Procedure for rapid oocyte selection based on quantitative analysis of cumulus cell gene expression

PURPOSE

To develop a procedure for the analysis of gene expression in cumulus cells during the interval between ovum pick up and insemination to select the best oocytes for fertilization.

METHODS

Five RNA extraction methods, three reverse transcription procedures followed by Real-time quantitative PCR and one single-step mRNA quantification kit were tested to measure the expression of five genes in cumulus cells.

RESULTS

Two RNA extraction kits gave the best combination of efficiency and purity. One reverse transcription procedure gave the best speed and efficiency. The single-step kit required more biological material than would be available from single cumulus oocyte complexes (COCs).

CONCLUSIONS

Our test identified a combination of RNA extraction and reverse transcription procedures that enables the level measurement of 5 selected cumulus cell transcripts within 4 h. Using this combination it was possible to obtain a reliable quantification of gene expression in 44 out of 46 individual COCs collected from seven patients.

Effects of pre-mating nutrition on mRNA levels of developmentally relevant genes in sheep oocytes and granulosa cells

The present study was designed to investigate the relationship between pre-mating nutrition and the relative amounts of a panel of developmentally relevant genes in ovine oocytes and granulosa cells. Cast age ewes were fed a ration providing 0.5x (0.5 M) or 1.5x (1.5 M) live weight maintenance requirements for 2 weeks before slaughter. The ewes were synchronized and superovulated with FSH and pregnant mares serum gonadotropin. At slaughter, oocytes and granulosa cells were aspirated from follicles >2 mm in diameter and the relative abundance of 8 and 17 transcripts in oocytes and granulosa cells respectively were analyzed by semi-quantitative RT-PCR. In the oocytes, no differences between groups were observed for five transcripts (GDF9, BMP15, c-kit, glucose transporter 1 (SLC2A1), and hexokinase 1), but a lower amount of glucose transporter 3 (SLC2A3), sodium/glucose cotransporter 1 (SLC5A1), and Na(+)/K(+) ATPase mRNAs was detected in the 0.5 M group. Increased expression of PTGS2, HAS2, and the leptin receptor long form was observed in granulosa cells from the 0.5 M group. No differences between groups were observed for the other transcripts (early growth response factor-1, estrogen receptor-alpha, LH and FSH receptors, gremlin 1, pentraxin 3, KIT ligand, glucose transporters 1, 3, and 8, IGF1, IGF1 receptor, leptin receptor, and tumor necrosis factor-stimulated gene 6). Expression of leptin and sodium/glucose cotransporter 1 was not detected in both groups. The present data indicate that pre-mating nutrition is associated with alteration in the mRNA content in oocytes and surrounding follicle cells in ewes, which may account for the reduced reproductive performance typical of ewes that are fed a restricted ration for a short period of time before mating.

Parthenotes as a source of embryonic stem cells

The derivation and study of human embryonic stem cell lines, despite their potential therapeutic usefulness, raise considerable ethical, religious, legal and political concerns because it inevitably leads to the destruction of viable embryos. In an attempt to bridge the division between ethical questions and potential scientific and medical benefits, considerable efforts have been devoted to the search for alternative sources of pluripotent cell lines. In this review we discuss the use of artificial parthenogenesis as a way to create entities, called parthenotes, that may represent an alternative ethical source for pluripotent cell lines. We describe the biological differences between parthenotes and embryos, in order to provide a rationale for the discussion on whether their use can be acceptable as a source of stem cells. We present data derived from animal models on the extent parthenogenetic stem cells are similar to biparental cell lines and discuss these aspects in the context of their extension to the human species. Finally, we present experiments recently carried out in our laboratory that allowed us to generate human parthenotes through artificial activation of human oocytes and to use them as a source for the derivation of parthenogenetic pluripotent cell lines.

