The five-year relative survival rate of cancer patients has improved from 50 to 68% in the last thirty years. The survival rate of pediatric cancers has reached 80%, and the NCI predicts that 1 out of every 250 adults will be a survivor of childhood cancer by 2015. As the number of cancer survivors increases, so does the concern for their quality of life post-treatment. One of the most serious problems associated with radiation and chemotherapy is the off-target effect on germ cells. For young women, this is a particularly serious concern because the immature oocytes that comprise the ovarian reserve are highly sensitive to chemo/radiation therapies. Since the ovarian reserve represents ALL the follicles available for future fertility as well as endocrine function, the loss of immature oocytes and subsequent sex steroid deficiency have significant physical and psychological consequences. The goal of this project is to better understand the mechanisms associated with survival and death of immature oocytes caused by cancer treatments, and in doing so, identify neo-adjuvant medical approaches for preserving fully functional ovaries in young women undergoing treatment. A recent breakthrough discovery by Gonfloni et al. demonstrated that the ovarian reserve could be protected against the chemotherapeutic drug, cisplatin, by co-administration of kinase inhibitor imafinib mesylate. Although its precise mechanism was not demonstrated, their study suggested that cisplatin-induced oocyte death was mediated by p63, a member of the p53 transcription factor family. Additionally, it was proposed that imatinib mesylate rescued oocytes from apoptosis by blocking activation of p63 by c-Abl. Our preliminary studies of p63-null oocytes confirmed the essential role of p63 in cisplatin induced death of oocytes. In addition, our studies suggested that the gene dosage of p53 and p63 determines the death/survival of oocytes. Moreover, p73, another member of the p53 family, was also highly expressed in oocytes undergoing apoptosis in response to cisplatin. Therefore, the overall hypothesis of this proposal is that the balance between survival and death of oocytes in primordial and primary follicles is controlled by the interaction between p53 family members, and thus the p53 family members are targets for fertoprotective agents. To develop safe and effective fertoprotective therapies, it is essential to elucidate the mechanism through which p53 family members are activated by chemotherapy. To advance our understanding, we have developed an assay system that consists of in vitro culture and subrenal grafting of mouse ovaries. We will dissect the molecular pathways involved in the death of immature oocytes by applying this assay system to genetically engineered mouse models. The results of these proposed studies will be critically important for understanding the mechanisms that underlie physiologic and iatrogenic follicle death and may reveal new strategies for protecting the fertility of young women diagnosed with cancer.