Impact of Endocrine‐Disrupting Chemicals on Reproductive Function in Zebrafish (Danio rerio)

The prevalence of endocrine‐disrupting chemicals (EDCs) in the aquatic environment has been associated with the wide detection of alterations in the development and physiology of vertebrates. Zebrafish, as a model species, has been extensively used in toxicological research. In this review, we focus on recent published evidence of the harmful effects of EDCs on reproductive function in zebrafish, including skewed sex ratio, immature gonads, diminished sexual behaviour, decreased sperm count, reduced spawning and fertilization. These impairments mostly result from disruption to sex‐steroid hormones induced by endocrine disruptors. We also discuss other effects of exposure to EDCs. In EDC exposure research, despite incomplete assessments of altered gonad histopathology and sexual behaviour, these present potential effective biomarkers or pathways for evaluating the reproductive function in zebrafish on EDC exposure. To date, the pernicious effects of some EDCs on the reproductive performance in laboratory zebrafish are well understood; however, similar alterations remain for further determination in wild‐type fish and more kinds of EDCs. More studies should be performed under established scientific regulatory criteria to investigate the impact of EDCs on reproduction in zebrafish. Moreover, further research is required to explain the definite mechanism of sexual differentiation, which helps in understanding the shift of sexual phenotype with EDC exposure.     

Risk assessment of endocrine-active compounds in feeds

As a key element of the 'farm-to-fork' approach, an assessment of the safety of feed components should consider major long-term toxicological hazards, such as endocrine disrupting chemicals (EDCs). In this review, attention is given to endocrine-modulating trace elements (such as iodine and trivalent chromium) and their potentially sensitive subgroups as nutritional feed additives from the standpoint of farm animal safety and consumer exposure. Feedstuffs can be a major vehicle for persistent EDCs, such as polychlorinated biphenyls, and potential risks include fish farming and ruminants grazing in polluted areas. Limited data still exist on the feed-to-food transfer of other EDCs, such as brominated flame retardants. EDCs of vegetable origin (e.g. zearalenone and isothiocyanates) can have a greater adverse impact on farm animals than environmental xenobiotics but the risk of carry-over to consumers appears low. Topics for further research are suggested, including the need for more refined exposure data, characterization of biomarkers for long-term effects, xenobiotic-nutrient interactions and the search for novel feed ingredients that are less vulnerable to contamination.     

Effects of Endocrine Disrupting Compounds in Animal Feed on Reproductive Health in Farm Animals*Euroconference Wageningen, The Netherlands, 20–22nd November 1998

This Euroconference was a follow-up to the Euroconference held in Halle, April 1997. The programme of the conference in Halle had an exploratory character with respect to accumulation of endocrine disrupting compounds (EDCs) in the environment and in animal tissues and their effects on animal physiology and reproduction. Many questions arose from the first Euroconference, such as: What are biologically meaningful levels of environmental contamination? Is there a risk for farm animals’ health and reproduction? What assays are available and which are the most appropriate to be used? These questions formed the basis for the programme of the second Euroconference held in Wageningen in November 1998. Taking these questions into consideration, the programme of the Wageningen Euroconference was divided into four main topics. In the first session an overview was given on sources and levels of EDCs in the environment. The second session addressed chemical nature and metabolism of EDCs including phytoestrogens. In the third session the effects of EDCs on ovarian function and embryo development were discussed and in the last session the advantages and disadvantages of different in vivo as well as in vitro assays were debated.     

