In silico investigation of the role of miRNAs in a possible developmental origin of prostate cancer in F1 and F2 offspring of mothers exposed to a phthalate mixture.

A previous study using miRNA sequencing revealed that exposure to a mixture of phthalates during pregnancy and lactation dysregulated rno-miR-184 and rno-miR-141-3p in the ventral prostate (VP) of offspring. Here, rno-miR-184 and rno-miR-141-3 expressions were obtained by RT-qPCR in the VP of F1 males as well as in F2 offspring, aiming to establish a relationship with possible oncogenic targets through in silico analyses with multigenerational approach. Additionally, some targets were measured by western blots to highlight a possible relationship between the deregulated miRNAs and some of their targets. VP samples from rats exposed to a mixture of phthalates maternally during pregnancy and lactation (GD10 to PND21-F1) and VP from offspring (F2) were examined. The phthalate mixture at both concentrations (20 µg and 200 mg/kg/day) increased the expression of both miRNAs in the F1 (PND22 and 120) and F2 (descendants of F1-treated males) prostate. Target prediction analysis revealed that both microRNAs are responsible for modulating the expression and synthesis of 40 common targets. A phthalate target association analysis and the HPA database showed an interesting relationship among these possible miRNAs modulated targets with prostate adenocarcinoma and other oncogenic processes. Western blots showed alteration in P63, P53, WNT5, and STAT3 expression, which are targeted by the miRNAs, in the VP of F1/F2 males. The data draw attention to the epigenetic modulation in the prostate of descendants exposed to phthalates and adds to one of the few currently found in the literature to point to microRNAs signature as biomarkers of exposure to plasticizers.

Integrated transcriptome and proteome analysis indicates potential biomarkers of prostate cancer in offspring of pregnant rats exposed to a phthalate mixture during gestation and lactation.

As the second leading cause of death for cancer among men worldwide, prostate cancer (PCa) prevention and detection remain a critical challenge. One aspect of PCa research is the identification of common environmental agents that may increase the risk of initiation and progression of PCa. Endocrine disrupting chemicals (EDCs) are strong candidates for risk factors, partially because they alter essential pathways for prostate gland development and oncogenesis. Phthalates correspond to a set of commercially used plasticizers that humans are exposed to ubiquitously. Here, we show that maternal exposure to a phthalate mixture interferes with the expression profile of mRNA and proteins in the ventral prostate of offspring and increases the susceptibility to prostate adenocarcinomas in aged animals. The data highlight Ubxn11, Aldoc, Kif5c, Tubb4a, Tubb3, Tubb2, Rab6b and Rab3b as differentially expressed targets in young and adult offspring descendants (PND22 and PND120). These phthalate-induced targets were enriched for pathways such as: dysregulation in post-translational protein modification (PTPM), cell homeostasis, HSP90 chaperone activity, gap junctions, and kinases. In addition, the Kif5c, Tubb3, Tubb2b and Tubb4a targets were enriched for impairment in cell cycle and GTPase activity. Furthermore, these targets showed strong relationships with 12 transcriptional factors (TF), which regulate the phosphorylation of eight protein kinases. The correlation of TF-kinases is associated with alterations in immune system, RAS/ErbB/VEGF/estrogen/HIF-1 signaling pathways, cellular senescence, cell cycle, autophagy, and apoptosis. Downregulation of KIF5C, TUBB3 and RAB6B targets is associated with poor prognosis in patients diagnosed with adenocarcinoma. Collectively, this integrative investigation establishes the post-transcriptional mechanisms in the prostate that are modulated by maternal exposure to phthalate mixture during gestation and lactation.

EDC-2: The Endocrine Society's Second Scientific Statement on Endocrine-Disrupting Chemicals.

