Scientists reported today they had grown human embryos in the lab for nearly two weeks, an unprecedented feat that promises advances in assisted reproduction, stem-cell therapies and the basic understanding of how human beings form.
Besides opening a window onto the first steps in the creation of an individual, the findings in parallel studies may help explain early miscarriages and why in vitro fertilisation has such a high failure rate.
The research also showed for the first time that newly-forming human embryos can mature beyond a few days outside a mother's womb, something that was previously thought to be impossible.
But the widely hailed results also set science on a collision course with national laws and ethical guidelines, experts cautioned.
Up to now, a so-called "14-day rule" -- which says that human embryos cannot be cultured in the lab for more than two weeks -- has never been seriously challenged simply because no one had succeeded in keeping them alive that long.
In this case, the scientists destroyed the embryos to avoid breaching that limit. The findings were published in Nature and Nature Cell Biology.
Next to nothing is known about how the small, hollow bundle of cells called a blastocyst -- emerging from a fertilised egg -- attach to the uterus, allowing an embryo to begin to take shape.
"This portion of human development" -- called implantation -- "was a complete black box," said Ali Brivanlou, a professor at The Rockefeller University in New York, and the main architect of the Nature study.
Building on previous work with mice, Brivanlou and colleagues concocted a chemical soup and scaffolding to duplicate this process "in vitro", or in a petri dish.
"We were able to create a system that properly recapitulates what happens during human implantation," said Rockefeller scientist and lead author Alessia Deglincerti.
As hoped, the blastocyst grew, beginning to divide into the different types of cells that eventually give rise to a foetus and its placenta.
But unlike earlier experiments, in which growth has rarely continued beyond seven days, the embryos showed an unexpected ability to self-organise.
"Amazingly, at least up to the first 12 days, development occurred normally in our system in the complete absence of maternal input," Brivanlou said in a statement.