Effects of maternal diet and exposure to bisphenol A on sexually dimorphic responses in conceptuses and offspring

Whereas sexual differentiation is considered as the onset of differentiation of the male or female gonads, mounting evidence indicates that sex differences in developmental programming are established as early as the zygotic stage. Genetic and epigenetic differences between the sexes might govern how each responds to shifts in their early environment, including in the uterus or culture dish, as in the case of in vitro cultured pre-implantational embryos. Even if no differences are evident between the sexes at birth, divergent conceptus responses to surrounding changes, such as maternal diet and exposure to endocrine disrupting compounds (EDC), such as bisphenol A (BPA), might predispose one sex over the other to later adult-onset diseases, otherwise termed developmental origin of health and disease (DOHaD). Overall, males subjected to less than optimal in utero conditions tend to be at greater risk for various diseases, including neurobehavioural disorders. As the placenta is the primary nutrient acquisition and communication organ between the dam and foetus, its ability to adapt rapidly to environmental shifts might buffer the conceptus against environmental insults. The placenta of one sex over the other might possess greater ability to respond to environmental fluctuations. In utero environmental changes, including maternal nutrient excess or reduction or exposure to the EDC, BPA, might govern sex-dependent behavioural alterations. In sum, this review examines the evidence to date that male and female zygotes and conceptuses diverge in their responses to shifting environmental conditions and whether these contrasting sexually dimorphic responses underpin later DOHaD outcomes, namely neurobehavioural changes.     

Epigenetics and transgenerational inheritance in domesticated farm animals

Epigenetics provides a molecular mechanism of inheritance that is not solely dependent on DNA sequence and that can account for non-Mendelian inheritance patterns. Epigenetic changes underlie many normal developmental processes, and can lead to disease development as wel. While epigenetic effects have been studied in wel-characterized rodent models, less research has been done using agricultural y important domestic animal species. This review wil present the results of current epigenetic research using farm animal models(cattle, pigs, sheep and chickens). Much of the work has focused on the epigenetic effects that environmental exposures to toxicants, nutrients and infectious agents has on either the exposed animals themselves or on their direct offspring. Only one porcine study examined epigenetic transgenerational effects; namely the effect diet micronutrients fed to male pigs has on liver DNA methylation and muscle mass in grand-offspring(F2 generation). Healthy viable offspring are very important in the farm and husbandry industry and epigenetic differences can be associated with production traits. Therefore further epigenetic research into domestic animal health and how exposure to toxicants or nutritional changes affects future generations is imperative.     

Epigenetics and transgenerational inheritance in domesticated farm animals

Epigenetics provides a molecular mechanism of inheritance that is not solely dependent on DNA sequence and that can account for non-Mendelian inheritance patterns. Epigenetic changes underlie many normal developmental processes, and can lead to disease development as well. While epigenetic effects have been studied in well-characterized rodent models, less research has been done using agriculturally important domestic animal species. This review will present the results of current epigenetic research using farm animal models (cattle, pigs, sheep and chickens). Much of the work has focused on the epigenetic effects that environmental exposures to toxicants, nutrients and infectious agents has on either the exposed animals themselves or on their direct offspring. Only one porcine study examined epigenetic transgenerational effects; namely the effect diet micronutrients fed to male pigs has on liver DNA methylation and muscle mass in grand-offspring (F2 generation). Healthy viable offspring are very important in the farm and husbandry industry and epigenetic differences can be associated with production traits. Therefore further epigenetic research into domestic animal health and how exposure to toxicants or nutritional changes affects future generations is imperative.     

Are Endocrine Disrupting Compounds a Threat to Farm Animal Health,Welfare and Productivity?

Contents The sources and characteristics of endocrine disrupting compounds (EDCs) are reviewed and discussed with respect to their potential effects on farm animal health, welfare and productivity. The importance of certain properties of these compounds in relation to the expression of their biological effects is addressed together with potential routes of exposure. It is concluded that little is known of factors affecting the tissue concentrations of EDCs in farm animals, the concentrations that are required to perturb physiological function in these species, the effects of prolonged exposure to low doses, the effect of cocktails of EDCs and other pollutants or the responses of specific organs and physiological systems that are affected by EDCs. Much of the available information pertaining to EDCs is derived from epidemiological studies of wildlife species and from laboratory animal studies and while these studies have significant limitations, they are considered to be valuable indicators of potential effects in farm animal species. The results of such studies, together with the small amounts of data from studies of ruminants, indicate that there may be significant effects of exposure to environmental levels of EDCs on farm animal health, even although effects are not generally apparent in practice, at this time.     

