TORONTO -
Scientists have made a breakthrough involving a method that turns stem cells a fluorescent green colour for study in the laboratory, which is like having a "spotlight" to help differentiate them from other cells.
They've managed to get the fluorescent green to turn off when the stem cells, sometimes described as the building blocks of life, go on to become nerve cells, according to Canadian research published Sunday in the journal Nature Methods.
Dr. James Ellis, the principal investigator of the study led by Toronto's Hospital for Sick Children, says researchers looking at thousands of cells on a petri dish normally try to recognize stem cells by the shape of the colony, which usually has a fairly rounded shape with a distinct edge for the human stem cells. Other cells are "sort of growing in a loose sheet," he explained.
"Without the colour you have to look across the entire plate looking for these distinct colony shapes and even then it ... sort of tells you that it could be a stem cell, but it might not be a stem cell colony, so you have to pick each of those colonies and work them up, and then do some tests on them to find out if they are stem cells."
Stem cells in their normal state don't really have a colour, and on a dish would appear "rather grey," said Ellis, co-director of the Ontario Human iPS Cell Facility at the hospital.
"When they turn green we can put them in the dark and we can find the green cells very easily. It's like having a spotlight on a person in a crowd in the dark, so you can go straight and find that person in that crowd."
The transformation from "rather grey" to green was achieved through the use of a green fluorescent protein gene that was originally isolated from jellyfish.
"You can put that into a virus and have it controlled in such a way that it will only turn on in stem cells," Ellis said.
The stem cells will continue to be fluorescent green as they divide, as long as they stay in the stem cell state.
"The wonderful thing about these stem cells is that we can use them to make any cell type of the body, so we could grow them up under certain conditions to make them become heart cells, and they would start to beat," Ellis said.
"The green gene is only going to be on when they're in the stem cell state. So once they become cardiac cells, the heart cells, they'll no longer be green."
Turning off the green was the "tricky part," he said.
"What we've done is there are parts of the DNA around the gene that control what cell type it's on. And what we've done is we've identified a combination of these elements that will control the genes so that it only turns on in stem cells."
In addition to using an element from a lab in Vancouver, Akitsu Hotta, lead author of the study and a post-doctoral fellow from Japan, realized some other elements called enhancers could be used, Ellis said, and the combination worked well.
The researchers have used the green technique already, taking skin cells from a patient with Rett's syndrome, an autism spectrum disorder, reprogramming them into the green stem cells and growing them into nerve cells.
It would be unethical to excise nerve cells from someone's brain, as it would expose the patient to risk.
This way, Ellis explained, researchers can study nerve cell maturation and the electrical transmission between nerve cells, and "that's never been possible in the human context before."
Another benefit to the green on-off switch is the fact that stem cells transplanted back into a mouse have a tendency to form tumours.
For a spinal cord injury, for example, doctors would want to take stem cells and make them into nerve cells and then transplant the nerve cells into the injured spine, Ellis said.
"But if you do that, you need to make sure there are absolutely no stem cells remaining that go into the spine as well because if there are any of those remaining, they may form tumours," Ellis said.
"So by having the stem cells being green, we can look to see, are there any green cells before we do a transplantation and try to make sure that tumours do not occur that way."
Dr. Michael Rudnicki, scientific director Stem Cell Network, said the research allows scientists to purify cells "mechanically and otherwise, and also to readily identify them."
"I think it's an important advance and it's one of the steps along the way that need to be taken to make this technology easily and readily usable in many laboratories around the world," he said from Ottawa.
The research was supported by the Ontario Ministry of Research and Innovation, the Canadian Institutes of Health Research, the Stem Cell Network, SickKids Foundation and the International Rett Syndrome Foundation and SickKids Restracomp Award.
