Germ cells are sensitive to genotoxins, and ovarian failure and infertility are major side effects of chemotherapy in young patients with cancer. Here we describe the c-Abl-TAp63 pathway activated by chemotherapeutic DNA-damaging drugs in model human cell lines and in mouse oocytes and its role in cell death. In cell lines, upon cisplatin treatment, c-Abl phosphorylates TAp63 on specific tyrosine residues. Such modifications affect p63 stability and induce a p63-dependent activation of proapoptotic promoters. Similarly, in oocytes, cisplatin rapidly promotes TAp63 accumulation and eventually cell death. Treatment with the c-Abl kinase inhibitor imatinib counteracts these cisplatin-induced effects. Taken together, these data support a model in which signals initiated by DNA double-strand breaks are detected by c-Abl, which, through its kinase activity, modulates the p63 transcriptional output. Moreover, they suggest a new use for imatinib, aimed at preserving oocytes of the follicle reserve during chemotherapeutic treatments.

Background Anti-cancer therapy is often a cause of premature ovarian insufficiency and infertility since the ovarian follicle reserve is extremely sensitive to the effects of chemotherapy and radiotherapy. While oocyte, embryo and ovarian cortex cryopreservation can help some women with cancer-induced infertility achieve pregnancy, the development of effective methods to protect ovarian function during chemotherapy would be a significant advantage. Objective and rationale This paper critically discusses the different damaging effects of the most common chemotherapeutic compounds on the ovary, in particular, the ovarian follicles and the molecular pathways that lead to that damage. The mechanisms through which fertility-protective agents might prevent chemotherapy drug-induced follicle loss are then reviewed. Search methods Articles published in English were searched on PubMed up to March 2019 using the following terms: ovary, fertility preservation, chemotherapy, follicle death, adjuvant therapy, cyclophosphamide, cisplatin, doxorubicin. Inclusion and exclusion criteria were applied to the analysis of the protective agents. Outcomes Recent studies reveal how chemotherapeutic drugs can affect the different cellular components of the ovary, causing rapid depletion of the ovarian follicular reserve. The three most commonly used drugs, cyclophosphamide, cisplatin and doxorubicin, cause premature ovarian insufficiency by inducing death and/or accelerated activation of primordial follicles and increased atresia of growing follicles. They also cause an increase in damage to blood vessels and the stromal compartment and increment inflammation. In the past 20 years, many compounds have been investigated as potential protective agents to counteract these adverse effects. The interactions of recently described fertility-protective agents with these damage pathways are discussed. Wider implications Understanding the mechanisms underlying the action of chemotherapy compounds on the various components of the ovary is essential for the development of efficient and targeted pharmacological therapies that could protect and prolong female fertility. While there are increasing preclinical investigations of potential fertility preserving adjuvants, there remains a lack of approaches that are being developed and tested clinically.

