It is a universally acknowledged truth that a woman's supply of egg cells is finite. This is why scientists from Carnegie Institution for Science are developing a mechanism by which the body tries to eliminate egg cells with the poorest quality to ensure the top quality of genetic material. The results of the study done by Marla Tharp, Safia Malki, and Alex Bortvin are published by Nature Communications.
According to Bortvin, there are organisms that produce a large number of offspring may of which do not survive until adulthood. To make up for the loss, females of these species continually produce new cells throughout their reproductive lives. However, this is not the case with mammals which are adapted to producing limited offspring and have a fixed supply of egg cells. Bortvin narrates that because of this, each egg cell is precious and in need of quality control to be able to ensure the wellbeing of the children.
There are at least 80% of a female mammal's original pool of potential egg cells eliminated during the process called fetal oocyte attrition which happens during the development of the fetus. This process is observed and conserved in all studied mammals and although the origins of this phenomenon are clear, why it happens and everything else is still kept under the dark. This is the main target of the research behind this project, to focus on egg cells with a reduced quality.
In a prior study conducted by Bortvin and Malki, it is shown that the elimination of potential egg cells during fetal development is directly related to a transposable element called LINE-1 or the jumping gene. This jumping gene is originally discovered by biologist Barbara McClintock around the DNA of a cell, breaking genes and sometimes introducing genetic innovations that can improve the survival of the species. Bortvin and his colleagues were able to demonstrate how the jumping genes were quashed during sperm production but not during the development of egg cells.
The team has this theory that by purging the cells with the greatest activity of the LINE-1 will allow the selective survival of immature eggs that have the potential -- the lowest potential -- of succumbing to these jumping genes. Previously, Malki and Bortvin were able to discover that AZT can temporarily prevent the death of immature egg cells. Azidothymidine or more commonly known as AZT is the drug used to block the multiplication of HIV and LINE-1 and according to the observations, there is more than one mechanism to detect and eliminate the egg cells with excessive jumping gene activity.
With this in mind, the team is using AZT and applied it to mice that have no checkpoint kinase 2 protein (Chk2) in its system. Chk2 is the one responsible for the detection of damages in the DNA and repairs or marks the damaged genetic material. The researchers observed an increase in the reserve of egg cells in mice when AZT inhibited the jumping gene. Tharp explains that the shutting off of the fetal egg cell elimination process did not decrease the fertility in mice. "This provides further evidence that this is a quality control process to try to maintain the caliber of the egg supply," she said.