Association between human oocyte developmental competence and expression levels of some cumulus genes

At present, oocyte selection is mainly based upon morphological criteria but it is generally acknowledged that its reliability requires further improvement. The aim of this study was to determine whether transcript levels in cumulus cells can provide a useful marker of oocyte developmental competence in vitro. A retrospective study was performed on cumulus cells isolated from 90 oocytes retrieved from 45 patients. Upon fertilization, 35 oocytes originated good-quality embryos and 36 developed into poor-quality embryos, whereas 19 failed to be fertilized. Semi-quantitative measurement of hyaluronic acid synthase 2 (HAS2), gremlin1 (GREM1), and pentraxin 3 (PTX3) mRNAs was performed and data for all genes were obtained from all the samples. Cumulus cells isolated from oocytes that originated high-quality embryos on day 3 of culture had HAS2 and GREM1 transcript levels higher than those detected in cells from oocytes that did not fertilize or developed into poor-quality embryos. No differences were observed in PTX3 levels. Results indicate that the measurement of HAS2 and GREM1 levels in cumulus cells would reliably complement the morphological evaluation providing a useful tool for selecting oocytes with greater chances to be fertilized and develop in vitro.

Porcine embryonic stem cells: Facts, challenges and hopes

Embryonic stem cells (ESCs) represent a promising tool for cell therapy, regenerative medicine and tissue repair. At the same time they constitute an invaluable model for basic investigations in developmental biology, nuclear reprogramming and differentiation process. ESCs are very unique due to their unlimited self-renewal ability and high plasticity that allow them to differentiate into all embryonic tissues. However, these properties have been so far only demonstrated in the mouse and, to a lesser extent, in man. Assessment of ESC capabilities in species different from the mouse is an ongoing topic of interest and is crucial in view of their potential use as experimental models in pre-clinical applications. The mouse model is not adequate when long-term effects of cell replacement need to be evaluated. The pig has been considered for a long time among the best models for pre-clinical development of therapeutic approaches and represents an innovative model due to its morphological and functional affinity with man; therefore, pig ESCs are attracting renewed interest. However, a number of open questions need to be addressed since no validated protocols for the derivation and maintenance of pig ESCs have yet been established. In the present paper data from the literature will be presented together with experimental evidence recently obtained in our laboratory. We will discuss aspects related to the timing of isolation, the initiation of primary cultures, the use of different culture conditions and cytokines. The identification of pluripotency-related molecular markers in the pig will also be examined. Finally, the ability to respond to specifically formulated medium with spontaneous as well as induced differentiation will be assessed.

Aroclor-1254 affects mRNA polyadenylation, translational activation, cell morphology, and DNA integrity of rat primary prostate cells

Environmental xenobiotics have been shown to act as endocrine disruptors and to be implicated in increased cancer susceptibility. In particular, there is a significant concern regarding the impact of these contaminants on prostate cancer development and progression. However, the mechanisms with which these contaminants exert their detrimental effects are yet unclear and need to be further elucidated. In the present study, we investigated the effects of Aroclor-1254, a mixture of more than 60 environmental pollutants belonging to the polychlorinated biphenyl family, on rat prostate primary cultures. The results obtained after 24-h exposure indicated the ability of this contaminant mixture to influence mRNA stability and length of the 3'-end poly(A)tail of Connexin-32, Connexin-43, and heat shock protein-70. Consistent with this observation, immunostaining experiments demonstrated the altered availability of the encoded proteins. We also focused our attention on possible effects of Aroclor-1254 on cell morphology and could detect ultrastructural changes with gap junction disruption, fusion of single cells into clusters, and different aspects of apoptosis that became evident when exposure to Aroclor-1254 was extended to 72 h. The effects on the nuclear compartment were confirmed by the results obtained with Comet assay that showed DNA decompression and double-strand breaks already after 24-h exposure. Taken together, these findings show a detrimental effect of Aroclor 1254 on rat prostate cells and indicate a possible association between exposure to polychlorinated biphenyl mixture and induction of transformation process in prostate cells.

