"Seeing the colonies was heartening evidence of reprogramming, but not proof of ground state of pluripotent stem cells," Ming says. "We had to go through a series of characterization process, which generally takes about six months or more, depending on your rigor, to prove that.
The team then conducted a series of tests to verify not only that the genes they used to introduce the reprogramming factors were undetectable from the transformed cells, but also to prove their pluripotency. First, they confirmed that these cells could generate differentiated cells from all three germ layers the endoderm, mesoderm and ectoderm which eventually give rise to all of an animal's tissues and organs. By changing the recipe of the culture media in which the cells were growing, the team coaxed the cells to become not only neurons, but also fat cells and bone and muscle tissue, for instance. To confirm these were bona fide iPS cells with the ability to differentiate into all different cells types, the researchers performed a stringent test that involved injecting the presumed stem cells into mice whose immune systems were suppressed and noted that cells from three germ layers were present in the tumors that formed.
"The hard work of generating and characterizing these iPS cells is a prelude for future studies," Ming says. "Now, we can look at neural cells differentiated from these iPS cells in order to investigate the mechanisms and functions of the DISC1 gene in the nervous system, and understand the role it may play in diseases such as schizophrenia. These future studies may lead to the identification of new molecules that might serve as drug targets."
|Contact: Maryalice Yakutchik|
Johns Hopkins Medical Institutions