Commuting the death sentence: how oocytes strive to survive

The importance of folate, zinc and antioxidants in the pathogenesis and prevention of subfertility

Current treatments of subfertile couples are usually empiric, as the true cause of subfertility often remains unknown. Therefore, we outline the role of nutritional and biochemical factors in reproduction and subfertility. A literature search was performed using MEDLINE, Science Direct and bibliographies of published work with both positive and negative results. The studies showed that folate has a role in spermatogenesis. In female reproduction, folate is also important for oocyte quality and maturation, implantation, placentation, fetal growth and organ development. Zinc has also been implicated in testicular development, sperm maturation and testosterone synthesis. In females, zinc plays a role in sexual development, ovulation and the menstrual cycle. Both folate and zinc have antioxidant properties that counteract reactive oxygen species (ROS). Thiols, such as glutathione, balance the levels of ROS produced by spermatozoa and influence DNA compaction and the stability and motility of spermatozoa. Oocyte maturation, ovulation, luteolysis and follicle atresia are also affected by ROS. After fertilization, glutathione is important for sperm nucleus decondensation and pronucleus formation. Folate, zinc, ROS and thiols affect apoptosis, which is important for sperm release, regulation of follicle atresia, degeneration of the corpus luteum and endometrial shedding. Therefore, the concentrations of these nutrients may have substantial effects on reproduction. In conclusion, nutritional and biochemical factors affect biological processes in male and female reproduction. Further research should identify pathways that may lead to improvements in care and treatment of subfertility.

Genetic variance modifies apoptosis susceptibility in mature oocytes via alterations in DNA repair capacity and mitochondrial ultrastructure

Although the identification of specific genes that regulate apoptosis has been a topic of intense study, little is known of the role that background genetic variance plays in modulating cell death. Using germ cells from inbred mouse strains, we found that apoptosis in mature (metaphase II) oocytes is affected by genetic background through at least two different mechanisms. The first, manifested in AKR/J mice, results in genomic instability. This is reflected by numerous DNA double-strand breaks in freshly isolated oocytes, causing a high apoptosis susceptibility and impaired embryonic development following fertilization. Microinjection of Rad51 reduces DNA damage, suppresses apoptosis and improves embryonic development. The second, manifested in FVB mice, results in dramatic dimorphisms in mitochondrial ultrastructure. This is correlated with cytochrome c release and a high apoptosis susceptibility, the latter of which is suppressed by pyruvate treatment, Smac/DIABLO deficiency, or microinjection of 'normal' mitochondria. Therefore, background genetic variance can profoundly affect apoptosis in female germ cells by disrupting both genomic DNA and mitochondrial integrity.

Fetal and neonatal exposure to nicotine disrupts ovarian function and fertility in adult female rats

Women born to mothers who smoked during pregnancy have been shown to have impaired fertility, although the mechanisms underlying this association are unknown. Nicotine administration in adult animals has adverse effects on the ovary and uterus; however, the effects of fetal exposure to nicotine on postnatal ovarian function have not been determined. The goal of this study was to assess the effect of fetal and neonatal exposure to nicotine on ovarian function and fertility of the offspring. Nulliparous female Wistar rats were given 1 mg.kg-1.d-1 nicotine bitartrate, subcutaneously for 14 d prior to mating, during pregnancy and throughout lactation until weaning. Measures of fertility, breeding success, and serum levels of ovarian steroid hormones in offspring were assessed at 4 and 6 mo of age. Fetal and neonatal exposure to nicotine significantly increased the time to pregnancy as the animals aged. Similarly, evidence of altered ovarian steroidogenesis including increased serum progesterone concentrations and a decreased estrogen:progesterone ratio was observed in 6-mo-old animals. We conclude that fetal and neonatal exposure to nicotine results in delayed ovarian dysfunction in adult female offspring.

C. elegans GLA-3 is a novel component of the MAP kinase MPK-1 signaling pathway required for germ cell survival

During oocyte development in Caenorhabditis elegans, approximately half of all developing germ cells undergo apoptosis. While this process is evolutionarily conserved from worms to humans, the regulators of germ cell death are still largely unknown. In a genetic screen for novel genes involved in germline apoptosis in Caenorhabditis elegans, we identified and cloned gla-3. Loss of gla-3 function results in increased germline apoptosis and reduced brood size due to defective pachytene exit from meiosis I. gla-3 encodes a TIS11-like zinc-finger-containing protein that is expressed in the germline, from the L4 larval stage to adulthood. Biochemical evidence and genetic epistasis analysis revealed that GLA-3 participates in the MAPK signaling cascade and directly interacts with the C. elegans MAPK MPK-1, an essential meiotic regulator. Our results show that GLA-3 is a new component of the MAPK cascade that controls meiotic progression and apoptosis in the C. elegans germline and functions as a negative regulator of the MAPK signaling pathway during vulval development and in muscle cells.

Clinical practice in Turner syndrome

Turner syndrome (TS) is a common genetic disorder, resulting from the partial or complete absence of one sex chromosome, and occurring in approximately 50 per 100,000 liveborn girls. TS is associated with reduced adult height and with gonadal dysgenesis, leading to insufficient circulating levels of female sex steroids and to infertility. Morbidity and mortality are increased in TS but average intellectual performance is within the normal range. A number of recent studies have allowed new insights to be gained with respect to epidemiology, genetics, cardiology, endocrinology and metabolism. Elucidation of the effects of short stature homeobox protein deficiency has explained some of the phenotypic characteristics in TS, principally short stature. Treatment with growth hormone during childhood and adolescence allows a considerable gain in adult height, although the consequences of this treatment in the very long term are not clear. Puberty must be induced in most cases, and female sex hormone replacement therapy (HRT) is given during adult years. The optimal dose of HRT has not been established and, likewise, the benefits and drawbacks of HRT have not been thoroughly evaluated. The risks of type 2 diabetes, type 1 diabetes, hypothyroidism, osteoporosis, congenital heart disease, hypertension, ischemic heart disease, aortic dilatation and dissection, inflammatory bowel disease and celiac disease are clearly elevated, and proper care during adulthood is important. Currently no firm guidelines for diagnosis exist. In conclusion, TS is a condition associated with a number of diseases and conditions that are reviewed in the present paper. Individuals with TS need life-long medical attention.