Temporal and spatial control of gene expression in early embryos of farm animals

A gradual transition from oocyte-derived mRNA and proteins to full embryonic transcription characterises early embryonic development. Messenger RNAs and proteins of maternal origin are accumulated into the oocyte throughout its growth inthe ovary. Upon fertilisation, sev eral mechanisms ar e activated that controlthe appropriate use of such material and prepare for the synthesis of new products. The present review will describe some of the mechanisms active in early embryos of domestic species. Data will be presented on the control of gene expression by the 3' untranslated regions and their interaction with specialised sequences at the 5' cap end. The process of RNA sorting and localisation, initially described in different cell types and in oocytes of lower species, will also be discussed, particularly in relation to its possible role in regulating early pig development. Finally, specific genes involved in the activation of cattle embryonic transcription will be described. This brief overview will provide some suggestions on how these different mechanisms may be integrated and cooperate to ensure the correct initiation of embryonic development.

Cytoplasmic remodelling and the acquisition of developmental competence in pig oocytes

The progression of oocyte meiosis is accompanied by major changes in the ooplasm that play a key role in the completion of a coordinate nuclear and cytoplasmic maturation. We review evidence from the literature and present data obtained in our laboratory on different aspects of pig oocyte cytoplasm compartmentalization during maturation and early embryo development. In particular, we will discuss the changes in adenosine triphosphate (ATP) concentration and distribution taking place during the maturation process and their possible significance for oocyte developmental competence. We describe two important aspects of cytoplasmic streaming: mitochondrial distribution patterns in oocytes and early embryos and the complex rearrangements of cytoplasmic microtubule networks, while discussing their possible correlations with ooplasm compartmentalization. Recent evidence indicates that the cytoskeleton is used to shuttle not only organelles but also mRNAs to specific sites within the oocyte cytoplasm. Localization is driven by specific molecular motors belonging to the kinesin superfamily and requires the involvement of the RNA targeting molecule Staufen. We present recent experimental evidence, obtained in our laboratory, on the pig orthologues for kinesin KIF5B and Staufen, describe their expression patterns and discuss their possible role in oocyte maturation.

In vitro development of human oocytes after parthenogenetic activation or intracytoplasmic sperm injection

OBJECTIVE

To compare directly in vitro developmental competence between parthenogenetically activated and intracytoplasmic sperm injection (ICSI)-fertilized oocytes.

DESIGN

For each patient, three metaphase II oocytes were randomized to the ICSI procedure, while n-3 were allocated to parthenogenetic activation.

SETTING

University hospital infertility unit.

PATIENTS

Thirty-eight patients, aged 35.2 +/- 3.3 years (mean +/- SD) selected for ICSI.

INTERVENTIONS

After 1 hour from denudation, oocytes were either fertilized by ICSI (n = 114) or chemically activated (n = 104). Fertilized and activated oocytes were cultured for up to 3 and 5 days, respectively.

MAIN OUTCOME MEASURES

Development rate, cell number, and morphological grade during culture.

RESULTS

The two groups showed no significant differences between rates of fertilization and parthenogenetic activation, development, and blastomere number on days 2 and 3 of culture. However, parthenotes showed a lower morphological grade, and a significantly lower proportion went on cleaving to day 3, when only activated rather than total numbers of oocytes were considered. On day 5 after activation, nine oocytes (8.6%) reached the blastocyst stage, representing 12.9% of parthenotes.

CONCLUSIONS

Since most parameters examined in this study were similar between activated and fertilized oocytes, parthenogenetic activation may be a useful tool for the preclinical evaluation of experimental procedures.

Derivation and characterization of pluripotent cell lines from pig embryos of different origins

Embryonic stem cells (ESCs) hold great promise for therapeutic use and represent a unique tool for investigating the process of self-renewal and differentiation. The properties that make ESCs unique are their capacity of unlimited self-renewal coupled with the property of re-entering the developmental process if returned inside a blastocyst. Such plasticity enable ESCs to form all embryonic tissues including germ cells. However, these remarkable properties, at present, have been demonstrated only for mouse ESCs even if cells with somehow more limited capacities have been derived in many different species including humans. The isolation of pluripotent embryonic cells lines from human embryos marked a crucial change of perspective in evaluating the properties defining an embryonic stem cell lines moving the focus from the generation of a germ-line chimera, obviously not feasible nor desirable in human, to the capacity of these cells to differentiate both in vivo and in vitro in fully mature and functional cell types of all kinds. Therefore, ESCs properties in species different from the mouse are being reassessed and re-evaluated, in view of their potential use as experimental models for the development of clinical applications. Among the species that may play a useful role in this field, the pig has a long-standing history as a prime animal model for pre-clinical biomedical applications and therefore, pig ESCs are attracting renewed interest. In this review, we will summarize the current knowledge on this topic and will contrast the relatively limited data available in this species with the much larger wealth of information available for mouse and human ESCs, in an attempt to assess whether or not pig ESCs can actually become a useful tool in the fast growing field of cell therapy.

