We were surprised to see how far gastruloids develop, their complex organisation and the presence of early-stage tissues and organ
- Alfonso Martinez Arias
The definitive architecture of the mammalian body is established shortly after the embryo implants into the uterus. This body plan has spatial references, or axes, that guide the emergence of tissues and organs: an antero-posterior axis defined by the head at one end and the tail at the other, an orthogonal dorso-ventral axis and a medio-lateral axis, which orientates the arrangement of internal organs like the liver, pancreas or the heart.
Studying the processes orchestrating the formation of early mammalian embryos is hampered by the difficulty in obtaining them. Earlier findings from the Cambridge group had shown that embryonic stem cells could self-organise in culture into structures with an antero-posterior polarity.
Now, in collaboration with researchers from the University of Geneva and the Swiss Federal Institute of Technology Lausanne (EPFL), they have extended the cultures to reveal a capacity of mouse stem cells to produce ‘pseudo-embryos’ that display some of the important characteristics of a normal mouse embryo. Established from only 300 embryonic stem cells, these structures, called ‘gastruloids’, exhibit developmental features and organisation comparable to the posterior part of a six to ten day-old embryo.
The study shows that gastruloids organise themselves with regard to the three main body axes, as they do in embryos, and follow similar patterns of gene expression. One example of this is the pattern of expression of Hox genes, an ensemble of genes that are expressed in a precise sequential order in the embryo and act as landmarks for different aspects of the body, including the position of different vertebrae or of limbs. This degree of organisation makes gastruloids a remarkable system for the study of the early stages of normal or abnormal embryonic development in mammals.
“These results significantly extend our earlier findings. We were surprised to see how far gastruloids develop, their complex organisation and the presence of early-stage tissues and organ,” says Professor Alfonso Martinez Arias, leader of the University of Cambridge team, at its Department of Genetics.
Image: Seven-day old gastruloid
Credit: Mehmet Girgin, EPFL
Reproduced courtesy of the University of Cambridge