According to a recent article in Horizon, the World Health Organization estimates that every one couple out of ten is dealing with fertility issues.
The long-held assumption has been that miscarriages or conceiving a baby with some type of genetic condition was more likely after the age of thirty-six. That theory has been replaced with the hard facts that chromosome and DNA abnormalities are found in about twenty percent of young women in their early to mid-twenties. By the time they are about thirty-six, these genetic errors become visible to physicians.
The ChromOocyte Project
Dr. Agata Zielinska is a cell biologist at the Max Planck Institute in Gottingen, Germany. Dr. Zielinska is part of the ChromOocyte team whose goal is to understand how the human egg reaches maturity.
This, in turn, will lead to knowledge at the cellular level and enable the researchers to eliminate the chromosome errors in the egg cell.
Between fifty to seventy percent of older human eggs (oocytes) are found to have chromosome or DNA errors.
About Trisomy Fetuses
Even though a certain number of cells may all come from one of the fertilized eggs, they may not all possess the same exact number of chromosomes.
For example, about one percent of Down syndrome cases involve two cell lines. One of the cell lines will be normal but the other cell line will have an additional chromosome 21 (trisomy 21).
The Team’s Unprecedented Study of Meiosis
The study began in the UK and was continued in Gottingen. The unprecedented accomplishment involved using high-resolution cameras to study live human egg cells just prior to fertilization as the cells proceed to meiosis.
Meiosis culminates in the fertilization of a mature sex cell (gamete). Fertilization is successful when a split egg, having left the ovary and formed new cells, cuts its own DNA in half. It then connects to a sperm cell that also cuts its own DNA.
The team was also able to capture details of chromosome deterioration and observe genetic errors.
Scientists suspect that cohesin, a cell component, plays a part in the chromosomal faults that arise in an oocyte.
Cohesin, a protein complex, is responsible for keeping other chromosomes together until such time as the egg divides its DNA just before fertilization.
In time cohesin loses its hold on the chromosome and falls away. This leaves the chromosome in a state of degradation.
Dr. Kikue Tachibana, a team leader, is zeroing in on interventions that will prevent separation errors at meiosis. Dr. Tachibana said that the team is investigating how cohesin deteriorates in order to gain insight into the events that trigger oocyte aging.
About Genetic Reprogramming
Another mystery has been partially solved by Dr. Tachibana and the team. It involves the reorganizing of DNA.
The questions center around paternal DNA and the errors that can occur during reorganization in the fertilized egg.
Post fertilization, the embryo undergoes genetic reprogramming and is transformed from either a sperm or an egg into a whole organism.
Dr. Tachibana theorized that the tears she observed in paternal DNA are actually essential to the reprogramming process.
The team, using mouse oocytes, discovered that the fertilized egg has a surveillance system that captures the entire process. Dr. Tachibana emphasized that unless the tears are repaired, the development of the fertilized egg will not continue.
The link between reprogramming and aging has not been investigated. Dr. Tachibana reasoned that an older oocyte plus an older sperm would create an inefficient mechanism.
The team has made significant progress but there is still much more work to be done.