Presented by: Renee Reijo Pera, PhD
Director, Center for Human Embryonic Stem Cell Research and Education
Professor, Obstetrics and Gynecology
Stanford University Medical Center
- Unlike adult stem cells, embryonic stem cells have the potential to differentiate into any cell, including another stem cell
- Understanding the process of how two pronuclei (egg and sperm) fuse to become an embryo is crucial before new steps can be made in applying stem cells to health issues
- Embryonic stem cells may have particular impact on women because of their potential applications in reproductive health, fertility and fetal outcomes
One of the most perplexing, promising and problematic components of modern biomedicine arises in the earliest steps of embryonic development. Just a few days after an egg is fertilized, its divided cells form a blastocyst, the source of embryonic stem cells. Embryonic stem cells possess a nearly unlimited capacity for self renewal and the ability to differentiate into virtually any cell type of an organism.
“A stem cell is a cell that can make a decision,” said Renee Reijo Pera, PhD, director of Stanford’s Center for Human Embryonic Stem Cell Research and Education and a professor of obstetrics and gynecology. “It can choose to divide and make another stem cell or differentiate into a skin cell, a liver cell, a neuron or any other cell type in the body.”
Reijo Pera’s presentation of her work in developmental biology and the potential of embryonic stem cells at Arrillaga Alumni Center on May 8 was sponsored by Women’s Health @ Stanford, a multidisciplinary program that consolidates research, education, clinical care and advocacy to improve women’s health and well-being.
While adult stem cells from established lines and fetal stem cells (from aborted fetuses or miscarriages) are open to federal funding, embryonic stem cells remain the source of much political and ethical debate. However many researchers believe that embryonic stem cells have distinct advantages over other types of stem cells because they appear to be able to make any cell, can provide an endless supply of cells and are readily available. Adult stem cells can only form cells that duplicate their original tissue source.
One of Reijo Pera’s primary interests is using embryonic stem cells to better understand the very first days of embryonic development. “To me, there is nothing more exciting than the fact that sperm and egg come together to form an embryo,” she said. “And now we have the imaging tools to observe the process in amazing detail.”
Reijo Pera described the first days of human embryonic development, starting with the migration of the two pronuclei (the nucleus of the sperm and egg), which carry half the number of chromosomes and then fuse to create a new and unique combination of DNA.
“Day 1 sets all sorts of bars and standards,” she said. “Like a computer, the DNA is wiped clean and readied to start a new program.”
After two sets of cleavage division, the genome is activated, launching the start of a new genetic combination. By Day 5 the cells compress into a blastocyst containing outside cells that will eventually attach to the uterus and an inner cell mass that is the source of embryonic stem cells. About a week later, cells called epiblasts fill up along the inside walls and start to differentiate, losing the intrinsic ability to develop into all cell types. These differentiated cells become:
- Ectoderm: the start of tissue for hair, skin and neurons
- Mesoderm: for heart, bones, connective tissue and muscle
- Endoderm: for the digestive system and respiratory tract
“We know more about cell signaling than we do about human development. That lack of understanding is a source of much of the controversy around embryonic stem cells,” said Reijo Pera. “It’s critical that we realize the core value of human development because it is what makes us uniquely human.”
In addition to her work understanding early human development, Reijo Pera is looking at ways to develop new embryonic stem cell lines from in vitro fertilization blastocysts. This work could reveal ways of differentiating embryonic stem cells into eggs that could eventually be used as an alternative to eggs donated by women.
Her research is looking at ways to take normal tissue cells and reprogram them into cells with the same unlimited properties as embryonic stem cells. Reijo Pera said this work could lead to a better understanding of infertility and common birth defects.
“This a very exciting time for studies in human developmental genetics,” she said. “Women, in particular, should care about stem cell biology because of the incredible impact it may have on reproductive health, pregnancy and assisted fertility.
For example, she said, of the 74,000 women who have an embryo transfer, only 31,000 result in pregnancy and about one third (25,000) result in live birth delivery.
“We can do better,” she said. “This is a precious resource, and we need to practice good stewardship.”
While much of the promise of stem cells, such as cell replacement therapy and tissue regeneration, lies in the future, Reijo Pera said that in the near term understanding their biology can be used to define a healthy embryo, leading to fewer birth defects; to detect early signs of diseases like Alzheimer’s; and to improve treatment for cancer and neural disorders.
About the Speaker
Renee Reijo Pera, PhD, is a professor of obstetrics and gynecology and the director of Stanford’s Center for Human Embryonic Stem Cell Research and Education. She was a the co-director of the Human Embryonic Stem Cell Center at the University of California at San Francisco before joining the Stanford faculty in 2007. One of Newsweek‘s “20 Influential Women in America” in 2006, Reijo Pera is an expert in embryonic stem cell research and the genetics of egg formation. She received her BS in biology from the University of Wisconsin, an MS in biology from Kansas State University, her doctorate in molecular cell biology from Cornell, and she conducted her postdoctoral studies in human genetics at the Whitehead Institute at MIT.
For More Information:
Stanford Institute for Stem Cell Biology and Regenerative Medicine
California Institute for Regenerative Medicine
National Institutes of Health