Naturally suppressed apoptosis prevents follicular atresia and oocyte reserve decline in the adult ovary of Lagostomus maximus (Rodentia, Caviomorpha)

It has been widely accepted that mammalian females are born with a non-renewing, finite pool of oocytes that will be continuously cleared by atresia, with only a small proportion of them reaching ovulation. Apoptosis regulates this mass germ cell death, especially through the balance between pro- and anti-apoptotic proteins encoded by the BCL-2 gene family. The caviomorph rodent Lagostomus maximus, the South American plains viscacha, displays the highest ovulation rate known for a mammal releasing 400–800 eggs per cycle. We tested the hypothesis that in L. maximus massive polyovulation is a consequence of reduced apoptosis resulting in suppressed follicular atresia. We found that anti-apoptotic BCL-2 gene is markedly expressed in all kind of follicles from primordial to fully mature antral stages in the adult ovary of L. maximus. On the other hand, pro-apoptotic BAX gene showed weak signals or was undetectable by immunohistochemical examination. Western blot against both proteins confirmed immunohistochemical results. Screening for DNA fragmentation by TUNEL assay was conspicuously negative in ovaries from both pregnant and non-pregnant females. In addition, α-oestrogen receptor also showed an enhanced expression from primordial stage to fully mature antral follicles. Our results show that natural preferential expression of BCL-2 and restricted BAX expression greatly suppresses apoptosis in the ovary of L. maximus. This prevents the decline of the oocyte reserve by abolishing follicular atresia and enables the highest ovulation rate known for a mammal, 400–800 or more eggs per cycle.

Ovarian follicular growth and atresia: the relationship between cell proliferation and survival

Growth factors and steroids play an important role in the regulation of ovarian follicular development. In cattle, two of the earliest detectable differences between the healthy dominant follicle selected for development to the ovulatory stage and subordinate follicles destined to undergo atresia are the greater availability of IGF and the greater capacity to produce estradiol in the dominant follicle. We have shown that IGF-I and estradiol stimulate the proliferation of bovine granulosa cells in vitro and promote granulosa cell survival by increasing resistance to apoptosis. Furthermore, the ability of IGF-I and estradiol to increase resistance to apoptosis is tied to their ability to promote progression through the cell cycle. Blocking the cell cycle at the transition between the first gap phase and the DNA synthesis phase using a specific inhibitor prevented the protective effects of IGF-I and estradiol against apoptosis. Further experiments showed that the protective effect of IGF-I against apoptosis is mediated by the stimulation of phosphatidylinositol 3-kinase and its downstream target, protein kinase B/Akt. Constitutive activation of Akt by the infection of granulosa cells with a recombinant Akt adenovirus protected against apoptosis, and this effect also depended on cell cycle progression. These experiments show that the protective effect of estradiol and IGF-I against apoptosis depends on unperturbed progression through the cell cycle. Once follicles have developed to the preovulatory stage, the LH surge induces terminal differentiation of granulosa cells and withdrawal from the cell cycle. Bovine granulosa cells withdraw from the cell cycle by 12 h after the LH surge and become resistant to apoptosis, even in the absence of growth factors. Treatment with a progesterone receptor antagonist in vitro caused reentry of granulosa cells into the cell cycle and susceptibility to apoptosis, suggesting that induction of progesterone receptor expression by the LH surge is required for cell cycle withdrawal and resistance to apoptosis. In summary, the susceptibility of granulosa cells to apoptosis depends on the cell cycle. Proliferating granulosa cells in growing follicles depend on growth factors for survival, whereas cells that have terminally differentiated in response to the LH surge are resistant to apoptosis and relatively independent of growth factors for survival.

Investigation of the human stem cell factor KIT ligand gene, KITLG, in women with 46,XX spontaneous premature ovarian failure

OBJECTIVE

To investigate mutations in the human KIT ligand gene (KITLG) gene as a mechanism of 46,XX spontaneous premature ovarian failure. The human KIT ligand gene, known also as human stem cell factor, is the ligand of the c-kit transmembrane tyrosine kinase receptor (KIT). This ligand-receptor interaction is known to play important roles in mouse germ cell migration and proliferation.

DESIGN

Cross-sectional study.

SETTING

Clinical research center.

PATIENT(S)

Forty women with 46,XX spontaneous premature ovarian failure.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Single-stranded conformational polymorphism analysis and DNA sequencing.

RESULT(S)

We found one nucleotide change of the KITLG coding region (811G-->T) that led to an alteration of the amino acid composition of the KITLG protein in one Caucasian patient (Asp210Tyr). However, we found the same alteration in two normal control Caucasian samples. Three nucleotide substitutions were found in the noncoding exon of KITLG (exon 10). We also identified two intronic polymorphisms. Thus, we did not identify a single significant mutation in the coding region of the KITLG gene in any of 40 patients (upper 95% confidence limit is 7.2%).

CONCLUSION(S)

Mutations in the coding regions of the KITLG gene appear not to be a common cause of 46,XX spontaneous premature ovarian failure in North American women.

CXCR4/SDF1 interaction inhibits the primordial to primary follicle transition in the neonatal mouse ovary

The molecular mechanisms behind the entry of the primordial follicle into the growing follicle pool remain poorly understood. To investigate this process further, a microarray-based comparison was undertaken between 2-day postpartum mouse ovaries consisting of primordial follicles/naked oocytes only and those with both primordial follicles and newly activated follicles (7-day postpartum). Gene candidates identified included the chemoattractive cytokine stromal derived factor-1 (SDF1) and its receptor CXCR4. SDF1 and CXCR4 have been implicated in a variety of physiological processes including the migration of embryonic germ cells to the gonads. SDF1-alpha expression increased with the developmental stage of the follicle. Embryonic expression was found to be dichotomous post-germ cell migration, with low expression in the female. Immunohistochemical studies nonetheless indicate that the autocrine pattern of expression ligand and receptor begins during embryonic life. Addition of recombinant SDF1-alpha to neonatal mouse ovaries in vitro resulted in significantly higher follicle densities than for control ovaries. TUNEL analysis indicated no detectable difference in populations of apoptotic cells of treated or control ovaries. Treated ovaries also contained a significantly lower percentage of activated follicles as determined by measurement of oocyte diameter and morphological analysis. Treatment of cultured ovaries with an inhibitor of SDF1-alpha, AMD3100, ablated the effect of SDF1-alpha. By retaining follicles in an unactivated state, SDF1/CXCR4 signaling may play an important role in maintaining the size and longevity of the primordial follicle pool.

Impaired germ cell development due to compromised cell cycle progression in Skp2-deficient mice

BACKGROUND

The gonads are responsible for the production of germ cells through both mitosis and meiosis. Skp2 is the receptor subunit of an SCF-type ubiquitin ligase and is a major regulator of the progression of cells into S phase of the cell cycle, which it promotes by mediating the ubiquitin-dependent degradation of p27, an inhibitor of cell proliferation. However, the role of the Skp2-p27 pathway in germ cell development remains elusive.

RESULTS

We now show that disruption of Skp2 in mice results in a marked impairment in the fertility of males, with the phenotypes resembling Sertoli cell-only syndrome in men. Testes of Skp2-/- mice manifested pronounced germ cell hypoplasia accompanied by massive apoptosis in spermatogenic cells. Flow cytometry revealed an increased prevalence of polyploidy in spermatozoa, suggesting that the aneuploidy of these cells is responsible for the induction of apoptosis. Disruption of the p27 gene of Skp2-/- mice restored germ cell development, indicating that the testicular hypoplasia of Skp2-/- animals is attributable to the antiproliferative effect of p27 accumulation.

