Quality control in oocytes by p63 is based on a spring-loaded activation mechanism on the molecular and cellular level

Mammalian oocytes are arrested in the dictyate stage of meiotic prophase I for long periods of time, during which the high concentration of the p53 family member TAp63α sensitizes them to DNA damage-induced apoptosis. TAp63α is kept in an inactive and exclusively dimeric state but undergoes rapid phosphorylation-induced tetramerization and concomitant activation upon detection of DNA damage. Here we show that the TAp63α dimer is a kinetically trapped state. Activation follows a spring-loaded mechanism not requiring further translation of other cellular factors in oocytes and is associated with unfolding of the inhibitory structure that blocks the tetramerization interface. Using a combination of biophysical methods as well as cell and ovary culture experiments we explain how TAp63α is kept inactive in the absence of DNA damage but causes rapid oocyte elimination in response to a few DNA double strand breaks thereby acting as the key quality control factor in maternal reproduction.

DOI:http://dx.doi.org/10.7554/eLife.13909.001

The irradiation and chemotherapy drugs that are used to destroy cancer cells also damage healthy cells. Germ cells – from which egg cells and sperm cells develop – are particularly vulnerable as they contain sensitive quality control mechanisms that kill any cell that contain damaged DNA. Consequently, after surviving cancer many patients are confronted with infertility.

A protein called p63, which is closely related to another protein that suppresses the formation of tumors, plays an essential role in detecting and responding to DNA damage. In immature egg cells (also known as oocytes), p63 mostly exists in an inactive form. The protein then switches to an active form when DNA damage is detected to trigger the process of cell self-destruction.

Now, Coutandin, Osterburg et al. have performed a range of biochemical, biophysical and cell culture experiments to study how p63 is kept in its inactive form in the oocytes of mice. The experiments showed that in the inactive form, the two ends of the protein form a sheet that closes a key site on the protein and prevents it from changing into its active form. However, this closed form can be thought of as being like a spring-loaded trap – it doesn’t take much energy to spring the trap and open the protein into its active form. Once this change has occurred, it is irreversible.

Coutandin, Osterburg et al. also found that the oocytes of mice already contain all the proteins necessary to activate p63. This means that once the switch to the active form is triggered there is no delay waiting for other proteins to be made, which makes oocytes extremely sensitive to DNA damage. Further work is now needed to investigate the exact molecular mechanisms behind the activation of p63.

DOI:http://dx.doi.org/10.7554/eLife.13909.002