Researchers from the Gladstone Institutes, USA, managed to obtain stem cells from skin cells, by activating just one gene in the cells using CRISPR technology. The innovative method, published on January 18, 2018 in Cell Stem Cell, offers a potentially simpler technique to produce the valuable cell type and reveals important information about the process of cellular reprogramming process.
“This is a new way to make induced pluripotent stem cells that is fundamentally different from how they’ve been created before,” – said author Sheng Ding, a senior investigator at Gladstone. “At the beginning of the study, we didn’t think this would work, but we wanted to at least try to answer the question: can you reprogram a cell just by unlocking a specific location of the genome? And the answer is yes.”
Pluripotent stem cells can be turned into almost any type of cell in the body, making them a key therapeutic resource for diseases that are not amenable to conventional treatment, such as heart failure, Parkinson’s disease, blindness, etc. IPSCs are also an excellent model for studying diseases and an important a tool for testing new drugs on human cells.
In 2006, Gladstone Senior Investigator Shinya Yamanaka, MD, discovered a method for producing induced pluripotent stem cells by treating ordinary skin cells with four key proteins. These proteins, called transcription factors, alter the expression of genes, turning off genes associated with skin cells and turning on genes associated with stem cells.
Basing on this work, Ding with colleagues previously created iPSC, using not transcription factors, but adding cocktails of chemicals to the cells.
In present study, they used one more method of converting skin cells into stem cells, artificially increasing the expression of transcription factors by using a CRISPR activation system based on the modified inactive Cas9 protein (dCas9). In this case, dCas9 was used to transport activator or repressor proteins to the desired region of the genome to control gene expression.
“Having different options to make iPSCs will be useful when scientists encounter challenges or difficulties with one approach,” – said Ding, who is also a professor of pharmaceutical chemistry at the University of California, San Francisco. “Our approach could lead to a simpler method of creating iPSCs or could be used to directly reprogram skin cells into other cell types, such as heart cells or brain cells.”
CRISPR is a powerful tool for targeted genome manipulation, aimed at a unique DNA sequence. Such a target sequence is either deleted, or replaced, or temporarily turned on or off.
The goal of Ding ‘s team was two genes, which are expressed only in stem cells and known to be integral to pluripotency: Sox2 and Oct4. Like transcription factors these genes turn on other stem cell genes and turn off those associated with different mature cell types.
The researchers found that using CRISPR, they could activate either Sox2 or Oct4 to reprogram cells. In fact, they demonstrated that it is sufficient to activate only one regulatory site of the gene in order to trigger the natural chain reaction that led to reprogramming the cell into an iPSC.
For comparison, four transcription factors are used in the standard procedure. What’s more, one transcription factor typically targets thousands of genomic locations in the cell and changes gene expression at each location.
“The fact that modulating one site is sufficient is very surprising,” – said Ding. “Now, we want to understand how this whole process spreads from a single location to the entire genome.”