Scientists at the University of California, Santa Cruz (UCSC), used CRISPR to engineer cellular models of embryos that mimic what happens in the first few days after reproductive cells meet. These embryoids are self-organized, three-dimensional cultures that mimic aspects of early embryonic development. Scientists can use these models to study how specific genes influence early development as well as to better understand developmental disorders and improve human fertility.
Full details of the work are published in a newCell Stem Cell paper titled, “Self-organization of embryonic stem cells into reproducible pre-gastrulation embryo models via CRISPRa programming.”
According to Ali Shariati, PhD, an assistant professor of biomolecular engineering at UCSC and the study’s senior author, his team was “interested in recreating and repurposing natural phenomena, such as formation of an embryo, in the dish to enable studies that are otherwise challenging to do with natural systems.”
In animals where the entire process of cell division and organization into a multicellular embryo occurs in utero, it is difficult for scientists to study emerging problems and assess the effect of specific risk factors. “We want to know how cells organize themselves into an embryo-like model, and what could go wrong when there are pathological conditions that prevent an animal from successfully developing,” Shariati said.
For this study, the team used mouse stem cells to form the basic building blocks of the embryo. They then used an epigenome editor to target regions of the genome known to be involved in early development and control which genes were activated to induce the types of cells needed for early development. This approach allowed different cell types to “co-develop” naturally, closely resembling normal embryo formation compared to chemical approaches used in other studies. It also allows the cells to “establish that history of being neighbors,” Shariati said. “We do not change their genome or expose them to specific signaling molecules, but rather activate the existing genes.”
When they analyzed the embryoids, the scientists noted that 80% of the stem cells organize themselves into a structure that mimics a basic embryo after a few days. Most had undergone gene activation that reflects the development process that occurs in living organisms. In fact, the cells needed “very little input from us—it’s as if the cells already know what to do, and we just give them a little bit of guidance,” Shariati said.
Furthermore, the cells showed a collective behavior in moving and organizing together. “Some of them start doing this rotational migration, almost like the collective behavior of birds or other species,” Shariati said. “Through this collective behavior and migration they can form these fascinating embryonic patterns.”
Access to epigenetic editing tools was essential for getting these results. Scientists were able to both activate genes at the beginning of the experimentation process and also modify genes important for other parts of development. This allows the embryo models to be “programmable,” meaning they can be relatively easily tuned to test the impact of multiple genes as the embryo model develops. For Shariati, “this is the pioneering work of this study—the programmability and that we don’t rely on extrinsic factors to do this, but rather have a lot of control inside the cell.” He and his colleagues are interested in how the approach used here might be applied to better understand development in other species without using their actual embryos.