The Endocrine Society's first Scientific Statement in 2009 provided a wake-up call to the scientific community about how environmental endocrine-disrupting chemicals (EDCs) affect health and disease. Five years later, a substantially larger body of literature has solidified our understanding of plausible mechanisms underlying EDC actions and how exposures in animals and humans-especially during development-may lay the foundations for disease later in life. At this point in history, we have much stronger knowledge about how EDCs alter gene-environment interactions via physiological, cellular, molecular, and epigenetic changes, thereby producing effects in exposed individuals as well as their descendants. Causal links between exposure and manifestation of disease are substantiated by experimental animal models and are consistent with correlative epidemiological data in humans. There are several caveats because differences in how experimental animal work is conducted can lead to difficulties in drawing broad conclusions, and we must continue to be cautious about inferring causality in humans. In this second Scientific Statement, we reviewed the literature on a subset of topics for which the translational evidence is strongest: 1) obesity and diabetes; 2) female reproduction; 3) male reproduction; 4) hormone-sensitive cancers in females; 5) prostate; 6) thyroid; and 7) neurodevelopment and neuroendocrine systems. Our inclusion criteria for studies were those conducted predominantly in the past 5 years deemed to be of high quality based on appropriate negative and positive control groups or populations, adequate sample size and experimental design, and mammalian animal studies with exposure levels in a range that was relevant to humans. We also focused on studies using the developmental origins of health and disease model. No report was excluded based on a positive or negative effect of the EDC exposure. The bulk of the results across the board strengthen the evidence for endocrine health-related actions of EDCs. Based on this much more complete understanding of the endocrine principles by which EDCs act, including nonmonotonic dose-responses, low-dose effects, and developmental vulnerability, these findings can be much better translated to human health. Armed with this information, researchers, physicians, and other healthcare providers can guide regulators and policymakers as they make responsible decisions.

Executive Summary to EDC-2: The Endocrine Society's Second Scientific Statement on Endocrine-Disrupting Chemicals.

This Executive Summary to the Endocrine Society's second Scientific Statement on environmental endocrine-disrupting chemicals (EDCs) provides a synthesis of the key points of the complete statement. The full Scientific Statement represents a comprehensive review of the literature on seven topics for which there is strong mechanistic, experimental, animal, and epidemiological evidence for endocrine disruption, namely: obesity and diabetes, female reproduction, male reproduction, hormone-sensitive cancers in females, prostate cancer, thyroid, and neurodevelopment and neuroendocrine systems. EDCs such as bisphenol A, phthalates, pesticides, persistent organic pollutants such as polychlorinated biphenyls, polybrominated diethyl ethers, and dioxins were emphasized because these chemicals had the greatest depth and breadth of available information. The Statement also included thorough coverage of studies of developmental exposures to EDCs, especially in the fetus and infant, because these are critical life stages during which perturbations of hormones can increase the probability of a disease or dysfunction later in life. A conclusion of the Statement is that publications over the past 5 years have led to a much fuller understanding of the endocrine principles by which EDCs act, including nonmonotonic dose-responses, low-dose effects, and developmental vulnerability. These findings will prove useful to researchers, physicians, and other healthcare providers in translating the science of endocrine disruption to improved public health.

In vitro re-expression of the aryl hydrocarbon receptor (Ahr) in cultured Ahr-deficient mouse antral follicles partially restores the phenotype to that of cultured wild-type mouse follicles.

BACKGROUND: The aryl hydrocarbon receptor (AHR) mediates the toxic effects of various endocrine disrupting chemicals. In female mice, global deletion of the Ahr (AhrKO) results in slow growth of ovarian antral follicles. No studies, however, have examined whether injection of the Ahr restores the phenotypes of cultured AhrKO ovarian antral follicles to wild-type levels. METHODS: We developed a system to construct a recombinant adenovirus containing the Ahr to re-express the Ahr in AhrKO granulosa cells and whole antral follicles. We then compared follicle growth and levels of factors in the AHR signaling pathway (Ahr, Ahrr, Cyp1a1, and Cyp1b1) in wild-type, AhrKO, and Ahr re-expressed follicles. Further, we compared the response to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in wild-type, AhrKO, and Ahr re-expressed follicles. RESULTS: Ahr injection into AhrKO follicles partially restored their growth pattern to wild-type levels. Further, Ahr re-expressed follicles had significantly higher levels of Ahr, Ahrr, Cyp1a1, and Cyp1b1 compared to wild-type follicles. Upon TCDD treatment, only Cyp1a1 levels were significantly higher in Ahr re-expressed follicles compared to the levels in wild-type follicles. CONCLUSION: Our system of re-expression of the Ahr partially restores follicle growth and transcript levels of factors in the AHR signaling pathway to wild-type levels.

Correlates of sexual functioning among mid-life women.

