Researchers discover how to purify human neural stem and progenitor cells and map their further development in the brain

April 18, 2023

How can you study king salmon if you can’t tell them apart from any other fish? How can you study a particular kind of cell if you can’t distinguish it out from other cells? Scientists are praising recent research by Irv Weissman and his colleagues at the institute as a “tour de force” that gives researchers the ability to identify and trace the development of all important neural stem and progenitor cells that give rise to the human brain. The technique promises to open a door to fully understanding human brain development, and may offer new avenues for studying brain disorders.

The research, published in the journal Cell, has already resulted in the characterization of a functionally distinct cell type that was previously unknown. Irv Weissman, MD, is the senior author on the paper. MD/PhD student Daniel Liu is first author on the paper. 

“Being able to separate cell types is central to biology,” Liu said. “In the mouse, we can use techniques like genetic lineage tracing to map cell development, but this requires genetic modification of cells in a growing brain, and of course in humans we can’t do that.”

“While most human neural cell types were known, there weren’t good ways of purifying those cells,” Liu said. “Without such purification methods, we will always be studying mixtures of different cell types.”

The researchers started with mid-gestational brain cells and looked for the presence or absence of a number of cell surface markers. They also analyzed the cells’ RNA activity. The investigators then took these characterized cells, transplanted them into mouse brain, and watched how they developed. By matching surface markers and RNA activity with developmental outcomes of the various cells, they were able to tell which markers were truly important in identifying various neural stem and progenitor cells, as well as map their respective developmental lineages.

“This method is powerful because we were able to identify purification schemes for all cell types in one go,” Liu said. “For every single cell type, we were able to show their lineage hierarchy as well as their transplant potential in a systematic way.”

One particular surprise that came out of the research concerned neural progenitor cells with high levels of the protein Thy1. Previously, such cells were thought to develop into neurons, but Weissman and colleagues found a subset of these cells that would develop into oligodendrocytes but not into neurons. 

The work is proof-in-principle that this method could ultimately be applied to create a complete scheme for the development of all brain cells from the very first neural stem cells to the most mature and differentiated neural cells. Such a well-defined developmental tree has been mapped out over decades for human blood and immune cells, and has proven immensely valuable for studying blood and immune disorders. A well-defined map of human brain cell development would also be hugely beneficial, the researchers say.

“There are several surprises that come from this study”  said Weissman. “First, we could study the properties of these cells by transplantation into newborn immune deficient mouse brain lateral ventricles; the human stem cells migrated to the mouse ‘home’ for brain stem cells, then accurately produced all brain lineages by site appropriate events.” This implies that despite over 85 million years of evolution between mice and humans, the signals for neurodevelopment in the brain were conserved, Weissman said 

“Now the transition to postnatal and adult neurogenesis by stem cells needs to be worked out so that we and others can begin to trace their activities in the human adult brain to find out how such cells change in human brain diseases,” Weissman said.

This study presents a method of achieving that well-defined map of human brain development, but there is still a lot of work to be done, the researchers say. “We have identified several more candidate markers that may further resolve heterogeneity in the hierarchy of human neural development,” Liu said. “That is something that will be the focus of future studies."

Liu says. “Being able to characterize and isolate all the various kinds of cells in the developing human brain will be a huge boon for studying brain function and disfunction, as well as help us develop clinically feasible brain stem cell transplants.”

Other Stanford scientists involved in the research were Joy He, Rahul Sinha, Anna Eastman, Angus Toland, Maurizio Morri, Norma Neff, Hannes Vogel and Nobuku Uchida.

This work was supported by the National Institute of Health (R35-CA220434T32-GM007365 and T32-GM145402), the Virginia and D.K. Ludwig Fund for Cancer Research and the CZ Biohub.