A new technique that allows embryos to develop in vitro beyond the implantation stage (when the embryo would normally implant into the womb) has been developed by scientists at the University of Cambridge allowing them to analyse for the first time key stages of human embryo development up to 13 days after fertilisation. The technique could open up new avenues of research aimed at helping improve the chances of success of IVF.
Once an egg has been fertilised by a sperm, it divides several times to generate a small, free-floating ball of stem cells.
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Bioethicists from Case Western Reserve University School of Medicine and The Hastings Center, working with a research administrator at The Rockefeller University, are proposing a reexamination of an internationally recognized rule limiting in vitro research on human embryos to 14 days post-fertilization. Under the rule, such research is permitted before the cut-off date at 14 days and prohibited thereafter.
Ref: Self-organization of the human embryo in the absence of maternal tissues. Nature Cell Biology (4 May 2016) | DOI: 10.1038/ncb3347
ABSTRACT
Remodelling of the human embryo at implantation is indispensable for successful pregnancy. Yet it has remained mysterious because of the experimental hurdles that beset the study of this developmental phase. Here, we establish an in vitro system to culture human embryos through implantation stages in the absence of maternal tissues and reveal the key events of early human morphogenesis. These include segregation of the pluripotent embryonic and extra-embryonic lineages, and morphogenetic rearrangements leading to generation of a bilaminar disc, formation of a pro-amniotic cavity within the embryonic lineage, appearance of the prospective yolk sac, and trophoblast differentiation. Using human embryos and human pluripotent stem cells, we show that the reorganization of the embryonic lineage is mediated by cellular polarization leading to cavity formation. Together, our results indicate that the critical remodelling events at this stage of human development are embryo-autonomous, highlighting the remarkable and unanticipated self-organizing properties of human embryos.
Ref: Self-organization of the in vitro attached human embryo. Nature (4 May 2016) DOI: 10.1038/nature17948
ABSTRACT
Implantation of the blastocyst is a developmental milestone in mammalian embryonic development. At this time, a coordinated program of lineage diversification, cell-fate specification, and morphogenetic movements establishes the generation of extra-embryonic tissues and the embryo proper, and determines the conditions for successful pregnancy and gastrulation. Despite its basic and clinical importance, this process remains mysterious in humans. Here we report the use of a novel in vitro system to study the post-implantation development of the human embryo. We unveil the self-organizing abilities and autonomy of in vitro attached human embryos. We find human-specific molecular signatures of early cell lineage, timing, and architecture. Embryos display key landmarks of normal development, including epiblast expansion, lineage segregation, bi-laminar disc formation, amniotic and yolk sac cavitation, and trophoblast diversification. Our findings highlight the species-specificity of these developmental events and provide a new understanding of early human embryonic development beyond the blastocyst stage. In addition, our study establishes a new model system relevant to early human pregnancy loss. Finally, our work will also assist in the rational design of differentiation protocols of human embryonic stem cells to specific cell types for disease modelling and cell replacement therapy.