For the first time ever, researchers have been
able to grow a human embryo outside the uterus for 13 days — a
significant improvement over the previous record of nine days and a
development that opens a new window into the hitherto little understood
stages of human ontogenesis. However, the accomplishment puts research
involving in vitro human embryos on a “collision course” with
international regulations that places a 14-day limit on laboratory
studies of embryos.
“This is about much more than just
understanding the biology of implantation embryo development. Knowledge
of these processes could help improve the chances of success of IVF [In
Vitro Fertilization], of which only around one in four attempts are
successful,” Simon Fishel, founder and president of the U.K.’s CARE
Fertility Group, said in a statement.
Fishel is the co-author of one of the two studies published Wednesday, which describe the findings of the research.
One of the key findings of the study was the
surprising discovery that the reorganization of the human embryo that
normally takes place after it has implanted itself into the uterus can
be achieved even in laboratory cultures.
“Embryo development is an extremely complex
process and while our system may not be able to fully reproduce every
aspect of this process, it has allowed us to reveal a remarkable
self-organising capacity of human blastocysts that was previously
unknown,” Marta Shahbazi, a researcher at the University of Cambridge
who co-authored one of the studies, said in a statement.
A blastocyst is a ball of cells that forms
about three days after an egg has been fertilized by a sperm. This clump
of cells then differentiates into tissues that later develop into
organs.
Imaging a human embryo in the absence of maternal tissues - day 10 (left) and day 11 (right). Photo: Zernick-Goetz lab/University of Cambridge
Although the blastocyst stage of human embryos
has been extensively studied and documented, what happens beyond the
seventh day of fertilization — when the embryo must implant itself into
the uterus to survive — still remains shrouded in mystery.
“Implantation is a milestone in human
development as it is from this stage onwards that the embryo really
begins to take shape and the overall body plans are decided. It is also
the stage of pregnancy at which many developmental defects can become
acquired. But until now, it has been impossible to study this in human
embryos,” Magdalena Zernicka-Goetz from the University of Cambridge, who
co-authored both the papers, said in the statement.
In addition to providing invaluable insights
into the earliest stages of human development, the study also rekindles
debate over the internationally-accepted rule, proposed in 1979 and
adopted in the U.K. in 1984, that limits in vitro human embryo research
to up to 14 days after fertilization.
“The 14-day rule was never intended to be a
bright line denoting the onset of moral status in human embryos. Rather,
it is a public-policy tool designed to carve out a space for scientific
inquiry and simultaneously show respect for the diverse views on
human-embryo research,” researchers, not involved in the study wrote, in
a commentary
for the journal Nature. “Some might conclude from such developments
that policymakers redefine boundaries expediently when the limits become
inconvenient for science. If restrictions such as the 14-day rule are
viewed as moral truths, such cynicism would be warranted. But when they
are understood to be tools designed to strike a balance between enabling
research and maintaining public trust, it becomes clear that, as
circumstances and attitudes evolve, limits can be legitimately
recalibrated.”
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