In a study just published in the journal Cell[1]University of Texas researchers say they have evolved “peri-gastruloids,” which they define as “an embryo-like structure” that includes the yolk sac (cf. Human “synthetic embryos”: the announcements multiply).
“The presence of embryonic and extra-embryonic tissue allows researchers to study the interactions between the epiblast, amnion and yolk sac during gastrulation, which has previously been impossible in humans,” said Jun Wu, a biologist at the University of Texas Southwestern Medical Center and lead author of the study. Gastrulation, the stage of embryonic development where the three layers form, occurs between 17 and 21 days after fertilization. However, “for bioethical reasons, human embryos are generally not cultured for more than 14 days” (see Embryo Research: No Limits Anymore?).
Using a different type of stem cell
Instead of using “tethered” pluripotent stem cells[2], researchers more commonly used expanded pluripotent stem cells (EPSC) (see Expanded stem cells, a breakthrough?). It has already been shown that these cells can differentiate into embryonic and extra-embryonic tissue in mice.
By adding the “appropriate growth factors” to human EPSCs, they differentiated into these two tissue types[3]. The cells then “self-organized into structures resembling the human embryo.”
The perigastruloids developed the amniotic sac, in which the embryos live, and the yolk sacs, which provide blood supply to the embryos. In addition, they showed “early signs of organogenesis,” such as neurulation, which marks the beginning of central nervous system development.
No “ethical concerns”?
The researchers consider their method to be “effective and reproducible”. In what they described as a “small-scale experiment,” they produced hundreds of perigastruloids.
“The strength of this model resides in its ability to exploit the remarkable self-assembly ability of human EPSCs with minimal outside intervention,” comments Jun Wu.
The team would like to reassure by claiming that the perigastruloids are not viable “due to the exclusion of the trophoblasts that give rise to the placenta”. “This helps to eliminate the ethical concerns of this research,” say the scientists (cf. Research on the embryo: the ISSCR plays with words).
[1] Jun Wu, Modeling post-implantation stages of human development to early organogenesis with stem cell-derived perigastruloids, Cell (2023). DOI: 10.1016/j.cell.2023.07.018
[2] bonus
[3] Embryonic and extraembryonic
Source: Phys.org, Cell Press (07/20/2023) – Photo: iStock