OBJECTIVE: Studies have reported a decline in sexual functioning among women undergoing the menopausal transition. Few studies, however, have examined the associations between hormones and sexual dysfunction during this time period. Therefore, the purpose of this study was to examine the associations between participant characteristics and endogenous hormones with sexual functioning in mid-life women. METHODS: Data were analyzed from a community-based sample of 441 women aged 45-54 years who stated that they were sexually active at the time of the study. Each participant completed a survey that included questions pertaining to sexual functioning and provided a blood sample that was used to measure estrogen and androgen concentrations. RESULTS: Among women who reported being sexually active, poorer self-reported health and the experiencing of depressive symptoms were significantly associated with not being satisfied with sexual relations after adjustment for other covariates. None of the hormones examined were significantly associated with overall sexual satisfaction. However, statistically significant associations between both total testosterone levels and the free testosterone index with satisfaction with the frequency of sexual relations were observed. CONCLUSIONS: Our findings indicate that the experiencing of depressive symptoms and the reporting of poor overall health are important correlates of sexual dysfunction. Further, our results suggest that higher total and free testosterone levels are significantly associated with a desire for increased frequency of sexual relations among mid-life women.

Relation of body mass and sex steroid hormone levels to hot flushes in a sample of mid-life women.

OBJECTIVE: Previous studies indicate that obesity is associated with a higher risk of experiencing hot flushes in mid-life women. The reasons for this association are unknown, although altered hormone levels have been associated with both hot flushes and obesity. Thus, this current study tested the hypothesis that obesity is associated with hot flushes in mid-life women through a mechanism involving levels of total and free androgen, free estrogen, progesterone, and sex hormone binding globulin (SHBG). METHODS: Women aged 45-54 years were recruited from Baltimore and its surrounding counties. Each participant (n=628) was weighed, measured, completed a questionnaire, and provided a blood sample that was used to measure estradiol, estrone, testosterone, androstenedione, dehydroepiandrosterone sulfate, progesterone, and SHBG. RESULTS: Obese mid-life women (body mass index (BMI)>or=30.0 kg/m2) had significantly higher testosterone, and lower estradiol, estrone, progesterone, and SHBG levels than normal-weight mid-life women (BMI

Methoxychlor causes mitochondrial dysfunction and oxidative damage in the mouse ovary.

Methoxychlor (MXC) is an organochlorine pesticide that reduces fertility in female rodents by causing ovarian atrophy, persistent estrous cyclicity, and antral follicle atresia (apoptotic cell death). Oxidative damage resulting from reactive oxygen species (ROS) generation has been demonstrated to lead to toxicant-induced cell death. Thus, this work tested the hypothesis that MXC causes oxidative damage to the mouse ovary and affects mitochondrial respiration in a manner that stimulates ROS production. For the in vitro experiments, mitochondria were collected from adult cycling mouse ovaries, treated with vehicle (dimethyl sulfoxide; DMSO) or MXC, and subjected to polarographic measurements of respiration. For the in vivo experiments, adult cycling CD-1 mice were dosed with either vehicle (sesame oil) or MXC for 20 days. After treatment, ovarian mitochondria were isolated and subjected to measurements of respiration and fluorimetric measurements of H2O2 production. Some ovaries were also fixed and processed for immunohistochemistry using antibodies for ROS production markers: nitrotyrosine and 8-hydroxy-2'-deoxyguanosine (8-OHG). Ovaries from in vivo experiments were also used to measure the mRNA expression and activity of antioxidants such as Cu/Zn superoxide dismutase (SOD1), glutathione peroxidase (GPX), and catalase (CAT). The results indicate that MXC significantly impairs mitochondrial respiration, increases production of H2O2, causes more staining for nitrotyrosine and 8-OHG in antral follicles, and decreases the expression and activity of SOD1, GPX, and CAT as compared to controls. Collectively, these data indicate that MXC inhibits mitochondrial respiration, causes ROS production, and decreases antioxidant expression and activity in the ovary, specifically in the antral follicles. Therefore, it is possible that MXC causes atresia of ovarian antral follicles by inducing oxidative stress through mitochondrial production of ROS.

The effects of endocrine disrupting chemicals on the ovary.

Endocrine disrupting chemicals (EDCs) are natural or synthetic chemicals that mimic, enhance, or inhibit endogenous hormones. In this article, we review possible targets of EDCs within the ovary and explore whether EDCs may be acting as estrogen mimics, interfering with apoptosis, altering cell signaling pathways, or affecting estrogen metabolism. Though the study of EDCs has remained controversial, it is important to study them because our society continues to release large amounts of industrial chemicals into our environment and uncovering the mechanisms of action may lead to treatments of any potential adverse effects. In addition, studying how EDCs affect the ovary may lead to serendipitous discoveries about ovarian function and dysfunction. Finally, understanding the science behind endocrine disruption may influence the political and regulatory handling of EDCs.

