October 14, 2011

Embryonic Stem Cells Behave Differently in a Dish

(Ivanhoe Newswire) — Can researchers predict the future of stem cells by knowing how they begin?  Dr.Thomas Zwaka, associate professor in the Stem Cell and Regenerative Medicine Center at Baylor College of Medicine, and his colleagues examined the cells of mice and showed that laboratory-grown cells express a protein called Blimp1, which represses differentiation to specific or regular tissue cells during germ cell development.

Embryonic stem cells exist only a day or two as they begin the formation of the embryo itself, then they are gone.

In the laboratory dish, however, they act more like continuous stem cells, renewing themselves and exhibiting the ability to form cells of almost any type.

Studies of these cells show that they also express other genes associated with early germ cell specification.

"It is quite a surprise that we have them. In the embryo, there is a mass of cells that eventually form the embryo, but they do not persist. They do not have a program built in that allows them to persist, "Dr. Zwaka , who is also part of the Center for Cell and Gene Therapy at BCM, Texas Children's Hospital and The Methodist Hospital, was quoted as saying.

Understanding what happens early in development of embryonic stem cells in the laboratory might help make the process of growing them, along with another new kind of stem cell called induced pluripotent stem cells — cells with the potential of becoming many different kinds of tissues that are derived from somatic or adult cells.

"These induced pluripotent stem cells are poorly understood," Dr.Zwaka was quoted as saying. "If we know what is happening when we derive embryonic stem cells in the laboratory, it will inform us when we make induced pluripotent stem cells. The end product is similar."

Zwaka was quoted as stating that the process of making the induced pluripotent stem cells is noisy and random.

"Every time, the clones look different and emerge at different time points," Zwaka was quoted as saying. By contrast, embryonic development is like clockwork, with events occurring at the same point with each embryo. However, development of embryonic stem cells in the laboratory becomes more disorganized as time goes on.

In the laboratory dish, the mouse embryo continues to develop at a fairly organized rate for two or three days, but when the single cells are separated and grown singly, the embryonic stem cells begin to emerge. Only tiny subsets, roughly 1 percent, of the cells become an embryonic stem cell in the laboratory.

The cells from the embryonic stem cells resemble early germ cells, the source of eggs and sperm.

"It seems that these seeming germ cells are the cells that make the embryonic stem cells in culture," Zwaka was quoted as saying.

In the embryo, the germ cells are able to become many different kinds of cells.  Furthermore, they have a way to prevent themselves from becoming specific tissue cells.

"They retain their primitive state, "Zwaka was quoted as saying.

In the future, he said, he hopes that investigators in both fields can collaborate and learn from one another.

SOURCE: Current Biology, published online October 13, 2011