牧草表观遗传学研究进展

表观遗传是指在DNA序列不变的情况下基因表达发生变化的现象。表观遗传现象与外界环境条件的变化紧密相关,它参与植物的生长发育、胁迫响应、衰老死亡等重要生命过程并在其中起到了关键作用。表观遗传学作为一门新兴学科在近20年间得到了快速发展,成为当前动植物和医学领域的研究热点。目前植物表观遗传学的相关研究主要集中在DNA甲基化、组蛋白修饰、RNA甲基化、染色质重塑和非编码RNA修饰等方面,并取得了许多重要成果。然而,相对于模式植物拟南芥和其他主要作物而言,牧草的表观遗传学研究仍处于起步阶段。因此,开展牧草表观遗传学研究对我国草牧业的可持续发展具有重要意义。本研究对表观遗传学的概念、研究方法、研究内容(包括DNA甲基化、组蛋白修饰、RNA甲基化、染色质重塑和非编码RNA修饰等)及牧草表观遗传学相关研究进行了全面总结和综述,并对表观遗传在草牧业中的发展前景进行了展望。     

Is exposure to endocrine disrupting compounds during fetal/post-natal development affecting the reproductive potential of farm animals?

Concerns have been raised about the potential adverse effects on reproductive health and immune status of farm animals following exposure to a range of natural and synthetic environmental compounds that disrupt normal hormonal actions. These compounds range from natural plant oestrogens (e.g. genistein, coumesterol) and mycoestrogens (e.g. Aflatoxins, zearalenone) to growth promoting pharmaceuticals (e.g. trenbolone acetate, melengastrol acetate) to chemicals spread in water, sewage sludge or the atmosphere such as detergents and surfactants (e.g. octylphenol, nonylphenol), plastics (e.g. bisphenol-A, phthalates), pesticides (e.g. methoxychlor, dieldrin, DDT) and industrial chemicals (e.g. PCB, TCDD). These compounds are commonly termed 'endocrine disrupting compounds' (EDCs) or 'endocrine disruptors' due to their ability to act as either hormone agonists or antagonists or the ability to disrupt hormone synthesis, storage or metabolism. A similar group of compounds are called 'immunotoxicants' and are thought to affect the immune system mainly by disrupting B and T cell homeostasis. As more studies are performed it is becoming clear that many compounds can directly or indirectly affect both the endocrine and immune systems. The susceptibility of target tissues is related to the stage of development, the cumulative exposure dose and the immune status of the individual. While some of the effects of the EDCs on the endocrine and immune systems are quite distinct, many are subtle and identifying the causative agent from the vast array of environmental challenges including EDCs, nutrition, temperature, etc. can be problematic. Identifying the causative agent is confounded by the possibility that effects that are observed in the adult may be due to exposure to EDCs during fetal life. This has major implications for the determination of universal end-point measurements to assess exposure to EDCs in farm animals.     

环境内分泌干扰物对睾丸间质细胞功能的影响

近年来,环境内分泌干扰物(environmental endocrine disrupting chemicals,EDCs)对雄性动物的生殖毒性引起了广泛的关注。大量资料显示EDCs可引起雄性生殖发育障碍,如隐睾、尿道下裂、睾丸癌、精液品质不良等。作者就几种典型的EDCs对睾丸间质细胞分泌睾酮的影响机制作一综述。     

Epigenetic assessment of environmental chemicals detected in maternal peripheral and cord blood samples

