p63-Dependent Checkpoints in Oocytes

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Meiosis in the female germline of mammals is marked by an exceedingly prolonged arrest in meiosis I between homologous chromosome recombination and ovulation, which in humans can last five decades. During this arrest period, oocytes are highly vulnerable to DNA damage from endogenous, environmental, or therapeutic origins. How DNA damage triggers the death of these arrested oocytes is poorly understood but we now know that p63, a homolog of the p53 tumor suppressor, is highly expressed in these oocytes and plays an essential role in their death following exposure to ionizing radiation. These findings, based on mouse gene knockout models, have raised fundamental questions regarding the strategies to balance female fertility with the need for preventing mutations in a limited pool of oocytes. These questions are addressed in two specific aims. Aim 1 is to determine if p63 also functions to eradicate oocytes damaged by the highly mutagenic steps of homologous chromosome recombination. We also want to determine if TAp63 also contributes to oocyte death in young women undergoing chemotherapy for cancer. Our preliminary data for Aim 1 support the concept that TAp63 functions both in a post-pachytene checkpoint and in oocyte death due to chemotherapeutic drugs linked to ovarian failure. In this aim we will assess the ability of TAp63 null mutations in mice to rescue oocyte death that accompanies meiosis in the absence of key genes such as ATM, DCM, MHL, and SPO11 using specific mouse mutants. Aim 2 is to identify the transcriptional targets of TAp63 protein in oocytes following lethal and sub-lethal doses of ionizing radiation, chemotherapy, and homologous chromosome recombination. Our preliminary data strongly implicates the proapoptotic Puma gene in oocyte death, and the role of this gene in oocyte death will be probed in mouse knockout models. We anticipate that these studies will reveal much about how the oocyte maintains a high degree of genomic fidelity, how chemotherapy leads to female infertility, and insights into how the p53 family acts to eliminate cells with DNA damage to promote tumor suppression.