Researchers in a joint study between the University of Wisconsin, Madison, and the University of California, San Diego, have developed the first-ever method for tracking single blood stem cells in a living organism and mapping the cell’s architecture, which is expected to help scientists with blood disorder and cancer treatment development.
The study was co-authored by Owen Tamplin, an assistant professor in the Department of Cell and Regenerative Biology, of UW, Madison, and Mark Ellisman, a neuroscience professor at UC, San Diego, who recognized the need to expand the limited view of stem cells scientists have depended on thus far. Tamplin cites the low-resolution imaging and limited number of markers available with current stem cell imaging as chief issues limiting the information available to researchers.
“Transplanted blood stem cells are used as a curative therapy for many blood diseases and cancers, but blood stem cells are very rare and difficult to locate in a living organism,” Tamplin says. “That makes it very challenging to characterize them and understand how they interact and connect with neighboring cells.”
However, the new methods developed by Tamplin’s and Ellisman’s team provides high-resolution imaging of the stem cell as well as the surrounding niche microenvironment found within bone marrow and other tissues that contain stem cells. The researchers worked for more than six years to create imaging techniques that would allow them to follow the development of blood stem cells and explore the niche where difficult to track and understand interactions occur between these stem cells and their neighboring cells. Ultimately, the team used confocal and X-ray microscopy in addition to serial block-face scanning electron microscopy to examine cell-cell interactions.
Tamplin explains, “This [technique] has allowed us to identify cell types in the microenvironment that we didn’t even know interacted with stem cells, which is opening new research directions.” Among those cell types identified was dopamine beta-hydroxylase positive ganglia cells, a previously uncharacterized cell type in the niche that is crucial to improving therapies.
Zebrafish larvae were used for the study due to their transparent nature, which allowed the researchers greater visibility of the blood stem cell niche. Within the zebrafish, the team could see the arrival of a stem cell via circulation before it attached to its niche. The imaging techniques developed by the research team allowed for real-time tracking of a blood stem cell, and using electron microscopy, they could zoom further in on a cell.
“First, we identified single fluorescently labeled stem cells by light sheet or confocal microscopy,” Tamplin says. “Next, we processed the same sample for serial block-face scanning electron microscopy. We then aligned the 3D light and electron microscopy datasets. By intersecting these different imaging techniques, we could see the ultrastructure of single rare cells deep inside a tissue. This also allowed us to find all the surrounding niche cells that contact a blood stem cell. We believe our approach will be broadly applicable for correlative light and electron microscopy in many systems.”
By providing a better understanding of the behavior and functions of stem cells, the researchers hope their research, in turn, will help spur on the creation of improved stem cell-based therapies.