Ovum factor: a first signal of pregnancy?

Predicting Embryo Presence and Viability

Pregnancy establishment, followed by birth of live offspring, is essential to all mammals. The biological processes leading up to pregnancy establishment, maintenance, and birth are complex and dependent on the coordinated timing of a series of events at the molecular, cellular, and physiological level. The ability to ovulate a competent oocyte, which is capable of undergoing fertilization, is only the initial step in achieving a successful pregnancy. Once fertilization has occurred and early embryonic development is initiated, early pregnancy detection is critical to provide proper prenatal care (humans) or appropriate management (domestic livestock). However, the simple presence of an embryo, early in gestation, does not guarantee the birth of a live offspring. Pregnancy loss (embryonic mortality, spontaneous abortions, etc.) has been well documented in all mammals, especially in humans and domestic livestock species, and is a major cause of reproductive loss. It has been estimated that only about 25-30% of all fertilized oocytes in humans result in birth of a live offspring; however, identifying the embryos that will not survive to parturition has not been an easy task. Therefore, investigators have focused the identification of products in maternal circulation that permit the detection of an embryo and assessment of its well-being. This review will focus on the advances in predicting embryonic presence and viability, in vivo.

Biomarkers of ovulation, endometrial receptivity, fertilisation, implantation and early pregnancy progression

Increasing interest in early preconception and periconception exposures and human developmental outcomes has led to studies that monitor subjects from before conception to gestation, birth and childhood. Monitoring ovulation, endometrial receptivity, fertilisation, implantation and gestation requires the non-invasive collection of biological information and samples, and the measurement of biochemical and biological markers (biomarkers) that are associated with the aforementioned physiological events. This paper describes some of the key features of biomarkers needed for epidemiological studies, identifies some existing and potential biomarkers and available measurement devices, and suggests some directions for identification and development of new biomarkers that might be employed in longitudinal studies involving the analysis of female reproductive function and of embryonic development.

Early pregnancy factor in marsupials

Maternal recognition of pregnancy in marsupials occurs in more subtle ways than it does in eutherians. For instance, unlike in eutherians, the plasma progesterone profiles of pregnant and non-pregnant animals are similar during the luteal phase. It is typically during the brief luteal phase that both gestation and parturition occur in marsupials. Yet histological and physiological changes have been documented between gravid and non-gravid uteri in certain monovular marsupials and between pregnant and non-pregnant animals in polyovular marsupials. Early pregnancy factor (EPF), a 10.8-kDa serum protein known to be homologous to chaperonin 10, is associated with maternal immunosuppression, embryonic development and pregnancy in eutherian mammals. It has been reported in two Australian marsupials: the dasyurid Sminthopsis macroura and the phalangerid Trichosurus vulpecula. This paper documents its occurrence in the New World didelphid Monodelphis domestica. EPF is detectable by rosette inhibition assay in the peripheral circulation of pregnant but not of non-pregnant or pseudopregnant animals. Our work focuses on the embryo–maternal signalling role of EPF during pregnancy. Because progesterone-driven changes are similar in pregnant and non-pregnant marsupials, these animals are an excellent laboratory model in which to investigate the role of EPF in orchestrating the physiological changes necessary to sustain pregnancy.

Early pregnancy factor: an extracellular chaperonin 10 homologue

Early pregnancy factor (EPF) has been identified as a homologue of chaperonin 10 (cpn10) with immunosuppressive and growth factor properties. As a homologue of cpn10, it belongs to the heat shock family of proteins (hsp) but, unlike other members of this family, EPF is detected extracellularly. Early pregnancy factor was first discovered in pregnancy serum by the rosette inhibition test, and the novelty of its discovery was that its presence could diagnose pregnancy within 6-24 h of a fertile mating. As well as being a monitor of the presence of a viable embryo, it is necessary for embryonic survival. In this capacity it acts as both an immunosuppressant and growth factor. Early pregnancy factor is also a product of proliferating primary and neoplastic cells and functions as an autocrine growth factor both in vivo and in vitro. It has a modifying effect on the outcome of experimental autoimmune encephalomyelitis, an animal model of multiple sclerosis. Early pregnancy factor is considered to be one of the major factors involved in the modification of multiple sclerosis observed during pregnancy.