CONCLUSION

Our results thus suggest that compromised cell cycle progression caused by the accumulation of p27 results in aneuploidy and the induction of apoptosis in gonadal cells of Skp2-/- mice. The consequent reduction in the number of mature gametes accounts for the decreased fertility of these animals. These findings reinforce the importance of the Skp2-p27 pathway in cell cycle regulation and in germ cell development.

Mitochondria and the success of somatic cell nuclear transfer cloning: from nuclear-mitochondrial interactions to mitochondrial complementation and mitochondrial DNA recombination

The overall success of somatic cell nuclear transfer (SCNT) cloning is rather unsatisfactory, both in terms of efficacy and from an animal health and welfare point of view. Most research activities have concentrated on epigenetic reprogramming problems as one major cause of SCNT failure. The present review addresses the limited success of mammalian SCNT from yet another viewpoint, the mitochondrial perspective. Mitochondria have a broad range of critical functions in cellular energy supply, cell signalling and programmed cell death and, thus, affect embryonic and fetal development, suggesting that inadequate or perturbed mitochondrial functions may adversely affect SCNT success. A survey of perinatal clinical data from human subjects with deficient mitochondrial respiratory chain activity has revealed a plethora of phenotypes that have striking similarities with abnormalities commonly encountered in SCNT fetuses and offspring. We discuss the limited experimental data on nuclear-mitochondrial interaction effects in SCNT and explore the potential effects in the context of new findings about the biology of mitochondria. These include mitochondrial fusion/fission, mitochondrial complementation and mitochondrial DNA recombination, processes that are likely to be affected by and impact on SCNT cloning. Furthermore, we indicate pathways that could link epigenetic reprogramming and mitochondria effects in SCNT and address questions and perspectives for future research.

Clinical potential and putative risks of fertility preservation in children utilizing gonadal tissue or germline stem cells

Rapid progress in the development of novel experimental strategies to generate fertile gametes from cryo-preserved ovarian and testicular tissue motivates oncologists to investigate ways in which gonadal tissue might be preserved. Childhood cancer patients remain the major pediatric group which can benefit from these techniques. Other potential candidates include patients with systemic diseases, which require gonadotoxic chemotherapy, patients undergoing gonadectomy, patients with Turner or Kleinefelter's syndrome, and boys with cryptorchid testes. This review aims to present an overview of the current state of knowledge in experimental germ stem cell transplantation in higher primates including humans, and the clinical risks and limitations related to such procedures in children. This area of research is discussed in the context of the potential future options that may become available for preserving fertility in boys and girls.

Developmental apoptosis in C. elegans: a complex CEDnario

Apoptosis, an evolutionarily conserved programme of cellular self-destruction, is essential for the development and survival of most multicellular animals. It is required to ensure functional organ architecture and to maintain tissue homeostasis. During development of the simple nematode Caenorhabditis elegans, apoptosis claims over 10% of the somatic cells that are generated - these cells were healthy but unnecessary. Exciting insights into the regulation and execution of apoptosis in C. elegans have recently been made. These new findings will undoubtedly influence our perception of developmental apoptosis in more complex species, including humans.

Illuminating the role of caspases during Drosophila oogenesis

Cell death is a prominent feature of animal germline development. In Drosophila, the death of 15 nurse cells is linked to the development of each oocyte. In addition, females respond to poor environmental conditions by inducing egg chamber death prior to yolk uptake by the oocyte. To study these two forms of cell death, we analyzed caspase activity in the germline by expressing a transgene encoding a caspase cleavage site flanked by cyan fluorescent protein and yellow fluorescent protein. When expressed in ovaries undergoing starvation-induced apoptosis, this construct was an accurate reporter of caspase activity. However, dying nurse cells at the end of normal oogenesis showed no evidence of cytoplasmic caspase activity. Furthermore, although expression of the caspase inhibitors p35 or Drosophila inhibitor of apoptosis protein 1 blocked starvation-induced death, it did not affect normal nurse cell death or overall oogenesis in well-fed females. Our data suggest that caspases play no role in developmentally programmed nurse cell death.

Apoptosis in bovine cumulus-oocyte complexes after exposure to polychlorinated biphenyl mixtures during in vitro maturation

Aroclor-1254 (A-1254) is a commercial mixture of coplanar (dioxin-like) and non-coplanar (non dioxin-like) polychlorinated biphenyls (PCBs) affecting bovine oocyte in vitro maturation (IVM) and developmental competence. In the present study, the role of cumulus cell apoptosis in mediating the toxic effects of PCBs during in vitro maturation has been investigated. Results indicate that exposure of cumulus-oocyte complexes (COCs) to A-1254 significantly induced apoptosis of cumulus cells. Furthermore, A-1254 significantly increased the expression of the pro-apoptotic gene, Bax, concomitantly reducing the level of the anti-apoptotic gene, Bcl-2, in the cumulus cell compartment. The effects of pure mixtures of coplanar (PCB 77, 126 and 169) or non-coplanar (PCB 52, 101 and 153) PCBs were examined. Exposure of COCs to coplanar PCBs affected maturation at doses as low as 100.6 pg/ml. Furthermore, a significant increase in apoptosis and in Bax mRNA expression was observed. No variations in maturation or apoptosis were observed in the non-coplanar PCB group. To further analyze the role of cumulus cells, COCs and denuded oocytes (DOs) have been exposed to A-1254 or coplanar PCBs during IVM. Exposure of COCs significantly reduced the percentage of matured oocytes after 24 h of culture in both treatments. In contrast, exposure of DOs significantly decreased the maturation rate only at the highest dose investigated (100-fold greater than that affecting COCs). Taken together, the results indicate a direct role of cumulus cell apoptosis in mediating PCB toxicity on bovine oocytes, and a direct relationship between congener planarity and toxicity in bovine oocytes is suggested.

Programmed cell death in floral organs: how and why do flowers die?

BACKGROUND

Flowers have a species-specific, limited life span with an irreversible programme of senescence, which is largely independent of environmental factors, unlike leaf senescence, which is much more closely linked with external stimuli.

TIMING

Life span of the whole flower is regulated for ecological and energetic reasons, but the death of individual tissues and cells within the flower is co-ordinated at many levels to ensure correct timing. Some floral cells die selectively during organ development, whereas others are retained until the whole organ dies.

TRIGGERS

Pollination is an important floral cell death trigger in many species, and its effects are mediated by the plant growth regulator (PGR) ethylene. In some species ethylene is a major regulator of floral senescence, but in others it plays a very minor role and the co-ordinating signals involved remain elusive. Other PGRs such as cytokinin and brassinosteroids are also important but their role is understood only in some specific systems.

MECHANISMS

In two floral cell types (the tapetum and the pollen-tube) there is strong evidence for apoptotic-type cell death, similar to that in animal cells. However, in petals there is stronger evidence for an autophagous type of cell death involving endoplasmic reticulum-derived vesicles and the vacuole. Proteases are important, and homologues to animal caspases, key regulators of animal cell death, exist in plants. However, their role is not yet clear.

COMPARISON WITH OTHER ORGANS

There are similarities to cell death in other plant organs, and many of the same genes are up-regulated in both leaf and petal senescence; however, there are also important differences for example in the role of PGRs.