Cellular and molecular mechanisms mediating the effect of polychlorinated biphenyls on oocyte in vitro maturation

Cellular and molecular mechanisms mediating the effect of polychlorinated biphenyls on oocyte in vitro maturation: Polychlorinated biphenyls (PCBs) are stable, lipophilic compounds that accumulate in the environment and in the food chain. Recent studies provide evidence that exposure to PCBs can cause reproductive problems. PCBs have been identified in the ovarian follicle of women and other mammals and many data in the literature clearly indicate that both follicles and oocytes are particularly susceptible to these pollutants. In the present review we describe the multifaceted effects of PCBs on mammalian oocyte maturation in detail. Published studies clearly indicate that PCB congeners, both singly or as complex mixtures, disrupt mammalian oocyte maturation and subsequent embryo development. Specifically, data point out to the ability of PCBs to interfere with the organization of the microtubules cytoplasmic network resulting in an altered compartmentalization of the ooplasm. Furthermore, a critical role of cumulus cells in mediating PCB ovotoxicity has been observed, most likely related to a disregulation in intracellular communication between the germinal and the somatic compartment. Finally, since coplanar PCBs, induce gene expression via a ligand-dependent transactivating factor, the aryl hydrocarbon receptor, this signalling pathway is also reviewed with respect to understanding the toxic mechanisms of these compounds.

Efficiency of equilibrium cooling and vitrification procedures for the cryopreservation of ovarian tissue: comparative analysis between human and animal models

OBJECTIVE

To compare the efficiency of equilibrium cooling and vitrification for cryopreservation of human ovarian tissue and to determine the best experimental model for developing new protocols.

DESIGN

Experimental prospective study.

SETTING

An academic research environment.

PATIENT(S) AND ANIMAL(S)

Human ovarian biopsy specimens were obtained from three women undergoing operative laparoscopy for ovarian cyst enucleation. Adult cow and pig ovaries, collected at the abattoir.

INTERVENTION(S)

Ovarian tissue fragments of three individuals for each species were cryopreserved by using two protocols, either for equilibrium cooling or vitrification.

MAIN OUTCOME MEASURE(S)

Comparison between fresh and cryopreserved tissue of primordial, primary, and secondary follicle morphology, graded in three classes.

RESULT(S)

Human and bovine follicles responded in the same way to the two equilibrium cooling protocols, whereas pig tissue was more cryoresistant. Both vitrification protocols caused extensive damage to the tissue of all species. Human tissue showed a response to vitrification that was different from that of both animal species.

CONCLUSION(S)

Bovine is a good animal model for the development of human ovarian tissue cryopreservation protocols by equilibrium cooling procedures. Vitrification is less efficient than equilibrium cooling, and at present, neither bovine nor pig can be considered relevant animal models for human tissue.

Effects of endocrine disrupters on the oocytes and embryos of farm animals

Currently, approximately 60 chemicals have been identified as endocrine disruptors (EDs): exogenous agents that interfere with the synthesis, secretion, transport, metabolism, binding, action, or elimination of natural blood-borne hormones. Farm animals ingest these substances with food and drinking water. Their stability and lipid solubility has led to increased concern that these substances may compromise the reproductive health of both humans and animals. Oocytes are a permanent cell population established before birth which is exposed to environmental stimuli for a period that, in farm animals, can be as long as several years. Oocyte competence is acquired within the ovary during the developmental stages that precede ovulation and its role is critical during the interval between fertilization and the so-called maternal to embryonic transition, when the transcriptional activity of the embryonic genome becomes fully functional. Any perturbation of these delicate process is likely to reduce oocyte developmental competence and, therefore, to cause an arrest of embryonic development at any given stage. A critical analysis of the doses and time of exposure is presented together with a description of the effects of different EDs on farm animal oocytes and early embryonic development. Finally some of the mechanisms mediating EDs effects on the oocytes will be described. In particular the role of arylhydrocarbon receptor, maternal mRNA stability and cytoplasmic remodelling during oocyte maturation will be discussed in some details.

