Scientists have made clusters of human tissue that behave like early embryos, an achievement that promises to transform research into the first preliminary steps of human development.
The clumps of cells, called blastoids, are less than a millimeter wide and look like structures called blastocysts, which are formed within days of an egg being fertilized. Usually blastocysts contain about 100 cells that give rise to every tissue in the body.
Two research teams found that they can make small blastoids from stem cells or reprogrammed skin cells by culturing them in 3D wells filled with a sauce that contains the chemicals needed for normal blastocyst formation.
In separate articles published in Nature, the scientists describe how the cells were composed into ball-shaped blastoids themselves after six to eight days in culture. Tests have shown that it contains all the cells seen in natural blastocysts. Some attached to plastic culture dishes, which mimicked the process of implantation in the uterus.
By studying blastoids, scientists hope to learn how newly formed embryos develop in the run-up to implantation, and to understand why so many miscarriages occur at this delicate stage of human pregnancy.
Further work will use the cells to understand how specific birth defects can arise and to investigate the impact of environmental toxins, drugs and even viral infections on a healthy embryonic development.
“The ability to work on a scale, we think, will revolutionize our understanding of these early stages of human development,” Prof José Polo, who led one of the teams, told Monash University in Australia.
Until now, research on the earliest stages of human development has relied heavily on couples donating surplus IVF embryos to science. The practice attracted ethical objections, and limited donations limited scientific progress. By law, researchers can only study human embryos until they are 14 days old.
The creation of blastoids must overcome these problems by allowing scientists to make hundreds of embryo-like structures in the laboratory.
“We are very excited,” said Jun Wu, an assistant professor at the University of Texas at Dallas, Texas and leader of a separate team. ‘Studying human development is really difficult, especially at this stage of development. It’s essentially a black box. Wu said the blastoids were cultured to the equivalent of about day 10 for a human embryo.
Naomi Moris, of the Francis Crick Institute in London, who uses stem cells to model human embryo development, calls the work important and emphasizes the rapid progress being made in the field. “The excitement of these models is that we can hopefully use them to gain an understanding of how normal human development proceeds and what processes can play out when things go wrong, for example in miscarriage or congenital disorders,” she said.
Polo and Wu said that although blastoids were similar to embryos in the early stages, they were not identical and could only mimic the first week of human development. The approach will not be used to make embryos for implantation, said Amander Clark, of the University of California, Los Angeles, who worked with Polo.
But in an accompanying article in Nature, scientists at the University of Michigan suggested that advances in science would lead to blastoids that closely mimicked human blastocysts.
The scientists, Yi Zheng and Jianping Fu, wrote: “This will inevitably lead to bioethical questions. What should be the ethical status of human blastoids, and how should they be regulated? Should the 14-day rule apply? These questions must be answered before research on human blastoids can proceed with the necessary caution. ”