CONCLUSIONS

Understanding gene regulation may help to understand cell death in floral organs better, but alone it cannot provide all the answers.

Follicular atresia during Dacus oleae oogenesis

Programmed cell death, constitutes a common fundamental incident that occurs during oogenesis in a variety of different animals. It plays a significant role in the maturation process of the female gamete and also in the removal of abnormal and superfluous cells at certain checkpoints of development. In the present study, we demonstrate the existence of follicular atresia during mid-oogenesis in the olive fruit fly Dacus oleae (Tephritidae). The number of atretic follicles increases following the age of the fly, suggesting for the presence of an age-susceptible process. The atretic follicles contain nurse cells that exhibit chromatin condensation, DNA fragmentation and actin cytoskeleton alterations, as revealed by propidium iodide staining, TUNEL labeling and phalloidin-FITC staining. Conventional light and electron microscopy disclose that the nurse cell remnants are phagocytosed by the adjacent follicle cells. The follicular epithelium also eliminates the oocyte through phagocytosis, resulting to an egg chamber with no compartmentalized organization. The data presented herein are very similar compared to previous reported results in other Diptera species, strongly suggesting the occurrence of a phylogenetically conserved mechanism of follicular atresia. All these observations also support the notion that mid-oogenesis in D. oleae may be the critical regulation point at which superfluous and defective egg chambers are selectively eliminated before they reach maturity.

Molecular requirements for doxorubicin-mediated death in murine oocytes

We previously published evidence that oocytes exposed to doxorubicin (DXR), a widely used chemotherapeutic agent, rapidly undergo morphological and biochemical changes via discrete effector signaling pathways consistent with the occurrence of apoptosis. In this report, we elucidated the molecular requirements for actions of this drug in oocytes. Our results indicate that within 1 h of exposure DXR causes rapid DNA damage, and commits the oocyte to cytoplasmic fragmentation by the fourth hour, followed by delayed oocyte activation and execution of cytoplasmic fragmentation. Inhibitors that interfere with oocyte activation consistently rescue cytoplasmic fragmentation, but fail to suppress DNA damage. There was evidence of depletion of Bax, Caspase-2, MA-3 and Bcl-x transcripts, suggesting that modulations by DXR caused recruitment of these maternal transcripts into the translation process. Furthermore, sphingolipids such as sphingosine-1-phosphate and ceramide modulate DXR actions by, respectively, altering its intracellular trafficking, or by sustaining the drug's contact with DNA.

Altered patterns of meiotic recombination in human fetal oocytes with asynapsis and/or synaptonemal complex fragmentation at pachytene

Meiotic recombination was analysed in human fetal oocytes to determine whether recombination errors are associated with abnormal chromosome synapsis. Immunostaining was used to identify the synaptonemal complex (SC, the meiosis-specific proteinaceous structure that binds homologous chromosomes) and the DNA mismatch repair protein, MLH1, that locates recombination foci. It was found that 57.1-74.2% of zygotene oocytes showed fragmentation and/or defective chromosome synapsis. Fewer such abnormal cells occurred at pachytene (15.8-28.9%). MLH1 foci were present from zygotene to diplotene in both normal and abnormal oocytes. However, the proportions of oocytes having MLH1 foci, and mean numbers of foci per oocyte, were both lower in abnormal oocytes. Oocytes with fragmented SC had more foci than those with synaptic anomalies. Analysis of chromosomes 13, 18, 21 and X by fluorescence in-situ hybridization (FISH) did not implicate particular chromosomes in recombination deficiency. These observations indicate that recombination is disturbed in oocytes with SC fragmentation and/or synaptic abnormalities during meiotic prophase I. Such disturbances might be a risk factor for selection of fetal oocytes for atresia, as occurs for homologous chromosome pairing. Recombination errors may potentially increase the risk of abnormal chromosome segregation in oocytes that survive and contribute to the reserve in the mature ovary.

Metabolic regulation of oocyte cell death through the CaMKII-mediated phosphorylation of caspase-2

Vertebrate female reproduction is limited by the oocyte stockpiles acquired during embryonic development. These are gradually depleted over the organism's lifetime through the process of apoptosis. The timer that triggers this cell death is yet to be identified. We used the Xenopus egg/oocyte system to examine the hypothesis that nutrient stores can regulate oocyte viability. We show that pentose-phosphate-pathway generation of NADPH is critical for oocyte survival and that the target of this regulation is caspase-2, previously shown to be required for oocyte death in mice. Pentose-phosphate-pathway-mediated inhibition of cell death was due to the inhibitory phosphorylation of caspase-2 by calcium/calmodulin-dependent protein kinase II (CaMKII). These data suggest that exhaustion of oocyte nutrients, resulting in an inability to generate NADPH, may contribute to ooctye apoptosis. These data also provide unexpected links between oocyte metabolism, CaMKII, and caspase-2.

Oocyte generation in adult mammalian ovaries by putative germ cells in bone marrow and peripheral blood

It has been suggested that germline stem cells maintain oogenesis in postnatal mouse ovaries. Here we show that adult mouse ovaries rapidly generate hundreds of oocytes, despite a small premeiotic germ cell pool. In considering the possibility of an extragonadal source of germ cells, we show expression of germline markers in bone marrow (BM). Further, BM transplantation restores oocyte production in wild-type mice sterilized by chemotherapy, as well as in ataxia telangiectasia-mutated gene-deficient mice, which are otherwise incapable of making oocytes. Donor-derived oocytes are also observed in female mice following peripheral blood transplantation. Although the fertilizability and developmental competency of the BM and peripheral blood-derived oocytes remain to be established, their morphology, enclosure within follicles, and expression of germ-cell- and oocyte-specific markers collectively support that these cells are bona fide oocytes. These results identify BM as a potential source of germ cells that could sustain oocyte production in adulthood.

Apoptose ovocytaire

Apoptosis has been reported in oocyte and preimplantation embryo. The developmental potential of embryo could be related to its rate of apoptosis. This apoptotic fate could be modulated by suboptimal culture conditions: however, a critical role is played by gamete quality and in particular, oocyte apoptosis. Thus, the investigation of apoptosis-related genes and mechanisms in oocyte is crucial. New technologies, such as microarrays, may contribute to the elucidation of molecular pathways involved in oocyte survival and maturation. Besides in vitro culture and ART, the study of oocyte apoptosis could benefit to research in the fields of menopause or cancer treatment.

On the number of founding germ cells in humans

Background

The number of founding germ cells (FGCs) in mammals is of fundamental significance to the fidelity of gene transmission between generations, but estimates from various methods vary widely. In this paper we obtain a new estimate for the value in humans by using a mathematical model of germ cell development that depends on available oocyte counts for adult women.