Expression pattern of the maternal factor zygote arrest 1 (Zar1) in bovine tissues, oocytes, and embryos

Zygote arrest 1 (Zar1) is an ovary-specific maternal factor that plays an essential role during the oocyte-to-embryo transition in mouse. In this species, Zar1 expression is strictly limited to the oocyte, the zygote and, at a lower level, the 2-cell embryo. Aim of the present study was to analyze the presence and the expression pattern of the Zar1 ortholog in bovine tissues and embryos. Reverse transcription (RT)-polymerase chain reaction (PCR) analysis was performed in a panel of bovine tissues, in oocytes and pre-implantation in vitro produced embryos. The results demonstrated that a Zar1 ortholog is present in cattle. In the adult, the gene is expressed in ovary, testis, muscle, and myocardium. The gene is also expressed in the oocyte, the zygote, and in all the stages of embryonic development until blastocyst formation. A semi-quantitative RT-PCR analysis revealed that Zar1 levels are constant through in vitro development with the exception of the 4-cell stage, when a significant increase is observed. The exposure of fertilized oocytes to the RNA polymerase II inhibitor alpha-amanitin was able to suppress this Zar1 increase indicating that transcription of this gene occurs at the 4-cell stage. Zar1 is conserved in cattle but has an expression pattern different from the mouse. In particular, Zar1 expression in the adult is not limited to the ovary and in the embryo is expressed well beyond the oocyte to embryo transition. Moreover, the identification of Zar1 transcription at the 4-cell stage represents the first characterization of one of the genes expressed in cattle embryos before the major onset of embryonic transcription.

Cellular and molecular mechanisms regulating oocyte quality and the relevance for farm animal reproductive efficiency

The efficiency of breeding schemes is dependent on the high fecundity of the selected individuals. Reproductive technologies are constantly pushing the physiological limits, but while the male reproductive potential is almost fully exploited, female reproductive physiology is the subject of constant research. Since the number of offspring that a female can bring to term each pregnancy cannot be changed, the ideal approach is to remove the potential offspring at the beginning of development and to transfer them to recipients of lesser genetic value. The earlier the collection takes place, the higher the number of descendants that a female can generate, so that now, the number of available oocytes becomes the limiting factor. This article will describe how detailed studies on oocyte physiology are beginning to unravel the complex sequence that transforms a small primordial follicle into a large ovulatory follicle containing a mature oocyte. Progressively, the limits to oocyte manipulation have been recognised and gradually overcome with adequate hormonal treatments in vivo and with specific media supplementation in vitro. This has led to the development of highly efficient reproductive technologies and the promise of even greater advances in the future. Surprising new findings, such as ovarian stem cells that can replenish the follicle population or long term embryonic stem cell lines that can differentiate into oocytes, are rapidly changing our expectations.