Methoxychlor may cause ovarian follicular atresia and proliferation of the ovarian epithelium in the mouse.

Methoxychlor (MXC) is currently used to protect agricultural products from insects. Previous studies show that MXC adversely affects the ovary, but the target cells were not revealed by those studies. Therefore, the purpose of this study was to test the hypothesis that MXC induces ovarian changes by adversely affecting the antral follicles and the ovarian surface epithelium in the mouse. To test this hypothesis, cycling female CD-1 mice (39 days) were dosed with MXC (8, 16, or 32 mg/kg/day), kepone (KPN, 8 mg/kg/day, positive control), or sesame oil (vehicle control) via intraperitoneal injection for 10 or 20 days. Estrous cyclicity was evaluated daily via vaginal lavage. After dosing, ovaries were collected for histological evaluation of follicle numbers, atresia, and surface epithelial height. The results indicate that at the 20-day time point, MXC (32 mg/kg) and KPN (8 mg/kg) increased the percentage of atretic antral follicles (n= 4-9,p

Smad 3 may regulate follicular growth in the mouse ovary.

Although Smad 3 is known to serve as a signaling intermediate for the transforming growth factor beta (TGFbeta) family in nonreproductive tissues, its role in the ovary is unknown. Thus, we used a recently generated Smad 3-deficient (Smad 3-/-) mouse model to test the hypothesis that Smad 3 alters female fertility and regulates the growth of ovarian follicles from the primordial stage to the antral stage. In addition, we tested whether Smad 3 affects the levels of proteins that control apoptosis, survival, and proliferation in the ovarian follicle. To test this hypothesis, breeding studies were conducted using Smad 3-/- and wild-type mice. In addition, ovaries were collected from Smad 3-/- and wild-type mice on Postnatal Days 2-90. One ovary from each animal was used to estimate the total number of primordial, primary, and antral follicles. The other ovary was used for immunohistochemical analysis of selected members of the B-cell lymphoma/leukemia-2 family of protooncogenes (Bax, Bcl-2, Bcl-x), proliferating cell nuclear antigen (PCNA), and cyclin-dependent kinase 2 (Cdk-2). The results indicate that Smad 3-/- mice have reduced fertility compared with wild type mice. The results also indicate that Smad 3 may not affect the size of the primordial follicle pool at birth, but it may regulate growth of primordial follicles to the antral stage. Further, the results indicate that Smad 3 may regulate the expression of Bax and Bcl-2, but not Bcl-x, Cdk-2, and PCNA. Collectively, these data suggest that Smad 3 may play an important role in the regulation of ovarian follicle growth and female fertility.

Hormone replacement therapy and breast cancer: a qualitative review.

OBJECTIVE: To assess whether recent epidemiologic evidence supports an association between use of estrogen replacement therapy or hormone replacement therapy and risk of breast cancer. DATA SOURCES: The keywords "estrogen," "estrogen replacement therapy," or "hormone replacement therapy," and "breast cancer" or "breast neoplasm," were used to search for articles published from 1975-2000 in MEDLINE and Dialogweb. Only articles published in peer-reviewed journals and containing original data were included in this review. METHODS: Unadjusted or age-adjusted risk estimates for breast cancer among ever users of estrogen therapy compared with never users were abstracted from published articles or calculated using the data provided in the published reports. TABULATION, INTEGRATION, AND RESULTS: We found little consistency among studies that estimated the risk of breast cancer in hormone users compared with nonusers and in studies assessing the risk by duration of use. However, there was consistently a lower risk of death from breast cancer in hormone users compared with nonusers. CONCLUSION: The evidence did not support the hypotheses that estrogen use increases the risk of breast cancer and that combined hormone therapy increases the risk more than estrogen only. Additional observational studies are unlikely to alter this conclusion. Although a small increase in breast cancer risk with hormone therapy or an increased risk with long duration of use (15 years or more) cannot be ruled out, the likelihood of this must be small, given the large number of studies conducted to date.

Media coverage of women's health issues: is there a bias in the reporting of an association between hormone replacement therapy and breast cancer?