Results

The germline-development model derives from the assumption that oogonial proliferation in the embryonic stage starts with a founding cells at t = 0 and that the subsequent proliferation can be defined as a simple stochastic birth process. It follows that the population size X(t) at the end of germline expansion (around the 5^th month of pregnancy in humans; t = 0.42 years) is a random variable with a negative binomial distribution. A formula based on the expectation and variance of this random variable yields a moment-based estimate of a that is insensitive to the progressive reduction in oocyte numbers due to their utilization and apoptosis at later stages of life. In addition, we describe an algorithm for computing the maximum likelihood estimation of the FGC population size (a), as well as the rates of oogonial division and loss to apoptosis. Utilizing both of these approaches to evaluate available oocyte-counting data, we have obtained an estimate of a = 2 – 3 for Homo sapiens.

Conclusion

The estimated number of founding germ cells in humans corresponds well with values previously derived from chimerical or mosaic mouse data. These findings suggest that the large variation in oocyte numbers between individual women is consistent with a smaller founding germ cell population size than has been estimated by cytological analyses.

From oogenesis through gastrulation: developmental regulation of apoptosis

Apoptosis is a mechanism employed by multicellular organisms throughout development as a means of eliminating damaged or otherwise unwanted cells. From oogenesis through fertilization and gastrulation, organisms use an array of cell- and tissue-specific mechanisms to regulate the apoptotic program in response to stress or developmental cues. Since cell death regulation is tightly interwoven with cell cycle and checkpoint controls, and embryos of the fly, fish and frog exhibit unique embryonic cell cycle regulation, it is of great interest to understand how early embryos coordinate these cellular functions.

A delay in age at first mating results in the loss of future reproductive potential via apoptosis

Women who delay childbearing risk subfertility. However, this loss of fertility is not a simple function of aging. Women who have had children early in life tend to maintain fertility longer, measured as a later age at menopause. But why should otherwise healthy women lose reproductive capacity? Loss of fertility independent of senescence, menopause, has been approached from two perspectives: evolution and development. Evolutionary biologists focus on how natural selection favors survival after reproductive ability has ceased, whereas reproductive biologists examine mechanisms by which women lose fertility with age and factors that influence the rate of reproductive aging. Combining mechanistic studies with evolutionary theory should allow us to define principles of the evolution of postembryonic development of ovaries, including the role of reproductive timing relative to sexual maturation. Achieving this will require identifying appropriate, and more experimentally tractable, taxa in which to study how early reproductive events influence lifetime fertility. We work with an invertebrate species, the cockroach Nauphoeta cinerea, with a complex reproductive biology in which females experience reproductive cycles, give live birth, and show age-related decline in fertility. Thus, N. cinerea provides an opportunity to use an experimental approach to examine mechanisms by which females lose reproductive potential as they delay reproduction. Our results demonstrate that the loss of both oocytes ready for fertilization and future oocytes in females that delay mating is because of apoptosis. We suggest that loss of fertility because of delayed mating may originate in a nonadaptive response in control of apoptosis through mistiming of reproduction.

Apoptosis-inhibiting activities of BIR family proteins in Xenopus egg extracts

In many animal species including Xenopus, ovulated eggs possess an intrinsic apoptotic execution system. This program is inhibited for a limited time by some maternal apoptosis inhibitors, although their molecular properties remain uncharacterized. Baculovirus IAP repeat (BIR) family proteins contain evolutionarily conserved BIR domains and play important roles in apoptosis suppression, and are therefore good candidates as maternal apoptosis inhibitors. We identified four maternal BIR family proteins in Xenopus eggs and, using the biochemical advantages of egg extracts, examined their physiological functions. These molecules included two survivin-related proteins, xEIAP/XLX, and a possible ortholog of XIAP named xXIAP. The addition of recombinant xXIAP greatly delayed apoptotic execution, whereas the immunodepletion of endogenous xXIAP significantly accelerated the onset of apoptosis. In contrast, xEIAP/XLX was a poor apoptosis inhibitor, and neither of the survivin orthologs showed anti-apoptotic activity in our assay. Both xEIAP/XLX and xXIAP were degraded by activated caspases, and also by a novel proteolytic system that required the presence of C-terminal RING finger domain but was insensitive to proteasome inhibition. Our data suggest that the regulation of endogenous xXIAP concentration is important for the survival of Xenopus eggs.

Programmed cell death in the germline

In many organisms, programmed cell death of germ cells is required for normal development. This often occurs through highly conserved events including the transfer of vital cellular material to the growing gametes following death of neighboring cells. Germline cell death also plays a role in such diverse processes as removal of abnormal or superfluous cells at certain checkpoints, establishment of caste differentiation, and individualization of gametes. This review focuses on the cell death events that occur during gametogenesis in both vertebrates and invertebrates. It also examines the signals and machinery that initiate and carry out these germ cell deaths.

Apoptosis in the ovary: molecular mechanisms

Cell death was first described in rabbit ovaries (Graaffian follicles), the phenomenon being called 'chromatolysis' rather than apoptosis. In humans, the ovarian endowment of primordial follicles is established during fetal life. Apoptotic cell death depletes this endowment by at least two-thirds before birth, executed with the help of several players and pathways conserved from worms to humans. To date, apoptosis has been reported to be involved in oogenesis, folliculogenesis, oocyte loss/selection and atresia. Several pro-survival and pro-apoptotic molecules are involved in ovarian apoptosis with the delicate balance between them being the determinant for the final destiny of the follicular cells. This review critically analyses the current knowledge about the biological roles of these molecules and their relevance to the dynamics of follicle development. It also presents the existing literature and assesses the gaps in our knowledge.

A central role for ceramide in the age‐related acceleration of apoptosis in the female germline

An age-dependent acceleration of apoptosis occurs in female germ cells (oocytes), and this requires communication between the oocyte and its surrounding somatic (cumulus) cells. Here we show in aged mice that ceramide is translocated from cumulus cells into the adjacent oocyte and induces germ cell apoptosis that can be prevented by sphingosine-1-phosphate. Trafficking of ceramide requires gap junction-dependent communication between the cumulus cells and the oocyte as well as intact lipid rafts. Further, the occurrence of the elevated incidence of apoptosis in oocytes of aged females is concomitant with an enhanced sensitivity of the oocyte to a spike in cytosolic ceramide levels, as well as increased bax mRNA and Bax protein levels. Thus, the force driving the age-related increase in female germ cell death is multifactorial, but changes in the intercellular trafficking of ceramide, along with hypersensitivity of oocytes to ceramide, are key factors in this process.

Extreme heterogeneity in the molecular events leading to the establishment of chiasmata during meiosis i in human oocytes

In humans, ~50% of conceptuses are chromosomally aneuploid as a consequence of errors in meiosis, and most of these aneuploid conceptuses result in spontaneous miscarriage. Of these aneuploidy events, 70% originate during maternal meiosis, with the majority proposed to arise as a direct result of defective crossing over during meiotic recombination in prophase I. By contrast, <1%-2% of mouse germ cells exhibit prophase I-related nondisjunction events. This disparity among mammalian species is surprising, given the conservation of genes and events that regulate meiotic progression. To understand the mechanisms that might be responsible for the high error rates seen in human females, we sought to further elucidate the regulation of meiotic prophase I at the molecular cytogenetic level. Given that these events occur during embryonic development in females, samples were obtained during a defined period of gestation (17-24 weeks). Here, we demonstrate that human oocytes enter meiotic prophase I and progress through early recombination events in a similar temporal framework to mice. However, at pachynema, when chromosomes are fully paired, we find significant heterogeneity in the localization of the MutL homologs, MLH1 and MLH3, among human oocyte populations. MLH1 and MLH3 have been shown to mark late-meiotic nodules that correlate well with--and are thought to give rise to--the sites of reciprocal recombination between homologous chromosomes, which suggests a possible 10-fold variation in the processing of nascent recombination events. If such variability persists through development and into adulthood, these data would suggest that as many as 30% of human oocytes are predisposed to aneuploidy as a result of prophase I defects in MutL homolog-related events.

