A team of developmental scientists from the University of Cambridge and Rockefeller University have grown a human embryo in a lab for a record of 13 days after fertilization


The growth of human embryos outside the womb (in vitro) has always been a hot topic of ethical debate.  At least 12 countries including the United Kingdom prevent scientists from working with embryos older than 14 days. In the United States these guidelines date back to 1979 on the basis that 14 days marked the beginning of gastrulation (a time where a spherically shaped embryo further divides into a multilayered organism) in humans, and is incidentally the latest point that the embryo can split into identical twins. After this time, the embryo becomes a unique individual.

Magdalena Zernicka-Goetz, a developmental biologist at the University of Cambridge, UK and her colleagues developed a method of growing mouse embryos in vitro. A gel matrix enriched with oxygen instead of the usual layer of maternal cells was used to grow mouse embryos. The mouse embryos survived past the gastrulation stage.

The mouse model was then adapted to their research on human embryos which were donated by in vitro fertilization clinics. Zernicka-Goetz et al were able to grow human embryos in a lab for up to 13 days after fertilization beating the previous record of 9 days. In keeping with the 14 day embryology policy the study ended on Day 14.

As the embryonic cells began to differentiate they started to reveal features unique to human development. For example, a group of cells that show up in the embryo at day 10 disappears by day 12. The cell cluster seems to be a transient organ, one that appears and disappears before birth.

In vitro studies could be instrumental in exploring the reasons behind birth defects or the effects of toxic compounds. The fertility industry could also benefit since the survival rate for embryos implanted in a mother’s uterus is 50% and in vitro studies could shed some light onto some of the reasons why.

Whether the embryos would have survived past the 14 day mark is up for conjecture. However, the authors state that this is unlikely since their mouse model suggests that human embryos need a mix of hormones and maternal nutrients for survival. The embryos may also require a 3D scaffold to grow on instead of a 2D plane.

Lastly, these current findings may re-open the heated debate of when an embryo can be considered a person, leading to a re-visiting of the 14 day rule.




Written by: Aurelie Hartawidjojo, BSc, BScPT

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