Supplementation effect of early pregnancy factor-positive serum into bovine in vitro fertilization culture medium

PROBLEM

Early pregnancy factor (EPF) has been detected in pregnant bovine serum, and its activity appeared from 24 to 48 hr after insemination. However, in bovine in vitro fertilization (IVF), an EPF-like substance(s) had been detected in the culture medium of fertilized ovum. Therefore, we think that EPF and EPF-like substance(s) are very important materials for the development of the embryo. In this study, we examined the development of the embryo when fertilized bovine ova were cultured with IVF culture medium supplemented with EPF-positive or -negative serum.

METHOD OF STUDY

EPF activity of each serum (fetal calf serum [FCS], calf serum [CS], estrus bovine serum, and pregnant bovine serum) was assessed by the bovine-rosette inhibition test. The sera were supplemented in TCM-199 culture medium, and IVF bovine ova were cultured with the media for 6 or 7 days, respectively. The culture media of each group were evaluated for EPF activity by the bovine-rosette inhibition test 48 hr after IVF. The cleavage rate of each group was calculated at 48 hr, and 6 or 7 days after IVF. The culture medium of cumulus cells was also tested for EPF activity.

RESULTS

Only the pregnant bovine sera were EPF positive. All the culture media 48 hr after IVF became EPF positive. Additionally, the culture medium of cumulus cells did not have EPF activity. There was no significant difference in the cleavage rate of the EPF-positive and -negative sera 48 hr after IVF. However, the cleavage rate of EPF-positive sera tended to be higher than the negative sera. In contrast, the blastocyst development rates of EPF-positive sera were significantly higher than those of the negative sera 6 to 7 days after IVF (P < 0.05).

CONCLUSIONS

The data suggest that an EPF-like substance(s) may be secreted from the in vitro fertilized bovine ovum but not from the cumulus cell, and that the EPF in the pregnant serum may accelerate the development of the bovine embryo in IVF.

Prolactin (PRL) and its receptor: actions, signal transduction pathways and phenotypes observed in PRL receptor knockout mice

PRL is an anterior pituitary hormone that, along with GH and PLs, forms a family of hormones that probably resulted from the duplication of an ancestral gene. The PRLR is also a member of a larger family, known as the cytokine class-1 receptor superfamily, which currently has more than 20 different members. PRLRs or binding sites are widely distributed throughout the body. In fact, it is difficult to find a tissue that does not express any PRLR mRNA or protein. In agreement with this wide distribution of receptors is the fact that now more than 300 separate actions of PRL have been reported in various vertebrates, including effects on water and salt balance, growth and development, endocrinology and metabolism, brain and behavior, reproduction, and immune regulation and protection. Clearly, a large proportion of these actions are directly or indirectly associated with the process of reproduction, including many behavioral effects. PRL is also becoming well known as an important regulator of immune function. A number of disease states, including the growth of different forms of cancer as well as various autoimmune diseases, appear to be related to an overproduction of PRL, which may act in an endocrine, autocrine, or paracrine manner, or via an increased sensitivity to the hormone. The first step in the mechanism of action of PRL is the binding to a cell surface receptor. The ligand binds in a two-step process in which site 1 on PRL binds to one receptor molecule, after which a second receptor molecule binds to site 2 on the hormone, forming a homodimer consisting of one molecule of PRL and two molecules of receptor. The PRLR contains no intrinsic tyrosine kinase cytoplasmic domain but associates with a cytoplasmic tyrosine kinase, JAK2. Dimerization of the receptor induces tyrosine phosphorylation and activation of the JAK kinase followed by phosphorylation of the receptor. Other receptor-associated kinases of the Src family have also been shown to be activated by PRL. One major pathway of signaling involves phosphorylation of cytoplasmic State proteins, which themselves dimerize and translocate to nucleus and bind to specific promoter elements on PRL-responsive genes. In addition, the Ras/Raf/MAP kinase pathway is also activated by PRL and may be involved in the proliferative effects of the hormone. Finally, a number of other potential mediators have been identified, including IRS-1, PI-3 kinase, SHP-2, PLC gamma, PKC, and intracellular Ca2+. The technique of gene targeting in mice has been used to develop the first experimental model in which the effect of the complete absence of any lactogen or PRL-mediated effects can be studied. Heterozygous (+/-) females show almost complete failure to lactate after the first, but not subsequent, pregnancies. Homozygous (-/-) females are infertile due to multiple reproductive abnormalities, including ovulation of premeiotic oocytes, reduced fertilization of oocytes, reduced preimplantation oocyte development, lack of embryo implantation, and the absence of pseudopregnancy. Twenty per cent of the homozygous males showed delayed fertility. Other phenotypes, including effects on the immune system and bone, are currently being examined. It is clear that there are multiple actions associated with PRL. It will be important to correlate known effects with local production of PRL to differentiate classic endocrine from autocrine/paracrine effects. The fact that extrapituitary PRL can, under some circumstances, compensate for pituitary PRL raises the interesting possibility that there may be effects of PRL other than those originally observed in hypophysectomized rats. The PRLR knockout mouse model should be an interesting system by which to look for effects activated only by PRL or other lactogenic hormones. On the other hand, many of the effects reported in this review may be shared with other hormones, cytokines, or growth factors and thus will be more difficult to study. (ABSTRACT TRUNCATED)