Establishment of oocyte population in the fetal ovary: primordial germ cell proliferation and oocyte programmed cell death

Strict control of cell proliferation and cell loss is essential for the coordinated functions of different cell populations in complex multicellular organisms. Oogenesis is characterized by a first phase occurring during embryo-fetal life and in common with spermatogenesis, during which mitotic proliferation of the germline stem cells, the primordial germ cells (PGC), prevails over germ cell death. The result is the formation of a relatively high number of germ cells depending on the species, ready to enter sex specific differentiation. In the female, PGC enter into meiosis and become oocytes, thereby ending their stem cell potential. After entering into meiosis in the fetal ovary, oocytes pass through leptotene, zygotene and pachytene stages before arresting in the last stage of meiotic prophase I, the diplotene or dictyate stage at about the time of birth. The most part of oocytes die during the fetal period or shortly after birth. It is widely accepted that in mammals a female is born with a fixed number of oocytes within the ovaries, which over the years progressively decreases without possibility for renewal. Once the oocyte reserve has been exhausted, ovarian senescence, driving what is referred to as the menopause in women, rapidly ensues. The fertile lifespan of a female depends by the size of the oocyte pool at birth and the rapidity of the oocyte pool depletion. Which mechanisms control PGC proliferation? Why do most of the oocytes die during fetal life and what are the mechanisms of such massive degeneration? Is it possible to prolong the lifespan of a female by reducing oocyte lost during the fetal life? This review reports some of the most recent results obtained in an attempt to answer these questions.

Deadly decisions: the role of genes regulating programmed cell death in human preimplantation embryo development

Human preimplantation embryo development is prone to high rates of early embryo wastage, particularly under current in vitro culture conditions. There are many possible underlying causes for embryo demise, including DNA damage, poor embryo metabolism and the effect of suboptimal culture media, all of which could result in an imbalance in gene expression and the failed execution of basic embryonic decisions. In view of the complex interactions involved in embryo development, a thorough understanding of these parameters is essential to improving embryo quality. An increasing body of evidence indicates that cell fate (i.e. survival/differentiation or death) is determined by the outcome of specific intracellular interactions between pro- and anti-apoptotic proteins, many of which are expressed during oocyte and preimplantation embryo development. The recent availability of mutant mice lacking expression of various genes involved in the regulation of cell survival has enabled rapid progress towards identifying those molecules that are functionally important for normal oocyte and preimplantation embryo development. In this review we will discuss the current understanding of the regulation of cell death gene expression during preimplantation embryo development, with a focus on human embryology and a discussion of animal models where appropriate.

Involvement of Apoptosis in Disruption of Developmental Competence of Bovine Oocytes by Heat Shock During Maturation1

Various pathological stimuli such as radiation, environmental toxicants, oxidative stress, and heat shock can initiate apoptosis in mammalian oocytes. Experiments were performed to examine whether apoptosis mediated by group II caspases is the cause for disruption of oocyte function by heat shock applied during maturation in cattle. Bovine cumulus-oocyte complexes (COCs) were cultured at 38.5, 40, or 41 degrees C for the first 12 h of maturation. Incubation during the last 10 h of maturation, fertilization, and embryonic development were at 38.5 degrees C and 5% (v/v) CO2 for all treatments. In the first experiment, exposure of COCs to thermal stress during the first 12 h of maturation reduced cleavage rate and the number of oocytes developing to the blastocyst stage. In the second experiment, a higher percentage of TUNEL-positive oocytes was noted at the end of maturation for oocytes matured at 40 and 41 degrees C than for those at 38.5 degrees C. In addition, the distribution of oocytes classified as having high (>25 intensity units), medium (15-25 intensity units), and low (<15 intensity units) caspase activity was affected by treatment, with a greater proportion of heat-shocked oocytes having medium or high activity. In the third experiment, COCs were placed in maturation medium with vehicle (0.5% [v/v] DMSO) or 200 nM z-DEVD-fmk, an inhibitor of group II caspases. The COCs were matured at 38.5 or 41 degrees C, fertilized and cultured for 8 days. The inhibitor blocked the effect of heat shock on cleavage rate and the percentage of oocytes and cleaved embryos developing to the blastocyst stage. In conclusion, heat shock during oocyte maturation can promote an apoptotic response mediated by group II caspases, which, in turn, leads to disruption of the oocyte's capacity to support early embryonic development following fertilization.

Eggs over easy: cell death in the Drosophila ovary

Programmed cell death is the most common fate of female germ cells in Drosophila and many animals. In Drosophila, oocytes form in individual egg chambers that are supported by germline nurse cells and surrounded by somatic follicle cells. As oogenesis proceeds, 15 nurse cells die for every oocyte that is produced. In addition to this developmentally regulated cell death, groups of germ cells or entire egg chambers may be induced to undergo apoptosis in response to starvation or other insults. Recent findings suggest that these different types of cell death involve distinct genetic pathways. This review focuses on progress towards elucidating the molecular mechanisms acting during programmed cell death in Drosophila oogenesis.

Follicular epithelial cell apoptosis of atretic follicles within developing ovaries of the mosquito Culex pipiens pallens

Follicular atresia, the degeneration of developing follicles, is always incident to normal oogenesis in both oviparous and viviparous animals. Photo- and electron-microscopic observation of degenerating follicles within developing ovaries taken from blood-fed Culex pipiens pallens mosquitoes showed gradual degradation of the internal structures including yolk granules in the oocyte. The epithelial cells, which sometimes incorporated yolk granules from the oocyte along with the shrinkage of the follicle, gradually lost their uniform columnar shape, while their integrity as a covering layer remained. In situ active caspase analysis detected active enzymes in these epithelial regions. In the latest stages of atresia where either the nurse cells or oocyte were lost, the follicle was mainly comprised of irregularly shaped epithelial cells, and some of these cells' nuclei contained condensed chromatin peripherally, one of the characteristics of apoptotic cells. Also terminaldeoxynucleotidyl transferase-mediated dUTP-biotin nick-end labeling treatment indicated that DNA fragmentation occurred in these follicles. It seems likely that in atretic follicles the epithelial cells survive to play key roles in the event, and then finally undergo their own apoptotic cell death so as to give the developmental site to the next follicle in the same ovariole.

Successful spontaneous pregnancies in women older than 45 years

OBJECTIVE

To characterize the reproductive history of women who delivered an infant after a spontaneous pregnancy after the age of 45 years.