Epigenetic alteration is an emerging paradigm underlying the long-term effects of chemicals on gene functions. Various chemicals, including organophosphate insecticides and heavy metals, have been detected in the human fetal environment. Epigenetics by DNA methylation and histone modifications, through dynamic chromatin remodeling, is a mechanism for genome stability and gene functions. To investigate whether such environmental chemicals may cause epigenetic alterations, we studied the effects of selected chemicals on morphological changes in heterochromatin and DNA methylation status in mouse ES cells (ESCs). Twenty-five chemicals, including organophosphate insecticides, heavy metals and their metabolites, were assessed for their effect on the epigenetic status of mouse ESCs by monitoring heterochromatin stained with 4￠,6-diamino-2-phenylindole (DAPI). The cells were surveyed after 48 or 96 h of exposure to the chemicals at the serum concentrations of cord blood. The candidates for epigenetic mutagens were examined for the effect on DNA methylation at genic regions. Of the 25 chemicals, five chemicals (diethyl phosphate (DEP), mercury (Hg), cotinine, selenium (Se) and octachlorodipropyl ether (S-421)) caused alterations in nuclear staining, suggesting that they affected heterochromatin conditions. Hg and Se caused aberrant DNA methylation at gene loci. Furthermore, DEP at 0.1 ppb caused irreversible heterochromatin changes in ESCs, and DEP-, Hg- and S-421-exposed cells also exhibited impaired formation of the embryoid body (EB), which is an in vitro model for early embryos. We established a system for assessment of epigenetic mutagens. We identified environmental chemicals that could have effects on the human fetus epigenetic status.     

Differential effects of the endocrine-disrupting compounds bisphenol-A and octylphenol on gonadotropin secretion, in prepubertal ewe lambs

This study examined the effects of long-term exposure to the endocrine-disrupting compounds (EDCs) Bisphenol-A (BPA) and Octylphenol (OP) on gonadotrophin secretion in pre-pubertal female sheep. Four-week-old, female lambs were randomly allocated to four groups (n=6), and twice each week treated with i.m. injections of either corn oil (vehicle controls), diethylstilbestrol (DES; 0.175mg/kg), BPA (3.5mg/kg) or OP (3.5mg/kg). After 5 weeks of treatment, animals were ovariectomized (ovx) and ovary weights recorded. Two weeks later, blood samples were collected from lambs every 15min for 6h, for LH pulse analysis. Animals were then euthanased and adrenal and kidney weight recorded. An age-related increase in tonic LH secretion was noted in Control, BPA- and OP-treated lambs, but was absent in DES-treated lambs. Following ovx, LH secretion increased in all except DES-treated lambs; FSH concentrations increased in all groups. BPA and DES significantly suppressed LH pulse frequency (C: 6.7+/-0.3pulses/6h, DES: 1.5+/-0.8pulses/6h, BPA: 2.3+/-0.8pulses/6h) and amplitude (C: 7.1+/-1.0ng/ml, DES: 1.9+/-0.6ng/ml, BPA: 1.6+/-0.4ng/ml). OP had no effect on LH secretion (Frequency: 5.8+/-0.5pulses/6h, amplitude: 8.0+/-2.0ng/ml). Ovary weight was similar among all groups. Results show that chronic in vivo exposure of prepubertal female lambs to BPA, at levels lower than those reported previously, can have significant effects on LH secretion that are comparable to those seen following exposure to the known xenoestrogen, DES. Exposure to an equal dose of the EDC OP, over the equivalent period of time was without effect on gonadotropin secretion in the prepubertal ewe lamb. These results indicate that exposure of prepubertal female lambs to the EDC BPA can induce significant effects on gonadotropin secretion, the potential long-term effects of exposure and the effects of these changes on reproductive performance and efficacy, therefore, merit further study.     