Null mutation of the prolactin receptor gene produces multiple reproductive defects in the mouse

Mice carrying a germ-line null mutation of the prolactin receptor gene have been produced by gene targeting in embryonic stem cells. Heterozygous females showed almost complete failure of lactation attributable to greatly reduced mammary gland development after their first, but not subsequent, pregnancies. Homozygous females were sterile owing to a complete failure of embryonic implantation. Moreover, they presented multiple reproductive abnormalities, including irregular cycles, reduced fertilization rates, defective preimplantation embryonic development, and lack of pseudopregnancy. Half of the homozygous males were infertile or showed reduced fertility. This work establishes the prolactin receptor as a key regulator of mammalian reproduction, and provides the first total ablation model to further study the role of the prolactin receptor and its ligands.

Synthesis of early pregnancy factor using red deer (Cervus elaphus) as a delayed implantation model

PURPOSE

This study measured serum early pregnancy factor (EPF) in pregnant red deer (Cervus elaphus) and ascertained whether EPF synthesis is associated with implantation.

METHODS

Serial serum samples were taken from mated hinds up to 42 days postconception and analyzed for EPF activity using the rosette inhibition test. EPF activity was then correlated with calving records and stages of preimplantation development.

RESULTS

EPF was detected in all pregnant animals, with a twin pregnancy giving increased EPF activity. Three animals gave an EPF response following fertilization but failed to continue beyond the preimplantation embryo stage. The increase in EPF synthesis previously associated with implantation in other mammals occurred at the blastocyst stage in red deer.

CONCLUSIONS

EPF synthesis in red deer (Cervus elaphus) is consistent with the preimplantation period, as occurs in other mammals. However, the second phase of the biphasic increase in early pregnancy factor production is associated with blastocyst formation, not implantation.

Early pregnancy factor (EPF) as a marker for detecting subclinical embryonic loss in clomiphene citrate-treated women

PROBLEM

A discrepancy exists between the apparently normal ovulation and the pregnancy rates in women treated with clomiphene citrate (CC). Our previous studies have indicated that immuno-suppressive "early pregnancy factor" (EPF) is a novel marker to detect subclinical embryonic loss in infertile women.

METHOD

In the present study EPF was used as a marker to detect subclinical embryonic loss in women treated with CC with/without gonadotropins. In some of the women treated with CC, conception was assisted by artificial insemination with husband's semen (AIH).

RESULTS

Our results have indicated that fertilization occurred (EPF + ve) in 47.7% (52/109) of women treated with CC with/without gonadotropins; 13.46% (7/52) retained the fetus and continued pregnancy till full term, whereas 78.9% (41/52) did not retain the fetuses. In the group where after stimulation, conception was assisted by AIH, fertilization was observed in 38.24% (26/68), retention in 11.54% (3/26) but subclinical embryonic loss was observed in 80.8% (21/26) cases.

CONCLUSION

Thus, our results have indicated that subclinical embryonic loss may account for some of the discrepancy observed between the apparently normal ovulation and the pregnancy rates in women treated with clomiphene citrate.

