Genetic and Epigenetic Programs in Human Embryos
Each year, a team of physicians and staff from Pacific Fertility Center attend the Pacific Coast Reproductive Society (PCRS) annual meeting in Palm Springs, CA. One of the best talks of this conference was given by Dr. Renee Reijo Pera, Professor and Director of the Center for Human Embryonic Stem Cell Research at Stanford University. This was the second year in a row that Dr. Reijo Pera spoke at this conference and she continues to stimulate us with her exciting research. This year she her talk was entitled “Genetic and Epigenetic Programs in Human Embryos.” Her work involves mapping the first six days of human embryonic life. This is a visual map, a genetic map, and a molecular map. Visually, she is filming and analyzing time-lapse images of human embryos in the incubator and has been able to correlate various parameters of how cells divide with the probability that the embryos will make it to a full blastocyst stage by day 5-6 of culture. This has important implications for in vitro fertilization treatment and in the future will allow us to select early on which embryos will likely progress to successful implantation. She has been able to show in preliminary experiments that if the timing of early cell divisions does not follow a specific pattern, those embryos are much more likely to contain an abnormal number of chromosomes. Human embryos also give off cellular fragments as they divide. Sometimes these fragments end up being reabsorbed by the embryonic cells. But these fragments can contain excess chromosomes and mitochondria that are leaving and re-entering the cells. Why this is happening remains to be discovered.
She has also been able to map the process of human embryos expressing their genes. By the 4-8 cell stage of life, human embryos have to “turn on” their own genes and start making their own proteins. They first do this by destroying the maternal RNA (DNA messages) that originally came from the maternal genes in the egg. Then the embryo’s own DNA starts to make its own RNA messages. This finally ends with embryonic proteins being produced in embryos that are viable. Poorer quality embryos and those with chaotic, abnormal chromosome rearrangements are unable to do this properly and stop dividing.
It’s really only by scientists performing some of this essential work on early human embryos that we are going to be able to understand why some embryos make it and some don’t. And it is this understanding that is going to help us to select those embryos most likely to become a healthy human.
- Carolyn Givens, M.D.