EMBRYONIC STEM CELLS PROPERTIES BASIC INFORMATION

In the movie “Star Trek IV: The Voyage Home,” the crew of the Enterprise travels back in time to 20th-century Earth, and Dr. McCoy helps a woman undergoing dialysis. As she’s being wheeled down a hospital corridor, she joyfully tells everyone, “Doctor gave me a pill, and I grew a new kidney!”

Okay, that kind of biological miracle is still the stuff of science fiction. But embryonic stem cells hold enormous potential for giant leaps in medical treatments because of their unique properties:

✓ They can divide and grow more or less indefinitely.
✓ They can develop into any cell type found in the adult body.
✓ They have an incredibly lengthy shelf life, so they can be stored for very long periods without losing their potency.

Growing and growing and growing . . .
Left to their own devices, cells in the blastocyst eventually differentiate, or begin developing special characteristics of job-specific cells. Some become neurons, for example — the brain cells that control thought and movement.

Others spin off into red or white blood cells, or heart muscle cells, or liver cells, and so on. DNA, which provides the blueprints for cell development, and RNA, the user’s manual stating which part of the blueprint to follow, determine which job each cell takes on.

In the lab, though, scientists can delay the reading and implementation of the genetic instructions that tell cells to specialize by isolating the inner cells from blastocysts, transferring them to Petri dishes, and feeding them a mixture of appropriate nutrients (called a growth medium or culture medium) so they can
continue to grow.

Under the correct conditions, embryonic stem cells read the genetic instructions for self-renewal and continue to grow until they’re exposed to signals that tell them to read the genetic instructions for specialization.


Cells like to touch other cells, so scientists usually line the Petri dish with alayer of other cells — most commonly embryonic skin cells from mice that have been treated so they won’t grow. The cells in this layer are called feeder cells.

The inner cells from a blastocyst are placed on top of the feeder cells, and a growth medium (a broth rich in the nutrients the cells need to thrive) is added. Depending on what’s in the growth medium, these inner cells can continue dividing into more embryonic stem cells, or they can begin differentiating into specific categories or types of cells.

One of the risks associated with using mouse feeder cells to grow human embryonic stem cells is that the human cells may be infected with viruses or contaminated with other unwanted material from the mouse cells. Researchers have come up with other ways to grow embryonic stem cells, but only time will tell us whether these alternative methods are as useful and reliable as using mouse cells.

Assuming the relocation of the blastocyst’s inner cell mass into a Petri dish is successful — and that’s not always the case — the embryonic stem cells grow until they crowd the dish. Then they’re removed from the original dish, divided up, and placed into several new dishes with fresh growth media.

This process is called subculturing, and each round of subculturing is called a passage. Scientists can separate, freeze, and store batches of cells at any stage of the subculturing process. They also can ship them to other researchers after they’ve verified that the cells are stable and usable.

It takes at least six months and several passages to create an embryonic stem cell line — that is, millions of cells derived from the original inner cell mass of the blastocyst that meet two critical conditions:

✓ They retain their ability to grow into any kind of cell in the adult body.
✓ They appear to have no genetic defects.

Scientists use a method called karyotyping to make sure that stem cells have the correct number of chromosomes. Normal human cells have a total of 46 chromosomes, paired in sets of two; you inherit one of each set, or 23 chromosomes, from each parent.

Embryonic stem cells’ ability to grow and divide practically indefinitely under the right conditions is an important property for medical research and developing useful treatments. It takes millions of cells to conduct reliable experiments, and one of the biggest eventual challenges in in using stem cells to treat illness is creating enough of them to do the job.