Structural changes in the oviductal wall during the passage of unfertilized cumulus-oocyte complexes in mice

BACKGROUND

Little information is available on the structural relationship of cumulus-oocyte complexes and the oviductal wall during the transport of cumulus-oocyte complexes. Then, morphological changes of the oviductal wall during the passage of unfertilized cumulus-oocyte complexes was examined chronologically in ICR mice 25-27 days of age injected with PMSG and hCG.

METHODS

Mice were sacrificed at 12, 14, 16, 18, and 24 hr after the injection of hCG to remove oviducts, and the height of mucosal folds, muscle layers, and epithelial cells were measured in the serial sections stained with hematoxylin-eosin or colloidal iron.

RESULTS

The height of the mucosal fold and muscle layer where cumulus-oocyte complexes were located was less than that of the adjacent portions. At 12-18 hr of hCG injection (about 2-8 hr after ovulation), the ova with surrounding cumulus cells lie free in a wide lumen, and the muscular tissue consists of only 2 or 3 layers of cells, arranged mostly longitudinally. However, a neighboring portion without cumulus-oocyte complexes, where the folds meet in the middle, appreciably restricts the free space in the lumen. After 24 hr of hCG administration, structural changes in the oviductal wall, where cumulus-oocyte complexes were located, were no longer apparent. The number of cumulus cells surrounding the oocyte decreased during the passage through the oviduct. At 12-18 hr after hCG injection, about 140 cells were identified in the largest cross section of a cumulus-oocyte complex, but, after 24 hr of hCG administration (about 14 hr after ovulation), an oocyte was surrounded with only about 25 cells.

CONCLUSIONS

These results indicate that oocyte-cumulus cell complexes influence the structure of the oviductal wall during the passage in the oviduct.

Structural changes in the oviductal wall during passage of unfertilized cumulus-oocyte complexes in mice

BACKGROUND

Little information is available on the structural relationship of cumulus-oocyte complexes and the oviductal wall during the transport of cumulus-oocyte complexes.

METHODS

To this end, morphological changes of the oviductal wall during the passage of unfertilized cumulus-oocyte complexes were examined chronologically in ICR mice 25-27 days of age injected with PMSG and hCG. Mice were sacrificed at 12, 14, 16, 18, and 24 hr after the injection of hCG to remove oviducts, and the height of mucosal folds, muscle layers, and epithelial cells was measured in the serial sections stained with hematoxylineosin or colloidal iron.

RESULTS

The height of the mucosal fold and muscle layer where cumulus-oocyte complexes were located was less than that of the adjacent portions. At 12-18 hr of hCG injection (approximately 2-8 hr after ovulation), the ova with surrounding cumulus cells lie free in a wide lumen, and the muscular tissue consists of only 2 or 3 layers of cells, arranged mostly longitudinally. However, a neighboring portion without cumulus-oocyte complexes, where the folds meet in the middle, appreciably restricts the free space in the lumen. After 24 hr of hCG administration, structural changes in the oviductal wall, where cumulus-oocyte complexes were located, were no longer apparent. The number of cumulus cells surrounding the oocyte decreased during the passage through the oviduct. At 12-18 hr after hCG injection, approximately 140 cells were identified in the largest cross section of a cumulus-oocyte complex, but after 24 hr of hCG administration (approximately 14 hr after ovulation), an oocyte was surrounded with only approximately 25 cells.

CONCLUSIONS

These results indicate that oocyte-cumulus cell complexes influence the structure of the oviductal wall during the passage in the oviduct.

The partially purified pre-implantation suppressor factor may be one of several factors to play a role in successful pregnancy

Embryo-associated immunosuppressor factor (EASF) is detected by its suppressive properties in the concanavalin A (ConA)-induced lymphocyte proliferation assay. EASF was partially purified from human embryo growth media of in vitro fertilized ova (pre-implantation EASF) as three fractions. The aim of the present study was to determine whether the EASF isolated from human embryo growth media is similar to the EASF secreted by the pre-embryo, which has been shown to be associated with successful pregnancy. EASF activity was measured in the purified pre-implantation EASF fractions and in a total of 24 individual embryo growth media obtained from 10 patients undergoing in vitro fertilization and embryo transfer, where 6 patients achieved successful pregnancy and 4 did not. The results show that: (i) all three EASF fractions and the individual embryo growth media from patients who became pregnant were suppressive when added to the early phase of ConA-supplemented cultures; this was not seen with the embryo growth media from patients who failed to become pregnant, suggesting that the purified pre-implantation EASF may be one of several factors responsible for successful pregnancy; and (ii) some embryo growth media, irrespective of the pregnancy outcome of the patient, showed an irreversible immunosuppressive effect on ConA-induced lymphocyte proliferation, whereas none of the purified EASF fractions did; this could be due to the loss of activity during purification.

