In a first, scientists create embryos in a lab from stem cells of monkey

This is why very less information is available on human embryos and early organ development. The Chinese researchers claim that their study could change this.

“Because monkeys are closely related to humans evolutionarily, we hope the study of these models will deepen our understanding of human embryonic development, including shedding light on some of the causes of early miscarriages,” said Zhen Liu, one of the study authors, in a press release.

Developing embryos out of monkey stem cells

The Chinese researchers began their experiment with the embryonic stem cells of a macaque. They cultured the cells in vitro and added various growth factors in the culture that also included additional non-human primate stem cells. This led to the formation of blastoids, embryonic structures similar to the blastocyst stage of natural embryos. 

The blastoids gave rise to the yolk sac and further turned into real embryo-like cells that generally led to the development of the three embryonic germ layers. In mammals, these layers (ectoderms, mesoderm, and endoderm) form all the body parts in a fetus ranging from skin to heart and nervous system.

The researchers employed RNA sequencing to compare gene expression in the cultured embryo structures with that observed in natural blastocysts. They noticed striking similarities between the two and this encouraged them to further test the cultured embryo in eight female monkeys.

They were able to successfully implant the embryonic structures (at the blastoid stage) into the uteruses of three female monkeys. “Monkey blastoids were very likely to develop gastrulation with major germ-layer formation and lead to early pregnancy under in vitro prolonged culture,” the researchers note.

The goal of this experiment was to check if their lab-grown embryos could trigger the same hormonal activities as found during normal pregnancy. Although the implanted blastoids did activate the release of pregnancy hormones such as chorionic gonadotropin (hCG) and progesterone, none of them developed into fetuses. 

They further added, “The suspected gestation sacs and yolk sac disappeared without any further development.” The study authors are now trying to create a better embryo-culturing system to produce monkey embryos out of stem cells. 

Further application of monkey blastoids can help to dissect the molecular mechanisms of primate embryonic development,” said Fan Zhou, one of the corresponding authors.

The CAS team believes that since their in-vitro embryos don’t have the ability to develop into living organisms, they are different from natural embryos and therefore, can be considered for studying early embryonic development in detail. 

The study is published in the journal Cell Stem Cell.

Study Abstract:

Human stem cell-derived blastoids display similar morphology and cell lineages to normal blastocysts. However, the ability to investigate their developmental potential is limited. Here, we construct cynomolgus monkey blastoids resembling blastocysts in morphology and transcriptomics using naive ESCs. These blastoids develop to embryonic disk with the structures of yolk sac, chorionic cavity, amnion cavity, primitive streak, and connecting stalk along the rostral-caudal axis through prolonged in vitro culture (IVC). Primordial germ cells, gastrulating cells, visceral endoderm/yolk sac endoderm, three germ layers, and hemato-endothelial progenitors in IVC cynomolgus monkey blastoids were observed by single-cell transcriptomics or immunostaining. Moreover, transferring cynomolgus monkey blastoids to surrogates achieves pregnancies, as indicated by pro- gesterone levels and presence of early gestation sacs. Our results reveal the capacity of in vitro gastrulation and in vivo early pregnancy of cynomolgus monkey blastoids, providing a useful system to dissect primate embryonic development without the same ethical concerns and access challenges in human embryo study.