The early stages of development of the human embryo are studied in culture for up to 10-13 days in two separate studies published in Nature and Nature Cell Biology this week. Both studies show that, even in a petri dish, human embryos can self-organize - a process involving cell divisions and shape rearrangements - and that the changes they undergo are similar to those that occur in the presence of maternal cues.
Although very early stages of human embryo development have been studied before, so far it has been challenging to keep human embryos in a petri dish past the seventh day of development, when they usually implant into the womb. Ali Brivanlou and colleagues, writing in a paper published in Nature, and Magdalena Zernicka-Goetz and colleagues, writing in a separate paper in Nature Cell Biology, have shown that the human embryo can self-organize in a petri dish. Using a technique previously developed by the second set of authors for culturing mouse embryos, both groups report various events taking place up to 10-13 days of development, from the formation of the blastocyst - an embryo stage in which cell divisions are underway - to the post-implantation stage, which occurs after the embryo has adhered to the wall of the womb, or, in this case, an attachment substrate. These observations highlight developmental differences between mouse and human embryos, including cell-type specification and tissue organization.
In accordance with internationally recognised guidelines, the experiments were concluded before 14 days into development or the formation of a line of cells known as the primitive streak. In a Comment piece published in Nature this week, Insoo Hyun, Amy Wilkerson and Josephine Johnston explain that the 14-day rule has been effective at permitting research on embryos within strict constraints in part because, until now, it has been technologically challenging for scientists to break it. They stress that this rule was "never intended to be a bright line denoting the onset of moral status in human embryos." Instead, they write, it is "a public-policy tool designed to carve out a space for scientific inquiry and simultaneously show respect for the public's diverse views on research on human embryos." Any decision to revise the rule in light of the evolving science and its potential benefits must depend on how well the proposed changes can achieve these two chief goals, the authors argue. They recommend that any future processes of consensus-building involve experts, policy makers, patients and concerned citizens.
Nature, DOI: 10.1038/nature17948. http://nature.com/articles/doi:10.1038/nature17948. Corresponding Author: Ali Brivanlou
Nature Cell Biology, DOI: 10.1038/ncb3347. http://nature.com/articles/doi:10.1038/ncb3347. Corresponding Author: Magdalena Zernicka-Goetz
Nature Comment, DOI: 10.1038/533169a. Corresponding Author: Insoo Hyun