Media coverage of scientific research plays a major role in shaping public opinion and influencing medical practice. When an association is controversial, such as with hormone replacement therapy (HRT) and breast cancer, it is important that a balanced picture of the scientific literature be reported. The objective of this study was to assess whether scientific publications that do and do not support an HRT/breast cancer association were cited in the media in proportions similar to those with which they appear in the scientific literature. Scientific publications reporting on the HRT/breast cancer association published from January 1, 1995, to June 30, 2000, were identified through a systematic Medline search. Media reports from newspapers, magazines, television, and radio that reported on HRT and breast cancer were retrieved from an online database. Investigators independently recorded characteristics of the scientific publications and media reports. A total of 32 scientific publications were identified: 20 (62.5%) concluded there was an increased risk of breast cancer associated with HRT (positive publications), and 12 (37.5%) concluded there was no evidence for an association (null publications). Nearly half (47%) of the scientific publications were not cited by the media. There were 203 media citations of scientific publications: 82% were of positive publications and 18% were of null publications, representing a significant excess of citations of positive publications (p < 0.01). Media coverage of this controversial issue is based on a limited sample of the scientific publications. Moreover, the excess of media citations for positive scientific publications suggests a bias against null scientific publications.

Ethnic differences in cancer mortality trends in the US, 1950-1992.

OBJECTIVE: To describe long-term mortality trends by ethnicity, sex, and age for selected cancers and to assess the effect of age-adjustment using different standard populations on rate ratios and rate differences comparing black to white cancer mortality. DESIGN: Mortality rates for selected cancers were obtained from published reports of the Vital Statistics of the United States (1950-1992). All ethnic- and sex-specific cancer rates were directly age-adjusted to the total 1970 US standard population and to a subset of the 1970 US standard population 40 years and older. RESULTS: Over a 42-year period, lung cancer mortality increased in all population subgroups. Colorectal cancer mortality declined in whites, but increased in blacks. Prostate cancer mortality increased slightly in white men, but dramatically increased in black men. Breast cancer mortality stabilized in white women, but increased markedly in black women. Uterine cancer mortality declined for both ethnicities, while ovarian cancer mortality rates increased for both ethnicities. As expected, the ratios of the age-adjusted cancer mortality rates comparing blacks to whites were the same regardless of the age structure used as the standard population. In contrast, the differences in the age-adjusted rates between blacks and whites were greater when the age-truncated standard population was used. CONCLUSIONS: There are unexplained ethnic differences in the long-term mortality trends of selected cancers. Of particular concern are the increasing death rates in black individuals from colorectal, prostate, breast, and ovarian cancers. Since almost all deaths from these cancers occur in persons over 40, age-adjustment using an age-truncated standard population that includes only those age groups at risk should be considered, particularly when the question to be addressed is one dealing with the impact of a characteristic, such as ethnicity or sex, on mortality risk.

Non-high-density lipoprotein cholesterol level as a predictor of cardiovascular disease mortality.

BACKGROUND: Non-high-density lipoprotein cholesterol (non-HDL-C) contains all known and potential atherogenic lipid particles. Therefore, non-HDL-C level may be as good a potential predictor of risk for cardiovascular disease (CVD) as low-density lipoprotein cholesterol (LDL-C). OBJECTIVES: To determine whether non-HDL-C level could be useful in predicting CVD mortality and to compare the predictive value of non-HDL-C and LDL-C levels. METHODS: Data are from the Lipid Research Clinics Program Follow-up Study, a mortality study with baseline data gathered from 1972 through 1976, and mortality ascertained through 1995. A total of 2406 men and 2056 women aged 40 to 64 years at entry were observed for an average of 19 years, with CVD death as the main outcome measure. RESULTS: A total of 234 CVD deaths in men and 113 CVD deaths in women occurred during follow-up. Levels of HDL-C and non-HDL-C at baseline were significant and strong predictors of CVD death in both sexes. In contrast, LDL-C level was a somewhat weaker predictor of CVD death in both. Differences of 0.78 mmol/L (30 mg/dL) in non-HDL-C and LDL-C levels corresponded to increases in CVD risk of 19% and 15%, respectively, in men. In women, differences of 0.78 mmol/L (30 mg/dL) in non-HDL-C and LDL-C levels corresponded to increases in CVD risk of 11% and 8%, respectively. CONCLUSIONS: Non-HDL-C level is a somewhat better predictor of CVD mortality than LDL-C level. Screening for non-HDL-C level may be useful for CVD risk assessment.

In utero and lactational treatment with 2,3,7,8-tetrachlorodibenzo-p-dioxin impairs mammary gland differentiation but does not block the response to exogenous estrogen in the postpubertal female rat.

