Finding the Founder Cells: Determining the Origin of Pluripotency In Vitro

In the lab, stem cells begin their life in a cell culture dish by first assembling into organised colonies. This particular colony architecture is re-established every time the cells are subdivided and expanded. However, why and how this occurs has been a mystery, until now.  Recently published research involving ARMI scientists has found a distinct subset of cells that initiate, preserve and establish pluripotent stem cell cultures.

Collaboration is the cornerstone of making scientific discoveries and the heart of this research truth has been exemplified by the paper “Human Pluripotency Is Initiated and Preserved by a Unique Subset of Founder Cells,” recently published in the journal Cell. The project has involved a research team based in Canada, led by Professor Mickie Bhatia, as well as ARMI scientist Dr Kathryn Davidson and ARMI group leader Professor Andras Nagy.

In a cell culture dish, stem cells self-assemble in organised clusters with specific colony architecture that re-establishes every time the cells are subdivided and expanded. However, our understanding of the mechanisms and molecular mediators of this factor was lacking, until now. Research published in this paper demonstrates that there is a unique and distinct subset of  “founder” cells that initiate, preserve and establish pluripotency of stem cells cultured in vitro.

“This research has important implications on how we identify and characterise pluripotent stem cells in the lab, and on how we use these cells in experiments to understand development,” said Professor Nagy.

In addition to discovering these founder cells, Professor Bhatia’s group, which spearheaded the study, also found that this population expressed a certain protein on the cell surface, N-cadherin, which allows them to be isolated for further study and tracked in culture. As this protein is not expressed on mouse pluripotent stem cells, researchers wanted to know whether it was a unique marker of primate founder stem cells. It was this question that led to the collaboration between Professor Bhatia and Professor Nagy.

“This research has important implications on how we identify and characterise pluripotent stem cells in the lab, and on how we use these cells in experiments to understand development.” – Professor Andras Nagy

With the assistance of Professor Nagy and Dr Davidson, Professor’s Bhatia group was able to obtain nonhuman primate stem cells generated from marmoset skin cells, allowing them to dig deeper. The research team went on to characterise these founder cells and discovered that they could be regulated by a critical signalling pathway, the non-canonical Wnt signalling pathway. This knowledge provides possible candidates for targeting for experimental purposes, while filling in some blanks in our understanding of the many roles specific signalling pathways play.

Another important finding in the paper highlighted the shared hallmark properties between these founder cells and the primitive endoderm, one of the three cell layers in an embryo. This link between these founder cells and the in vivo properties of the early developing primate embryo highlights the previously unappreciated origins and function of in vitro pluripotency.

“Considering how we use stem cell cultures in vitro as an important tool in regenerative medicine research, in human disease modelling, in drug screening, it’s critical we understand their origins, their behaviours and how their intrinsic properties may affect results. These findings help us to better interpret our research and helps us draw clearer lines to what is happening in human embryos,” added Professor Nagy.

This project demonstrates the high-quality research that is borne from international collaboration and demonstrates how ARMI is one of the global leaders in regenerative medicine. Congratulations to Professor Bhatia’s group, Dr Davidson, and Professor Nagy!

More information

Click here to read the publication: Nakanishi M, Mitchell RR, Benoit YD, Orlando L, Reid JC, Shimada K, et al. Human Pluripotency Is Initiated and Preserved by a Unique Subset of Founder Cells. Cell. 2019;177(4):910-24.e22.

Dr Kathryn Davidson is currently a Research Fellow in the Polo Group, led by Professor Jose Polo, though she continues to collaborate with Professor Andras Nagy and his groups at ARMI and in Canada. She was supported by an Endeavour Fellowship for this work. The Polo group is interested in the transcriptional and epigenetic mechanisms that govern cell identity and cell fate. It has a particular focus on pluripotency and the reprogramming of somatic cells into induced pluripotent stem cells and other mature cell types. For more information on Professor Jose Polo and his group at ARMI, please visit the Polo Group page. You can contact Professor Jose Polo via jose.polo@monash.edu.

At ARMI, the Nagy group is predominantly focused on developing cell therapies for brain injury, stroke and multiple sclerosis. For more information on Professor Andras Nagy and his group at ARMI, please visit the Nagy Group page. You can contact Professor Andras Nagy via andras.nagy@monash.edu.

This paper was led by Dr Mio Nakanishi and Professor Mickie Bhatia from McMaster University, Canada, with contributions by ARMI researchers and scientists from Harvard Medical School, US.