The challenge faced by developmental biologists is not an easy one: the embryo is a system under continuous change, where single cells navigate space, time, states and fates accordingly to mechanisms that are still poorly understood. Yet, these mechanisms must clearly work in that they consistently allow for the robust and reliable generation of functional adult living systems. How do we reconcile the quickly-changing reality of the developing embryo with the requirements of precise in vitro experimentation?
The short animation above introduces this topic and highlights the mutual relationship between in vivo and in vitro developmental models. By reinterpreting Italian photographer Ugo Mulasâ€™ famous picture series, we here transpose Lucio Fontanaâ€™s spatialist interpretation of art to the developing embryo. Just as Fontana warped the dimensionality of the canvas by slashing it with a razor, developmental biologists interrupt the inexorable progression of developmental time by extracting cells from the inner cell mass. This population we call â€œembryonic stem cellsâ€. From these the AMA lab has developed protocols that allow the generation of self-organising aggregatess: the gastruloids. Developed by learning from the embryo, gastruloids in turn allow to learn about the embryo, and represent in vitro systems where one can investigate in a controllable way the logic whereby cells interpret space and time.
Â an animation by Stefano Vianello
- Music: â€œSoft mischiefâ€ by Jay Man, ourmusicbox.com
- Mouse early development: Sylvain Bessonard, Institut Pasteur, Paris, France
- Picture series: Ugo Mulas â€œLucio Fontanaâ€ (1964)
The left picture is a group of ES cells bearing a reporter for Wnt signalling (red) in adherent culture, the middle one is the same cells in an elongating â€˜organoidâ€ which we call a â€˜gastruloidâ€ -notice the localize expression of the reporter-; finally the picture on the right is an embryo bearing the Wnt reporter at a stage we reckon mimics that of the aggregates in the middle. Picture on the right courtesy of Christoph Budjan.
New publication on â€œsymmetry breaking in ensembles of ES cellsâ€
Progress on our attempts to understand the connection between genes, signals, cells and embryos have just been published in Development. In a first paper we describe a new experimental system in which we coax mouse Embryonic Stem cells to make structures with an anterior posterior axis and a germ layer organization that resembles that of an embryo (http://dev.biologists.org/content/141/22/4231.full). In a second paper we use this experimental system to gain some insights into the emergence of the spinal cord (http://dev.biologists.org/content/141/22/4243.full).
You can see a movie and some thoughts on the experiments here: http://www.cam.ac.uk/research/news/shaping-up-researchers-reconstruct-early-stages-of-embryo-development
More on this will follow soon.
These are three videos from our recent publication in Development (â€œA membrane-associated Î²-catenin/Oct4 complex correlates with ground-state pluripotency in mouse embryonic stem cells.â€ Development. 2013 Mar;140(6):1171-83. doi: 10.1242/dev.085654) which highlight the behaviour of wildtype and ÃŸ-catenin mutant cells in 2i conditions. This study tries to resolve the running controversy about the requirement for ÃŸ-catenin signalling. Our results are in keeping with those of Wray et al. (Inhibition of glycogen synthase kinase-3 alleviates Tcf3 repression of the pluripotency network and increases embryonic stem cell resistance to differentiation. Nat Cell Biol. 2011 Jun 19;13(7):838-45) and extend them to reveal an important interaction between ÃŸ-catenin and Oct4 associated with pluripotency.
For these movies, cells were plated at low density in 2i (N2B27 supplemented with the MEK inhibitor PD03 and the GSK3 inhibitor Chiron). The wild type cells (E14) rapidly stick together to form the aggregates that are characteristic of these culture conditions. You will see this stickiness in the way individual cells get sucked up into the colonies. On the other hand, notice that the ÃŸ-catenin mutant cells have difficulty sticking together and forming the compact structures observed in E14 cells. In ÃŸ-catenin mutant cultures, it is possible to observe constant attempts to differentiate which is consistent with the fragile pluripotency of these cells (remember that they are in 2i!). The third movie shows cells whose only ÃŸ-catenin Â lacks the C terminal domain and therefore cannot mediate transcriptional functions. In fact, the biology of ÃŸ-catenin suggests that this protein is mostly stable at the membrane and this is what we observe. These cells exhibit an intermediate behaviour between the E14s and the ÃŸ-catenin mutants. They adhere to each other though they do not form the tight aggregates that E14 cells do. As these cells are pluripotent this was used by Wray et al to show that the transcriptional function of ÃŸ-catenin is not required for the maintenance of pluripotency (and see also Lyashenko et al. Nat Cell Biol. 2011 Jun 19;13(7):753-61).
Of course there is a lot more in these movies and if you notice something, let us know.