Researchers from the Babraham Institute’s Epigenetics Research Program have been able to learn more about nave stem cell reprogramming following a genome-wide functional screen. Their research, published today science advanceDescribes important regulators of reprogramming and provides opportunities for a more efficient, faster way to generate human nave pluripotent stem cells.
Human pluripotent stem cells (PSCs) are a useful tool for researchers who investigate how cells specialize in making up every tissue in our bodies. They come in two different states, primed and naive. Both types of PSCs can self-renew and differentiate into new cell types but they have different functions and molecular characteristics.
Group leader Peter Rag-Gun explained the importance of these cells: “Human PSCs in the nave state replicate key molecular and cellular characteristics of cells in the pre-transplantation stage embryo. Importantly, when nave PSCs are engrafted on their own under particular conditions. When these cells are encouraged to settle, they form structures that resemble the early blastocyst stage of development. By growing these cells in the laboratory, we can learn about key events that occur during human development, And they have potential uses in personalized medicine. But we need to create high-quality, stable stem cell populations to be able to do our experiments.”
Pluripotent stem cells are either formed from embryos or use Nobel Prize-winning methods to remove cell identity from specialized cells. Most reprogramming experiments generate primed PSCs, which are more developmentally advanced than nave PSCs. Nave PSCs can be collected directly from human pre-transplantation embryos, or more commonly researchers expose primed PSCs to conditions that induce them to become nave PSCs. Current methods for reprogramming were inefficient and slow, preventing researchers from producing high-quality stem cells numbers quickly.
Adam Bendl, PhD student and a lead researcher on the study, said: “Little was known about the requirement of genetic and epigenetic factors for naive cell reprogramming, and this knowledge gap limited the design of reprogramming conditions.”
The low efficiency of nave reprogramming suggests the presence of barriers that limit cells to access the nave state. Adam and his colleagues honed in on these hurdles by performing a large-scale genetic screen to identify genes and help reprogramming them. They were able to identify a large number of genes that have important roles in programming nave PSCs that were not previously associated with this process.
The team specifically focused on an epigenetic complex, the pRC1.3 complex, which regulates gene expression without altering the underlying DNA sequence, and which they found to be essential for the formation of nave PSCs. Without this complex, cells undergoing reprogramming become a completely different cell type instead of nave PSCs. This suggests that the activity of PRC1.3 may encourage more cells to reprogram properly to reduce inhibition.
After identifying factors that promote reprogramming, the researchers also looked at factors that inhibit reprogramming, exemplified in their study by an epigenetic protein called HDAC2. Dr. Amanda Collier, first author on the paper, explained: “Excitingly, when we selectively inhibited one of these factors using chemicals, naive PSC reprogramming occurred more efficiently and rapidly. We could see it from both sides. We can remove the barriers and introduce factors that push cells towards state change.”
This research not only improves the ability of scientists to produce human nave PSCs, it provides details on the molecular events occurring during cell state transition, some of which are conserved in developmental regulation in the human embryo.
The Rag-Gun Lab is putting together the pieces of a bigger puzzle – the best understanding of the formation and control of nave stem cells. His previous research has identified molecular factors that help maintain cells in a nave state. Group leader, Peter Rag-Gun, said: “By building our tools to manipulate pluripotent stem cells, we can spend more time asking important questions about pre-implantation embryos. In the long term, nave Further improvements in working with PSCs may open up the possibility of using these cells in personalized disease models or cell therapy, although this will require more research on how to differentiate nave PSCs into specialized cell types.