Scientists in a Lab
ISCRM scientists use a step-by-process to change the identity of cells by returning adult cells to a stem cell-like state, then differentiating them into a different cell type.

Stem cells can become almost any kind of cell in the body. From an undifferentiated state, chemical, physical, and temporal cues signal stem cells to become almost any type of cell in the body. Scientists refer to this quality as pluripotency. Researchers working in labs differentiate stem cells into specific tissue types (e.g. neurons, heart muscle cells, kidney cells) to study human development, to understand how diseases begin, and to test potential drugs and other therapies. In some cases, such as transplant procedures for cancer, stem cells are even used to treat patients.

For many years, stem cells were often obtained from donated embryonic tissue. These embryonic stem cells have the blank-slate attributes that made them useful for research and many discoveries and treatments have resulted from embryonic stem cell research. However, embryonic stem cell research remains controversial and embryonic stem cells have particular limitations – for example, they cannot be matched to a specific patient.

By the turn of the 21st century, the quest had begun for a way to make non-embryonic stems cell work like  embryonic stem cells. In 2006, scientists led by Shinya Yamanaka at Kyoto University in Japan pioneered a new technology, known as induced pluripotent stem cells, or iPSC for short. This breakthrough allows scientists to take easily accessible cells (like skin or hair) and reprogram them. This approach is analogous to purchasing a used laptop and wiping the hard drive clean before loading with new software  – perhaps changing its identity from a business tool to a gaming device.

How Do Scientists Reprogram Cells?


Magnified image of a neuron grown from brain tissues of a patient with Alzheimer’s disease using a process known as transdifferentiation in which cells are programmed without being returned a stem cell-like state.

In his Nobel Prize-winning work, Shinya Yamanaka used molecules called transcription factors (proteins that carry instructions to targeted regions of DNA) to create a special line of cells that would emit a color-coded signal each time a gene was activated. While these genes are present in every cell in the body, they are only turned on in embryonic stem cells. Yamanaka showed that firing up the gene in non-embryonic cells would revert the cells to an embryonic-like state – an elegant workaround to embryonic stem cell research. The molecules his team identified are now known as the Yamanaka factors.

To return an adult cell to a stem cell state, scientists package a stretch of DNA (called a plasmid) that carries the reprogramming instructions with a solution of lipids that help it melt through the cell membrane and integrate into cells growing in cultures on plates. When the transcription factor binds to the targeted region of DNA, genes that make the cell a stem cell are turned on and genes that identify the cell as a specific type are turned off.

Early in the iPSC era, the transcription factors were delivered to the cells using a virus, which carried the DNA that instructed the cell to become a stem cell again. That system proved to be imperfect. Scientists found that bits of genetic material would become integrated into the cell, leading to unintended consequences later on. More recently, in a non-integrating approach, the DNA encoding the transcription factors is synthesized on a plasmid, a circular DNA construct that  is introduced with a  zap of electricity that opens up a temporary hole in the cell membrane. This allows enough of the factors to get in the cells, just long enough to complete the reprogramming process.

After a month, the colonies that best match the morphology of the desired pluripotent stem cells are selected and run through several tests so measure their stability and capability of becoming all three germs layers (endoderm, ectoderm, and mesoderm). At the end of the process, researchers have a colonies of cells that can become any tissue type of a human and help them ask and answer important questions that cover the spectrum from basic science to translational medicine.

Giving Cells New Identities


To give the cells new identities, the researchers take cues from developmental biology and apply them in a dish. Over the next several weeks, molecules – typically proteins, or chemicals that mimic proteins – will be introduced to the colony of undifferentiated cells. These molecules provide the same signals that turn on gene expression pathways in the womb, instructing cells to grow, divide, and differentiate into various cells types in all three germ layers.

Jessica Young
Jessica Young, PhD, uses neurons grown from other cell types to study the origins of Alzheimer’s disease.

This step-by-step process follows a similar biological sequence to the process that would unfold in a naturally developing organism. After several weeks of feeding the cells a specific diet of molecules, researchers will monitor the cultures as the nondescript cells begin to look and act like whichever cell type they are hoping to study. The cells that grow into viable mature cells become remarkably close proxies for neurons, heart cells, kidney cells, and other cell types.

“At this point we’ve arrived at a differentiated cell that for all intents and purposes has all of the functional properties of the cells that we normally wouldn’t be able to study because they’re inaccessible,” explains ISCRM faculty member Dr. Jessica Young, whose lab use neurons derived from induced pluripotent stem cells to investigate the onset of Alzheimer’s disease. “Because we can make a neuron in a lab, we can study the same degenerative processes that occur in the human brain. It’s not going to be a perfect match, but it’s very close.”

Right now, in ISCRM labs, reprogrammed induced pluripotent stem cells are being used to advance discoveries in multiple research areas, including Alzheimer’s disease kidney disease, heart disease, autism, and muscular dystrophy, and to explore the mysteries of early-stage human development.