These experiments tested whether in utero and lactational exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) alters mammary gland differentiation, estrogen receptor alpha (ERalpha) expression levels, or the response to estrogen in the female postpubertal rat mammary gland. Pregnant Holtzman rats were administered a single oral dose of 1 microg/kg TCDD or vehicle on gestation-day 15. Exposed and non-exposed female offspring were weaned on postnatal day 21 and ovariectomized at 9 weeks of age. Two weeks later, both TCDD and control animals were divided into 3 groups, receiving treatment with placebo, 0.025, or 0.1 mg 17beta-estradiol pellet implants. After 48 h, mammary tissue was removed for analysis following euthanasia. TCDD-exposed mammary glands demonstrated impaired differentiation as measured by the distribution of terminal ductal structures and increased expression levels of ERalpha. The response to exogenous estrogen was tested in TCDD-exposed animals and compared to control non-exposed animals. Estrogen stimulation of the TCDD-exposed glands induced progesterone receptor expression and mammary gland differentiation as measured by a shift in distribution from terminal end buds and terminal ducts to Types I and II lobules. Control glands were better differentiated at baseline and did not exhibit any significant changes in the distribution of terminal ductal structures following estrogen stimulation. The increase in progesterone receptor-expression levels by exogenous estrogen in control glands was similar to the TCDD-exposed glands. These experiments demonstrate that in utero and lactational exposures to TCDD impair mammary gland differentiation but that TCDD-exposed mammary glands retain the ability to differentiate in response to estrogen.

Effect of bcl-2 on the primordial follicle endowment in the mouse ovary.

Little is known about the embryonic factors that regulate the size of the primordial follicle endowment at birth. A few studies suggest that members of the B-cell lymphoma/leukemia-2 (bcl-2) family of protooncogenes may be important determinants. Thus, the purpose of this study was to test whether bcl-2 regulates the size of the primordial follicle pool at birth. To test this hypothesis, three lines of transgenic mice (c-kit/bcl-2 mice) were generated that overexpress human bcl-2 in an effort to reduce prenatal oocyte loss. The overexpression was targeted to the ovary and appropriate embryonic time period with the use of a 4.8-kilobase c-kit promoter. This promoter provided two to three times more expression of bcl-2 in the ovaries with minimal or no overexpression in most nongonadal tissues. On Postnatal Days 8-60, ovaries were collected from homozygous c-kit/bcl-2 and nontransgenic littermates (controls) and processed for histological evaluation of follicle numbers. All lines of c-kit/bcl-2 mice were born with significantly more primordial follicles than control mice (P < or = 0.05). By Postnatal Days 30-60, however, there were no significant differences in follicle numbers between c-kit/bcl-2 and control mice. These results indicate that bcl-2 overexpression increases the number of primordial follicles at birth, but that the surfeit of primordial follicles is not maintained in postnatal life. These data suggest that it is possible that the ovary may contain a census mechanism by which excess numbers of primordial follicles at birth are detected and removed from the ovary by adulthood.

Bcl-x and Bax regulate mouse primordial germ cell survival and apoptosis during embryogenesis.

Restricted germ cell loss through apoptosis is initiated in the fetal gonad around embryonic day 13.5 (E13.5) as part of normal germ cell development. The mechanism of this germ cell attrition is unknown. We show that Bcl-x plays a crucial role in maintaining the survival of mouse germ cells during gonadogenesis. A bcl-x hypomorphic mouse was generated through the introduction of a neomycin (neo) gene into the promoter of the bcl-x gene by homologous recombination. Mice that contained two copies of the hypomorphic allele had severe reproductive defects attributed to compromised germ cell development. Males with two mutant alleles lacked spermatogonia and were sterile; females showed a severely reduced population of primordial and primary follicles and exhibited greatly impaired fertility. Primordial germ cells (PGCs) in bcl-x hypomorph mice migrated to the genital ridge by E12.5 but were depleted by E15.5, a time when Bcl-x and Bax were present. Two additional bcl-x transcripts were identified in fetal germ cells more than 300 bp upstream of previously reported start sites. Insertion of a neo cassette led to a down-regulation of the bcl-x gene at E12.5 in the hypomorph. Bax was detected by immunohistochemistry in germ cells from bcl-x hypomorph and control testes at E12.5 and E13.5. Bcl-x function was restored, and animals of both genders were fertile after removal of the neo selection cassette using Cre-mediated recombination. Alternatively, the loss of Bcl-x function in the hypomorph was corrected by the deletion of both copies of the bax gene, resulting in a restoration of germ cell survival. These findings demonstrate that the balance of Bcl-x and Bax control PGC survival and apoptosis.