Researchers at Cornell University in Ithaca, New York, have found a way to reverse the damage done to the immature eggs (oocytes) of female mice exposed to radiation. The research team hopes its discovery will lead someday to a way to restore fertility to women who become infertile as a result of cancer treatments involving chemotherapy or radiation.
The researchers targeted a process called meiosis, a form of cell division that occurs when eggs and sperm are created. During meiosis, a pair of chromosomes from the father are swapped with chromosomes from the mother. This swapping, or recombination, requires the double-strand DNA from each parent to break. It also ensures healthy genetic diversity.
When the broken DNA strands recombine in error or fail to recombine, miscarriage can occur and so can chromosomal disorders such as Down syndrome. In women, a protein called Chk2 (checkpoint kinase 2) destroys immature eggs damaged this way so no faulty DNA is passed forward to a woman’s children.
The Chk2 culls the defective eggs in a form of reproductive quality control so only healthy eggs are allowed to mature and potentially create a healthy baby.
Exposure to radiation can damage the oocytes in a similar fashion, resulting in infertility.
The Cornell study involved mice bred for a gene variation called Trip13, which is known to interrupt the recombination process, resulting in damaged eggs and sperm cells for use in the study. They then manipulated the activity of the Chk2 gene so that it did not cull the faulty sex cells. When the damaged immature eggs were left in place, many of them eventually repaired themselves to a restored level of viability. All the offspring born from these rescued eggs were normal.
Now that the research team has identified Chk2 as the gene responsible for ridding defective eggs, it hopes further research will lead to the ability to turn off Chk2 when a woman undergoes fertility-threatening cancer treatments. This effort of buying time may give her body the ability to repair the damage done by the cancer treatments and restore her fertility once treatments end.
Although similar experiments were done with sperm cells, turning off the expression of the Chk2 gene did not produce the same restorative effect in the sperm cells.
Source: Ramanujan, Krishna. “Protein that culls damaged eggs identified, infertility reversed.” Cornell Chronicle. Cornell University. Jan 30, 2014. Web. Feb 6, 2014.