Oocyte-somatic cell-endocrine interactions in pigs

Oocyte-somatic cell communication is bi-directional and essential for both oocyte and follicular granulosa and theca cell function and development. We have shown that the oocyte secretes factors that stimulate porcine granulosa cell proliferation in serum-free culture, and suppress progesterone production, thereby preventing premature luteinisation. Possible candidates for mediating some of these effects are the bone morphogenetic proteins (BMPs) that belong to the transforming growth factor beta family. They are emerging as a family of proteins critical for fertility and ovulation rate in several mammals, and they are expressed in various cell types in the ovary. We have evidence for a functional BMP system in the porcine ovary and BMP receptors are present in the egg nests in the fetal ovary and in the granulosa cells, oocytes and occasional theca cells throughout subsequent development. In addition to paracrine interactions in the ovary, the porcine oocyte and its developmental potential can also be influenced by nutritional manipulation in vivo. We have demonstrated that feeding a high plane of nutrition to gilts for 19 days prior to ovulation increased oocyte quality compared to control animals fed a maintenance diet, as determined by oocyte maturation in vitro. This was associated with a number of changes in circulating reproductive and metabolic hormones and also in the follicular fluid in which the oocyte is nurtured. Further studies showed a similar increase in prenatal survival on Day 30 of gestation, demonstrating a direct link between oocyte quality/maturation and embryo survival. Collectively, these studies emphasise the importance of the interactions that occur between the oocyte and somatic cells and also with endocrine hormones for ovarian development, and ultimately for the production of oocytes with optimal developmental potential.     

microRNA对动物生殖轴以及胚胎着床影响的研究进展

表观调控作为调节基因功能的一种重要手段,其对生殖内分泌方面的调控起着重要作用。microRNA(miRNA)作为一类小的非编码RNA,也是一种表观遗传因子,它广泛参与生物体内各种生理及病理过程,对哺乳动物繁殖起着重要的调控作用。本文围绕miRNA在哺乳动物繁殖相关组织的表达及调控作用和miRNA对胚胎着床的影响进行综述,为理解miRNA对繁殖方面的表观调控、改善哺乳动物繁殖能力提供理论基础。     

17α-甲基睾酮对稀有鮈鲫体内激素水平的影响

环境内分泌干扰物（EDCs）对动物和人的健康有一定的危害作用,很大一部分环境内分泌干扰物最终都进入到了水环境中,对水生生物的生殖、内分泌等系统造成损伤。以稀有鮈鲫作为毒性试验材料,选择具有代表性的雄激素17α-甲基睾酮（MT）作为研究对象,采用酶联免疫法（ELISA）研究MT处理7 d对稀有鮈鲫体内雌二醇（E2）、睾酮（T）和11-酮基睾酮（11-KT）含量的影响。结果显示,经MT处理7 d后,雌鱼体内的E2、T和11-KT含量均极显著高于对照组（P〈0.01）,而雄鱼体内的E2、T和11-KT含量均极显著低于对照组（P〈0.01）。     

双峰驼精清诱导排卵因子的研究进展

双峰驼具有独特的繁殖生理机能，是季节发情、诱导排卵的动物。文章对双峰驼繁殖特性和卵泡发育及诱导排卵因子的发现、分离和纯化、部分生物学性质等方面的研究进展进行了简要综述。     

Pulmonary fibrosis in response to environmental cues and molecular targets involved in its pathogenesis

Chronic lung injury resulting from a variety of different causes is frequently associated with the develop ment of pulmonary fibrosis in humans. Although the etiology of pulmonary fibrosis is generally unknown, several sources of evidence support the hypothesis that a number of environmental and occupational agents play an etiologic role in the pathogenesis of this disease. The agents discussed in this review include beryllium, nylon flock, textile printing aerosols, polyvinyl chloride and didecyldimethylammonium chloride. The authors also describe a variety of animal models, including genetically modified mice, in order to investigate the molecular mechanism of pulmonary fibrosis, focusing on chemokine receptors, regulatory T cells and transforming growth factor-β and bone morphogenetic protein signaling. Overall, we propose the concept of toxicological pulmonary fibrosis as a lung disease induced in response to environmental cues.     