Human embryonic origin early pregnancy factor before and after implantation

Early pregnancy factor (EPF) is a factor that has been shown to be involved in the maintenance of the fetal allograft in several mammalian species including man. In that capacity it serves as a link between fertilization and immunomodulation. In the present study we have investigated the secretion of EPF by the human conceptus before and after implantation using rosette inhibition antibody concentration (T11 monoclonal antibody). In isolated trophoblastic cells at gestational week 7-9 there was a significant secretion of EPF. For the first 8 days in culture, secretion was maximal; later, however, at days 13 and 21 these levels declined. Further the EPF content of human embryonal extracts was examined. In various organs, spinal cord, liver, and kidney, significant EPF activity was detected. In women undergoing in vitro fertilization/embryo transfer, a total of 52 preimplantational embryos were cultured for 36 hours. No significant EPF activity was detected in the surrounding media. Two of the 11 patients studied became pregnant during the same cycle after embryo transfer. In conclusion, the preimplantational origin of EPF is maternal, while that of the post-implantational embryo is of embryonal origin.

Purified human early pregnancy factor from preimplantation embryo possesses immunosuppresive properties

This study was undertaken to determine whether early pregnancy factor secreted by preimplantation embryos has immunosuppressive properties. Human early pregnancy factor was purified from embryo growth media of in vitro fertilized ova with ion-exchange and gel filtration chromatography. During each step of purification the fractions were tested for (1) early pregnancy factor activity with the rosette inhibition assay, (2) immunosuppressive properties with a concanavalin A-stimulated lymphocyte proliferation assay, and (3) purity by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Results indicate that (1) human early pregnancy factor has a basic molecular weight of 14 kd, (2) early pregnancy factor has immunosuppressive activity, (3) polymers of early pregnancy factor also appear to be present in the embryo growth media, and (4) immunosuppressive factors other than early pregnancy factor are also secreted by preimplantation human embryos. Early pregnancy factor and other factor(s) produced by the preimplantation embryo may play a role in suppressing maternal cellular immune responses, thereby preventing maternal rejection of the embryo.

Platelet activating factor-induced early pregnancy factor activity from the perfused rabbit ovary and oviduct

Early pregnancy factor, a glycoprotein, and platelet activating factor, a phospholipid, are early signals of pregnancy appearing during the preimplantation period. The aim of this study was to determine if the administration of platelet activating factor to rabbits would stimulate the production of early pregnancy factor and, if so, to ascertain the organs responsible. Early pregnancy factor was assayed after the administration of synthetic platelet activating factor to intact rabbits, rabbits that had undergone bilateral salpingo-oophorectomy, and isolated in vitro perfused rabbit ovary and/or oviduct. Although serum early pregnancy factor activity was detectable 30 minutes after platelet activating factor injection in intact rabbits, no activity was found in rabbits whose ovaries and oviducts had been removed. Perfusate early pregnancy factor activity was detectable only in the presence of both ovary and oviduct, and was first evident 120 minutes after platelet activating factor exposure. However, combined samples of perfusates from the ovary alone and oviduct alone expressed positive early pregnancy factor activity. Furthermore, the addition of platelet activating factor to either single or combined perfusates did not increase early pregnancy factor activity. Our data imply that platelet activating factor induces the production of ovary and oviduct early pregnancy factor components independently.

