate and involve the wider public in these discussions, long before and in case the procedure becomes feasible in humans.”
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Healthy mice from lab-grown eggs