DESIGN

Observational study.

SETTING

University departments.

PATIENT(S)

Two hundred nine women who conceived spontaneously and had their most recent delivery after the age of 45 years.

INTERVENTION(S)

Review of all individual medical charts for a complete history of all pregnancies.

MAIN OUTCOME MEASURE(S)

Gravidity, parity, and spontaneous abortion (SAB) rate.

RESULT(S)

The mean (+/-SD) age at last delivery was 45.7 +/- 0.9 years (range: 45-49). The mean parity was 9.6 +/- 4 children (range: 2-20): 81% of the women were grandmultiparas (> or =6 deliveries) and 46% were grand-grandmultiparas (> or =11 deliveries). The mean number of SAB was 1.9 +/- 1.9 (range: 0-9). Increased parity did not have a protective effect on abortion rate: 12.9% for parity 2-5, 15.6% for parity 6-10, and 21.3% for parity 11-20. Women in the study group differed significantly in their SAB rate from a general population: 11.3% vs. 17.7% at age 39, 13.2% vs. 33.8% at age 44, and 9.1% vs. 33.8% at age 45.

CONCLUSION(S)

Women who conceived at or after 45 years of age were mostly grandmultiparas. Although multiparity in itself did not affect SAB rates, this measure was remarkably low in our exceptionally fertile group as compared with the rates published for a general population. This unique group of grandmultiparous women might possess a genetic propensity that delays the normal rate of ovarian and oocyte senescence.

Germline stem cells and follicular renewal in the postnatal mammalian ovary

A basic doctrine of reproductive biology is that most mammalian females lose the capacity for germ-cell renewal during fetal life, such that a fixed reserve of germ cells (oocytes) enclosed within follicles is endowed at birth. Here we show that juvenile and adult mouse ovaries possess mitotically active germ cells that, based on rates of oocyte degeneration (atresia) and clearance, are needed to continuously replenish the follicle pool. Consistent with this, treatment of prepubertal female mice with the mitotic germ-cell toxicant busulphan eliminates the primordial follicle reserve by early adulthood without inducing atresia. Furthermore, we demonstrate cells expressing the meiotic entry marker synaptonemal complex protein 3 in juvenile and adult mouse ovaries. Wild-type ovaries grafted into transgenic female mice with ubiquitous expression of green fluorescent protein (GFP) become infiltrated with GFP-positive germ cells that form follicles. Collectively, these data establish the existence of proliferative germ cells that sustain oocyte and follicle production in the postnatal mammalian ovary.

Current concepts in Bcl-2 family member regulation of female germ cell development and survival

Since the cloning of the bcl-2 gene in 1985, considerable progress has been made in elucidating the function of Bcl-2 and related proteins in controlling apoptosis. Although much of this work initially relied on the ectopic expression of bcl-2 gene family members in cell lines in vitro, a number of genetically manipulated mice have been generated to better understand the in vivo significance of specific family members to organ development and homeostasis. Of the many tissues that exhibit apoptosis at some point during fetal or postnatal life, the female gonads arguably possess one of the highest and most protracted incidences of apoptosis, associated with development and maturation of the germ line. Moreover, female germ cells (oocytes) are, for as-yet poorly understood reasons, extremely vulnerable to a host of pathological insults, such as anti-cancer therapies, that ultimately cause premature ovarian failure and infertility due to accelerated oocyte death. Accordingly, efforts to understand the occurrence and regulation of apoptosis in the ovary are of considerable importance from both biological and clinical perspectives. This review will highlight what is known of apoptosis in the female gonads, and the role that Bcl-2 family members play in regulating this process.

Identification of genes involved in apoptosis and dominant follicle development during follicular waves in cattle

We hypothesize that granulosa and theca cells from growing dominant follicles, with relatively high intrafollicular concentrations of estradiol, have a greater expression of genes involved in inhibiting apoptosis pathways and lower expression of genes involved in apoptosis pathways than growing subordinate follicles with lower estradiol concentrations. Using the well-characterized bovine dominant follicle model, we collected granulosa and theca cells from individual dominant and the largest subordinate follicle 3 days after initiation of a follicular wave in four animals. Based on ultrasound analysis, both follicle types were in the growth phase at the time of ovariectomy. However, dominant follicles were larger (9.8 +/- 1.0 versus 7.6 +/- 0.6 mm in diameter, P < 0.05) and had greater intrafollicular concentrations of estradiol (132.2 +/-3 8.5 versus 24.1 +/- 12.1 ng/ml, P < 0.05), compared with the largest subordinate follicles. We used bovine cDNA microarrays, which contained a total of 1400 genes, including a subset of 53 genes known to be involved in apoptosis pathways, to determine which apoptosis and marker genes from each of the four dominant versus subordinate follicles were potentially differentially expressed. Using a low stringency-screening criterion, 22 genes were identified. Quantitative real-time polymerase chain reaction confirmed that 16 of these genes were differentially expressed. Our novel results demonstrate that the high intrafollicular concentrations of estradiol in growing dominant follicles were positively associated with enhanced expression of mRNAs in granulosa cells for aromatase, LH receptor, estradiol receptor beta, DICE-1, and MCL-1, compared with granulosa cells from subordinate follicles (all survival-associated genes). In contrast, the relatively low intrafollicular concentrations of estradiol in growing subordinate follicles were positively associated with enhanced expression of mRNAs in granulosa cells for beta glycan, cyclo-oxygenase-1, tumor necrosis factor alpha, caspase-activated DNase, and DRAK-2, and in theca cells for beta glycan, caspase 13, P58(IPK), Apaf-1, BTG-3, and TS-BCLL, compared with granulosa or theca cells from dominant follicles (genes that are all associated with cell death and/or apoptosis). We suggest that that these genes may be candidate estradiol target genes and that they may be early markers for the final stages of follicle differentiation or initiation of apoptosis and thus selection of dominant follicles during follicular waves.

MAP kinases regulate unfertilized egg apoptosis and fertilization suppresses death via Ca2+signaling

The default fate for eggs from many species is death by apoptosis and thus, successful fertilization depends upon suppression of the maternal death program. Little is known about the molecular triggers which activate this process or how the fertilization signal suppresses the default maternal apoptotic pathway. The MAP kinase (MAPK) family member, ERK, plays a universal and critical role in several stages of oocyte meiotic maturation, and fertilization results in ERK inactivation. In somatic cells, ERK and other MAPK family members, p38 and JNK, provide opposing signals to regulate apoptosis, however, it is not known whether MAPKs play a regulatory role in egg apoptosis, nor whether suppression of apoptosis by fertilization is mediated by MAPK activity. Here we demonstrate that MAPKs are involved in starfish egg apoptosis and we investigate the relationship between the fertilization induced signaling pathway and MAPK activation. ERK is active in post-meiotic eggs just until apoptosis onset and then p38, JNK and a third kinase are activated, and remain active through execution. Sequential activation of ERK and p38 is necessary for apoptosis, and newly synthesized proteins are required both upstream of ERK and downstream of p38 for activation of the full apoptotic program. Fertilization causes a dramatic rise in intracellular Ca2+, and we report that Ca2+ provides a necessary and sufficient pro-survival signal. The Ca2+ pathway following fertilization of both young and aged eggs causes ERK to be rapidly inactivated, but fertilization cannot rescue aged eggs from death, indicating that ERK inactivation is not sufficient to suppress apoptosis.