Effects of Endocrine Disruptors on Developmental and Reproductive Functions

Endocrine disruptors (EDs) are exogenous environmental molecules that may affect the synthesis, secretion, transport, metabolism, binding, action, and catabolism of natural hormones in the body. EDs may thus interact with the endocrine system of animals and humans and can exert this effect even when present in minute amounts. EDs have adverse impacts on a number of developmental functions in wildlife and humans. Critical periods of urogenital tract and nervous system development in-utero and during early post-natal life are especially sensitive to hormonal disruption. Furthermore a wide range of hormone-dependent organs (pituitary gland, hypothalamus, reproductive tract) are targets of EDs disrupting effects in adult subjects, possibly resulting in cell transformation and cancer. At present about 60 chemicals have been identified and characterized as EDs and belong to three main groups: (a) synthetic compounds utilized in industry, agriculture and consumer products; (b) synthetic molecules used as pharmaceutical drugs and (c) natural chemicals found in human and animal food (phytoestrogens). In the present review we will give special attention to the family of Polychlorinated biphenyls (also indicated as PCBs) because of their persistence in the environment, ability to concentrate up the food chain, continued detection in environmental matrices, and ability to be stored in the adipose tissue of animals as well as humans. The detrimental effects of these compounds, and of EDs more in general, on health and reproduction will be discussed, presenting experimental data aimed at understanding the molecular mechanisms involved in their action.

Androgen-induced neurite outgrowth is mediated by neuritin in motor neurones

In the brain, the spinal cord motor neurones express the highest levels of the androgen receptor (AR). Experimental data have suggested that neurite outgrowth in these neurones may be regulated by testosterone or its derivative 5alpha-dihydrotestosterone (DHT), formed by the 5alpha-reductase type 2 enzyme. In this study we have produced and characterized a model of immortalized motor neuronal cells expressing the mouse AR (mAR) [neuroblastoma-spinal cord (NSC) 34/mAR] and analysed the role of androgens in motor neurones. Androgens either activated or repressed several genes; one has been identified as the mouse neuritin, a protein responsible for neurite elongation. Real-time PCR analysis has shown that the neuritin gene is expressed in the basal condition in immortalized motor neurones and is selectively up-regulated by androgens in NSC34/mAR cells; the DHT effect is counteracted by the anti-androgen Casodex. Moreover, DHT induced neurite outgrowth in NSC34/mAR, while testosterone was less effective and its action was counteracted by the 5alpha-reductase type 2 enzyme inhibitor finasteride. Finally, the androgenic effect on neurite outgrowth was abolished by silencing neuritin with siRNA. Therefore, the trophic effects of androgens in motor neurones may be explained by the androgenic regulation of neuritin, a protein linked to neurone development, elongation and regeneration.

Role of adenosine triphosphate, active mitochondria, and microtubules in the acquisition of developmental competence of parthenogenetically activated pig oocytes

The purpose of this work was to determine the mechanisms regulating the acquisition of cytoplasmic maturation and embryonic developmental competence in pig oocytes. The presence or the absence of porcine follicular fluid (pff; 25% or 0%) in the maturation medium was used as a means to achieve complete nuclear maturation accompanied or not accompanied by cytoplasmic maturation. ATP content, active mitochondria relocation, and microtubule distribution were analyzed at different times during in vitro maturation (IVM). While nuclear maturation did not differ among the two groups, parthenogenetic embryonic development was significantly higher (41.5%) in the 25% pff group than in the 0% pff group (19.0%) with blastocysts that had a significantly higher number of blastomeres (76.1 +/- 6.3, and 47.2 +/- 6.5, respectively). Oocyte ATP content increased significantly during IVM, but at the end of maturation no significant differences were observed between high- and low-competence oocytes. An extensive relocation of mitochondria to the inner cytoplasm during IVM together with the formation of a well-developed mesh of cytoplasmic microtubules was observed only in the high-competence oocyte group. However, no differences in the formation of microtubules associated with the meiotic spindles were observed between high- and low-competence groups. We conclude that low developmental competence is associated with the lack of a microtubule cytoplasmic network, which prevents correct relocation of mitochondria and is likely to reflect a more generally altered compartmentalization of the ooplasm. This can be independent from the formation of the microtubule machinery required for the completion of chromosome disjunctions and does not affect the overall ATP content.

