Developmental biologists have grown human embryos in the lab for up to 13 days after fertilization, shattering the previous record of 9 days.
But the widely hailed results also set science on a collision course with national laws and ethical guidelines, experts cautioned.
Most of the countries enforce the “14-day rule”, which says that human embryos cannot be cultured in the lab for more than two weeks. The authors of the studies ended their experiments before this point.
This rule has never been seriously challenged simply because no one had succeeded in keeping the embryos alive that long.
The achievement has already enabled scientists to discover new aspects of early human development, including features never before seen in a human embryo.
The technique could help to determine why some pregnancies fail.
The Research Work on Human Embryos:
The work, reported this week in Nature and Nature Cell Biology, also raises the possibility that scientists could soon culture embryos to an even more advanced stage.
Scientists have well understood the earliest stages of life in many other animals for decades.
“It’s really embarrassing at the beginning of the twenty-first century that we know more about fish and mice and frogs than we know about ourselves,” says Ali Brivanlou, a developmental biologist at the Rockefeller University in New York City and lead author of the study in Nature. “This is a bit difficult to explain to my students.”
Next to nothing is known about how the small, hollow bundle of cells called a blastocyst — emerging from a fertilized 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 Brivanlou.
“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 fetus and its placenta.
But unlike earlier experiments, in which growth has rarely continued beyond seven days, the embryos showed an unexpected ability to self-organize.
“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.
It had long been assumed that this transformation could not persist detached from the mother’s uterus.
In the near future, the ability to study implantation in culture is likely to shed light on why some early miscarriages occur and why in vitro fertilisation has a high failure rate.