Onset and progress of meiotic prophase in the oocytes in the B6.YTIR sex-reversed mouse ovary

When the Y chromosome of a Mus musculus domesticus male mouse (caught in Tirano, Italy) is placed on a C57BL/6J genetic background, approximately half of the XY (B6.YTIR) progeny develop into normal-appearing but infertile females. We have previously reported that the primary cause of infertility can be attributed to their oocytes. To identify the primary defect in the XY oocyte, we examined the onset and progress of meiotic prophase in the B6.YTIR fetal ovary. Using bromo-deoxyuridine incorporation and culture, we determined that the germ cells began to enter meiosis at the developmental ages and in numbers comparable to those in the control XX ovary. Furthermore, the meiotic prophase appeared to progress normally until the late zygotene stage. However, the oocytes that entered meiosis early in the XY ovary failed to complete the meiotic prophase. On the other hand, a considerable number of oocytes entered meiosis at late developmental stages and completed the meiotic prophase in the XY ovary. We propose that the timing of entry into meiosis and the XY chromosomal composition influence the survival of oocytes during meiotic prophase in the fetal ovary.

Intracellular mechanisms regulating cell survival in ovarian follicles

The vertebrate ovary represents a uniquely dynamic organ system charged with the responsibility to initially provide, and subsequently foster, optimal numbers of maturing, viable gametes that will insure the propagation of the species. Seemingly in spite of this charge, >99% of germ cells within the ovaries of mammalian and avian species present at the time of birth or hatch are lost via atresia at some point during the lifespan of the female. The consequence of this ongoing germ cell and ovarian follicle attrition in some species eventually leads to the natural termination of reproductive function (e.g. menopause in humans), while in all species an excessive loss of germ cells frequently results in diminished reproductive potential due to subclinical or clinical infertility. Apoptosis represents the primary pathway by which defective or excessive numbers of follicles are rapidly and effectively eliminated, and this process is actively opposed or entirely suppressed by a variety of cell survival signaling pathways and cellular anti-apoptotic proteins expressed within follicles destined for ovulation. Significantly, such survival mechanisms are regulated by many of the same endocrine-paracrine-autocrine factors that control follicle differentiation. This review will begin by briefly discussing the process of apoptosis, then focus on the varied and often redundant mechanisms that prevent apoptotic cell death in granulosa cells specifically during the late preantral (comparable to the prehierarchal stage of follicle development in avian species) and preovulatory stages of follicle development.

Apoptosis in male germ cells in response to cyclin A1-deficiency and cell cycle arrest

Male mice homozygous for a mutated allele of the cyclin A1 gene (Ccna1) are sterile due to a block in cell cycle progression before the first meiotic division. Meiosis arrest in Ccna1(-/-) spermatocytes is associated with desynapsis abnormalities, lowered MPF activity, and apoptosis as evidenced by TUNEL-positive staining. With time, adult testicular tubules exhibit severe degeneration: some tubules in the older animals are almost devoid of germ cells at various stages of spermatogenesis. The mechanisms by which the cells sense the cell cycle arrest and the regulation of the decision to undergo cell death are under investigation.

Dynamics of ovarian development in the FORKO immature mouse: structural and functional implications for ovarian reserve

Adult Follitropin Receptor Knockout (FORKO) female mice are infertile and estrogen deficient. In order to understand the peri/postnatal developmental changes, we have now characterized the structural and molecular aberrations by comparing several markers of follicular development in 2-, 10-, and 24-day-old wild-type and FORKO females. By Day 24, FORKO mice have 40%-50% smaller uteri and vaginas. Estradiol is undetectable but testosterone and LH levels are already elevated at this age. FORKO ovaries are 45% smaller, indicating a postnatal or perinatal deficit consequent to FSH receptor ablation. This is attributable to decreased numbers of growing follicles and reduced diameter. Developmental markers, such as Müllerian inhibiting substance, GATA-4, estrogen receptor beta, and androgen receptor, were differentially expressed in granulosa cells. In the 2-day-old mutant neonates, a faster recruitment process was noted that later slowed down, impeding development of follicles. This is noteworthy in light of the controversy regarding the direct role of FSH/receptor system as a determinant of small and preantral follicle development in rodents. As the pool of nongrowing primordial follicles specifies the duration of female fertility and timing of reproductive senescence, we believe that the postnatal FORKO female mouse could help in exploring the signals that impact on early folliculogenesis. In addition, our data suggest that the FSH/receptor system is a major contributor to the formation and recruitment of the nongrowing pool of follicles as early as Postnatal Day 2 in the mouse.

Morphodynamics of the follicular-luteal complex during early ovarian development and reproductive life

Female reproductive activity depends upon cyclic morphofunctional changes of the ovarian tissue during the female's fertile period, but the primum movens of an active gonadal rearrangement can be found from early phases of embryo development. To offer a basic account of the main steps of ovarian dynamics, we review the morphofunctional behavior of the follicular-luteal complex in an integrated study using light microscopy and transmission and scanning electron microscopy as well as through the use of numerous drawings. Particular emphasis is given to some reproductive aspects including (1) germ-somatic cell relationships and onset of folliculogenesis during early gonadal development; (2) follicular development and oocyte-follicle cell associations through adult folliculogenesis, finally leading to ovulation; (3) morphodynamics of corpus luteum formation, development, and regression, and (4) degenerative processes involving germ and somatic cells. The results reported, many of which originated in our laboratory, arise from some experiments on laboratory mammals but mostly from a large selection of human specimens. The data obtained are integrated and correlated with classic reports as well as with current views. Crucial biochemical, histophysiological, and clinical aspects are also emphasized.

Mechanisms of follicular dysfunction in 46,XX spontaneous premature ovarian failure

Approximately one half of young women who have 46,XX spontaneous premature ovarian failure have ovarian follicles remaining in the ovary. These follicles function intermittently and unpredictably, and pregnancies can occur in these women without intervention, even many years after the diagnosis. Clearly, the term "premature menopause" is an inaccurate term for this condition. At present, there are no proven therapies that will improve follicular function for these women. Inappropriate luteinization related to low follicle number seems to be a major mechanism of follicular dysfunction. Autoimmune oophoritis, although apparently an uncommon cause of follicular dysfunction in these women, nonetheless presents the opportunity to develop an effective therapy to restore fertility. Young women with 46,XX spontaneous premature ovarian failure benefit from the care of a sensitive clinician, one who is willing to spend a little more time informing them about the diagnosis and referring them to other sources of information. With appropriate medical management and emotional support provided by a sensitive clinician, most young women with 46,XX spontaneous premature ovarian failure will lead happy, healthy, and fulfilling lives.