Exposure of pig oocytes to PCBs during in vitro maturation: effects on developmental competence, cytoplasmic remodelling and communications with cumulus cells

Polychlorinated biphenyls (PCBs) are one of the most persistent and widespread groups of endocrine disrupting compounds in the ecosystem. These substances are present in sewage sludge that is spread in increasing amounts on arable land and pasture as fertilizer, and are ingested by farm animals with food and drinking water. This study investigated the effect of different PCB concentrations on pig oocyte in vitro maturation and developmental competence as well as examined the possible mechanisms involved. A concentration ranging from 0 to 1 mg/mL of Aroclor 1254 (A1254), a pool of more than 60 PCB congeners, was added to the maturation medium, as its composition is considered environmentally relevant. A1254 had no effect on maturation of pig oocytes and on the number of oocytes that cleaved following parthenogenetic activation at any of the doses tested. By contrast, a significant decrease in the number of zygotes that developed to blastocyst stage became evident at a concentration of 10 ng/mL. The number of blastocysts obtained decreased significantly, and in a dose response manner with higher concentrations. Exposure to PCBs altered mitochondria relocation during maturation and this was associated with the lack of a cytoplasmic microtubule network. No effect on mitochondria activity was observed. A1254 exposure also perturbed gap-junction mediated communications between oocytes and cumulus cells. In conclusion, PCB exposure of pig oocytes during in vitro maturation significantly decreased oocyte developmental competence, altered both their cytoplasmic remodelling and the communication with the somatic compartment. These data indicated that accumulation of PCBs in the pig organism may have a detrimental effect on the reproductive efficiency in this species.

The impact of endocrine disruptors on oocyte competence

To date, approximately 60 chemicals have been identified as endocrine disruptors: exogenous agents that interfere with various aspects of natural hormone physiology. The potential reproductive and health hazards of these environmental chemicals have recently generated concern among the scientific community, policy makers and general public. The present review presents and discusses the available evidence that environmental chemicals are causing ovarian toxicity in various species, with particular attention to farm animals. The impact of chronic exposure to endocrine disruptors via food and drinking water cannot be neglected when studying fertility problems in these species. This review focuses attention on the superfamily of organochlorine chemicals, persistent organic pollutants (POPs), because of their persistence in the environment, ability to concentrate up the food chain, continued detection in environmental matrices and ability to be stored in the adipose tissue of animals and humans. Published data clearly indicate that POPs disrupt mammalian oocyte maturation and follicle physiology in every species studied so far, including farm animals. However, as most of the data available still derive from experiments performed on laboratory species or in vitro models, great care should be taken when extrapolations to other species or environmental situations are attempted.

Evolution of mRNA polyadenylation between oocyte maturation and first embryonic cleavage in cattle and its relation with developmental competence

In this study we analyzed the pattern of polyadenylation changes that takes place between the resumption of meiosis and the first cleavage of bovine oocytes. Moreover, we investigated whether the delayed occurrence of the first cleavage division, which characterizes embryos of low developmental competence, is accompanied by an altered polyadenylation pattern of individual transcripts. We determined the polyadenylation status of a group of genes that characterize physiological processes, involved in early differentiation (Oct-4), compaction, and cavitation (beta-actin, plakophilin, connexin-32, connexin-43), energy metabolism (glucose transporter type 1, pyruvate dehydrogenase phosphatase), RNA processing (RNA poly(A) polymerase), and stress (heat shock protein 70). RNA was isolated from pools of 20 oocytes or embryos at the germinal vesicle (GV) stage, at the end of in vitro maturation, at the end of in vitro fertilization, and at the time of the first cleavage. Cleavage was assessed 27, 30, 36, 42 hr post insemination (hpi), and at the latter time the remaining uncleaved oocytes were retained as a group. Between oocyte isolation and first cleavage at 27 hpi (best quality embryos), the poly(A) tail of individual transcripts followed four patterns: no changes (beta-actin, PDP); gradual reduction (Cx-43, Oct-4, Plako); gradual elongation (Cx-32, TPA); reduction followed by elongation (PAP, HSP-70, Glut-1). If the interval between insemination and first cleavage was longer than 27 hpi (progressively lower quality embryos) further changes of polyadenylation were observed, which differed for each gene considered. These data indicated that specific changes in polyadenylation contribute to the modulation of gene expression in bovine embryos at this stage of development. Defective developmental competence is accompanied by abnormal polyadenylation levels of specific maternal mRNAs with synchrony between polyadenylation and cleavage emerging as an apparently important factor.