IntroductionStem cells are traditionally considered to be either multipotent (eg, embryonic stem [ES] cells) or restricted in their differentiation potential (tissue stem cells). Reports on "transdifferentiation" and the discovery of multipotent adult progenitor cells in bone marrow, brain, and muscle have recently challenged this view. [1][2][3][4][5] One central issue underlying the debate on developmental options of stem cells concerns the molecular mechanisms responsible for establishing and maintaining their transcriptional programs and decisions to differentiate. So far, few of the key regulatory genes active in stem cells and/or multipotent progenitors have been studied at the level of transcriptional regulation. [6][7][8][9][10][11][12][13][14][15][16][17] Identification and comparison of several such genes will provide important insights into the transcriptional programs of stem and multipotent progenitor cells.The Kit (White spotting locus) gene, encoding the transmembrane receptor of the cytokine stem cell factor/Kit ligand (KL), is an important regulator of proliferation/survival and/or migration of several stem cell types such as the primordial germ cells (PGCs), [18][19][20][21][22] the multipotent hematopoietic stem cells (HSCs), 20,23 the neural crest, and the intestinal Cajal cells. 20 Null mutations in the Kit or the KL (Steel) gene result in severe hematopoietic and germ cell defects and in utero or perinatal death, whereas mutations that diminish Kit tyrosine kinase activity or KL production affect mainly hematopoiesis and the development of germ cells, melanocytes, and the intestinal Cajal cells. 20 During mouse developmentKit is expressed at a low level in pluripotent inner cell mass cells (and in epiblast-derived ES cells in culture) 24,25 and, at relatively higher levels, in PGCs, early hematopoietic progenitors, and other cells. 25 In adults, Kit is expressed in a variety of cell types including HSCs, immature hematopoietic progenitors and mast cells, oocytes, a subpopulation of male germ cells, and melanocytes. [18][19][20][21][22][23]25 In the mouse embryo, hematopoietic progenitors are detected both extraembryonically in the yolk sac, after embryonic day 7 (E7), and intraembryonically, first in the para-aortic splanchnopleura and aorta-gonad-mesonephros (AGM) regions, then in fetal liver and vitelline vessels, [26][27][28] and finally in bone marrow. The earlier hematopoietic cells (primitive hematopoietic cells) are morphologically and biologically distinct from the later cells (definitive hematopoietic cells). Definitive hematopoiesis is seeded by HSCs, which arise intraembryonically in the AGM region and in the vitelline vessels around E11. [28][29][30] Immature precursors to definitive HSCs, however, have also been detected both intraembryonically 31,32 and in the yolk sac 32 at earlier stages of development. Murine PGCs first become visible around E7 in the extraembryonic mesoderm, then migrate through the allantois (E8) to the hindgut, from where they move to reach the gonadal ...

The development of follicles in the mammalian ovary involves a bidirectional communication system between the follicular cells and oocyte that is now beginning to be characterized. Little is known about the mechanisms underlying the beginning of the oocyte growth and the acquisition of the competence to resume meiosis by the growing oocyte. In the present study, we devised a multistep culture system for mouse oocytes obtained from 15.5- to 16.5-days postcoitum embryos (mean diameter +/- SEM, 9.7 +/- 1.3 microm), allowing three stages of the oocyte growth to be identified: (i) an early stage in which the oocyte growth is induced by direct stimulation of a soluble growth factor, namely stem cell factor (SCF), independent of the formation of gap junctions with granulosa cells; (ii) a second phase in which the oocyte growth depends on the combined action of SCF and contacts with granulosa cells; and (iii) a third phase of granulosa cell-dependent, SCF-independent growth. At each stage, key events of oocyte development and differentiation, such as the c-kit reexpression, the early zona pellucida assembly, and the beginning of follicologenesis, were observed to occur independently by the presence of SCF. At the end of the in vitro growing phases, lasting 18-20 days, oocytes reached a size (50 +/- 2.5 microm) and a chromatin differentiation (stage I-II) equivalent to those of 9- to 10-day-old preantral oocytes and were unable to complete the growth phase. About 50% of the in vitro-grown oocytes were induced to resume meiosis by okadaic acid (OA) treatment. However, a significant fraction of them (48%) showed inability to maintain the chromosome condensation in M-phase. When in vitro-grown oocytes were treated with UO126, a specific MEK inhibitor that prevents activation of mitogen-activated protein kinases (ERK-1 and ERK-2), for 1 h before, during, and following OA treatment, only 22% of oocytes underwent germinal vesicle breakdown after 24 h from the OA treatment. These studies demonstrate that SCF alone can induce the onset of the oocyte growth. This is, however, not sufficient to fully activate the mechanisms governing the acquisition of the meiotic competence previously described as a 15-day oocyte-autonomous clock starting at the onset of growth. The inability of oocytes to progress into the last stages of growth and the lack of synchrony between nuclear and cytoplasm maturation showed by a subset of them resemble the characteristics of oocytes from connexin-37- and -43-deficient mice and indicate the preantral/antral transition point as a critical stage of oocyte development requiring the coordinated differentiation of the oocyte with granulosa cells and the maintenance of adequate communication between these two cell types to assure the correct oocyte meiotic maturation.