Inhibin: Regulation of reproductive function and practical use in females

Inhibins are gonadal glycoprotein hormones selectively and potently inhibiting follicle‐stimulating hormone (FSH) secretion from the pituitary gland. Inhibins are produced mainly by the ovary and are purified from follicular fluid. Inhibins were shown to be produced in two forms through dimeric assembly of an α‐subunit and one of two closely related β‐subunits to form inhibin A (α‐βA) and inhibin B (α‐βB). Although inhibin subunits are expressed in various tissues, the gonads are the major source of circulating inhibins. While inhibins may act as a paracrine or autocrine factor in some tissues, their best understood roles are as endocrine regulators of pituitary FSH. In this review we focus our attention on more recent developments in inhibin research. We describe patterns of inhibin A and B secretion during the estrous cycle. We also review the immunization against inhibin α subunit as a practical method for superovulation. Superovulation has been induced successfully by passive or active immunization against the inhibin α‐subunit in several species such as mice, rats, hamsters, guinea pigs, cows, mares, ewes and goats. Furthermore, several studies have shown that oocytes superovulated with immunization against inhibin α‐subunit have the ability to develop normally, suggesting that inhibin immunization could be used as a practical method for superovulation in a wide range of animal species.     

Telegony,the Sire Effect and non‐Mendelian Inheritance Mediated by Spermatozoa: A Historical Overview and Modern Mechanistic Speculations

Telegony is the belief that the sire first mated to a female will have an influence upon some of that female’s later offspring by another male. Although the reality of telegony was acknowledged by such authorities as Darwin, Spencer, Romanes and many experienced breeders, it has been met with scepticism because of Weismann’s unfavourable comments and negative results obtained in several test experiments. In this article, alleged cases of telegony are provided. A search of the literature of cell biology and biochemistry reveals several plausible mechanisms that may form the basis for telegony. These involve the penetration of spermatozoa into the somatic tissues of the female genital tract, the incorporation of the DNA released by spermatozoa into maternal somatic cells, the presence of foetal DNA in maternal blood, as well as sperm RNA‐mediated non‐Mendelian inheritance of epigenetic changes.     

Consequences of endocrine disrupting chemicals on reproductive endocrine function in birds: establishing reliable end points of exposure

It has been difficult to establish reliable indices of exposure to endocrine disrupting chemicals (EDCs) appropriate for a variety of avian species because of a vast array of reproductive strategies. Data from mammals, reptiles and fish provide insight on likely mechanisms of action for EDCs. However, many of the effects of EDCs are weaker than the actions of the native hormones, making it difficult to assess adverse effects in domestic and wild birds. It is clear that differential sensitivity to EDCs exists across species, due to the timing and mode of exposure, compound toxicity and age of the individual. Our studies on EDCs are conducted in the quail model system, with focus on reproductive endocrine, neuroendocrine and behavioral responses. Studies have included EDC exposure, either by egg injection or via diet. Results from egg injection studies showed the following: (1) estradiol administered by embryonic day 12 demasculinized male sexual behavior, altered hypothalamic neurotransmitters and reduced hen day production and fertility in a dose dependent fashion, (2) methoxychlor (MXC) or vinclozolin impaired male sexual behavior in adult quail and (3) DDE exposure impaired reproductive and immune related end points. Two-generation studies were conducted on Japanese and northern bobwhite quail with dietary methoxychlor (MXC) exposure (0, 5 and 10 ppm) beginning in adults (P1), continuing in their offspring (F1), with F2 offspring raised on control diet. MXC exposure impaired male sexual behavior, hypothalamic catecholamines and plasma steroid hormones. Moreover, MXC exposure had reproductive consequences observable at both the lower and higher doses of MXC in F1 and F2 generations. These data demonstrate that embryonic EDC exposure interferes with sexual differentiation of neural systems that direct reproduction.