Cambridge scientists have created a stem cell-derived model of the human embryo in the lab by reprogramming human stem cells. The breakthrough could help research into genetic disorders and in understanding why and how pregnancies fail.
Published today in the journal Nature, this embryo model is an organised three-dimensional structure derived from pluripotent stem cells that replicate some developmental processes that occur in early human embryos.
Use of such models allows experimental modelling of embryonic development during the second week of pregnancy. They can help researchers gain basic knowledge of the developmental origins of organs and specialised cells such as sperm and eggs, and facilitate understanding of early pregnancy loss.
In natural human development, the second week of development is an important time when the embryo implants into the uterus. This is the time when many pregnancies are lost.
The new advance enables scientists to peer into the mysterious ‘black box’ period of human development — usually following implantation of the embryo in the uterus — to observe processes never directly observed before.
Understanding these early developmental processes holds the potential to reveal some of the causes of human birth defects and diseases, and to develop tests for these in pregnant women.
Until now, the processes could only be observed in animal models, using cells from zebrafish and mice, for example.
Legal restrictions in the UK currently prevent the culture of natural human embryos in the lab beyond day 14 of development: this time limit was set to correspond to the stage where the embryo can no longer form a twin.
Zernicka-Goetz says the while these models can mimic aspects of the development of human embryos, they cannot and will not develop to the equivalent of postnatal stage humans.
Over the past decade, Zernicka-Goetz’s group in Cambridge has been studying the earliest stages of pregnancy, in order to understand why some pregnancies fail and some succeed.
In 2021 and then in 2022 her team announced in Developmental Cell, Nature and Cell Stem Cell journals that they had finally created model embryos from mouse stem cells that can develop to form a brain-like structure, a beating heart, and the foundations of all other organs of the body.
The new models derived from human stem cells do not have a brain or beating heart, but they include cells that would typically go on to form the embryo, placenta and yolk sac, and develop to form the precursors of germ cells (that will form sperm and eggs).
Many pregnancies fail at the point when these three types of cells orchestrate implantation into the uterus begin to send mechanical and chemical signals to each other, which tell the embryo how to develop properly.
There are clear regulations governing stem cell-based models of human embryos and all researchers doing embryo modelling work must first be approved by ethics committees. Journals require proof of this ethics review before they accept scientific papers for publication. Zernicka-Goetz’s laboratory holds these approvals.
Bailey A. T. Weatherbee, Carlos W. Gantner, Lisa K. Iwamoto-Stohl, Riza M. Daza, Nobuhiko Hamazaki, Jay Shendure, Magdalena Zernicka-Goetz. A model of the post-implantation human embryo derived from pluripotent stem cells. Nature, 2023; DOI: 10.1038/s41586-023-06368-y
University of Cambridge. (2023, June 27). Human embryo-like models created from stem cells to understand earliest stages of human development. ScienceDaily. Retrieved June 27, 2023 from www.sciencedaily.com/releases/2023/06/230627123010.htm
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