An evaluation of peripheral blood platelet enumeration as a monitor of fertilization and early pregnancy

This paper reports our data that confirm the existence of early pregnancy-associated thrombocytopenia (EPAT) in the mouse and illustrate that the phenomenon is independent of age, parity, and strain differences. This paper also provides evidence that the EPAT phenomenon is induced by a soluble factor (EPAT-factor) released by the fertilized ovum. EPAT-factor was produced in vitro by mouse embryos from the 1-cell stage to the expanded blastocyst stage. The human study involved a "blind" analysis of serum samples, collected from in vitro fertilization-treated patients, for the presence of thrombocytopenic activity. Results suggest that measurement of this thrombocytopenic activity might be useful as an index of embryo viability and might be clinically applicable for the monitoring of implantation success in in vitro fertilization programs.

Isolation and partial characterization of early pregnancy factor (EPF) from human pregnancy serum

The isolation and partial characterization of an immunosuppressive early pregnancy factor (EPF) present in the serum of pregnant women, between 3 and 8 weeks of gestation, is described. EPF was purified using ion-exchange chromatography, affinity chromatography and HPLC gel permeation techniques. A homogeneous, active fraction containing a single polypeptide of Mr 21,000 was obtained. This 21 kDa polypeptide appears to represent the major form of rosette-inhibiting active material present in maternal serum during early human gestation.

In search of early pregnancy factor: characterisation of active polypeptides isolated from pregnant ewes' sera

Further biochemical characterisations of the 20 kd and 67 kd EPF active polypeptides from pregnant ewes' sera are described. Both polypeptides are shown to possess compact, disulphide linked domains which are almost totally resistant to proteolytic attack without prior reduction. In contrast to previous reports on the influence of ammonium sulphate on the expression of EPF activity, neither the biochemical nor the activity characteristics of either polypeptide is changed by ammonium sulphate fractionation. In addition, direct comparative studies have been performed which clearly distinguish the EPF active polypeptides from the known ovine hormones, prolactin, placental lactogen and growth hormone.

Modified rosette inhibition test with mouse lymphocytes for detection of early pregnancy factor in human pregnancy serum

The rosette inhibition test has been modified so that early pregnancy factor (EPF) in human pregnancy serum can be detected with mouse lymphocytes. Interference with the assay, which would result from incubation of lymphocytes with heterologous serum proteins, is prevented by the introduction of an ion exchange chromatography step. This provides a simple and rapid method for separating EPF from interfering serum proteins. Human pregnancy and non-pregnancy sera were assayed for EPF with human lymphocytes and results compared with those obtained with DEAE-Sephacel fractions of the same sera tested with mouse lymphocytes. The 2 systems showed good agreement but the mouse assay gave greater differentiation between positive and negative results. When monoclonal anti-T cell antibodies, Hu Ly-m1 and anti-Ly-1.1, were substituted for anti-lymphocyte sera in the human and mouse assay systems respectively, similar results were obtained. The mouse assay system has several advantages over the human assay, including stability of the anti-mouse lymphocyte serum and the ready availability of mouse lymphocytes. Moreover the modified method may be applied not only to the assay of human EPF, but also to the assay of EPF from other species. This would be of value if several species were being studied in 1 laboratory, or if sufficient quantities of lymphocytes from a particular species were not available.

Detection of an early pregnancy factor-like substance in sera of patients with testicular germ cell tumors

Early pregnancy factor (EPF) is produced by both maternal and fetal tissue1,2 and has been detected previously only during pregnancy.3,4 The present report describes the detection of EPF, or an EPF-like substance (tEPF), in serum from patients with germ cell tumors of the testis. tEPF, or its free components, tEPF-A and tEPF-B, were detected in all 11 patients with nonseminomatous tumors and in 5 of 10 patients with seminoma. It was not detected in serum from healthy male controls nor in patients with non-germ cell tumors or benign testicular disease. It is suggested that tEPF may be an additional serum marker for germ cell tumors and may expand the group already detectable by such markers.

Detection of fetal wastage

Production of the pregnancy-specific protein early pregnancy factor (EPF) was monitored by the rosette inhibition test in a group of 13 nulliparous women. EPF could be detected in serum within 48 hours of fertilization; of 28 cycles in which intercourse took place at the time of ovulation, EPF was detected in 18. However, EPF production continued for more than 14 days in only four cases. Successful pregnancy was maintained in two of these while in the other two, disappearance of EPF preceded miscarriage. In the remaining 14 cases, EPF disappeared from the serum before the onset of menstruation. A high incidence of early embryonic loss is suggested.