Monkey Placenta Research Articles

Similarities and differences in placental development between humans and cynomolgus monkeys.

The placenta is an extraembryonic organ, which is essential to maintain a normal pregnancy. However, placental development in humans is poorly understood because of technical and ethical reasons. We analyzed the anatomical localization of each trophoblastic subtype in the cynomolgus monkey placenta by immunohistochemistry in the early second trimester. Histological differences among the mouse, cynomolgus monkey, and human placenta were compared. The PubMed database was used to search for studies on placentation in rodents and primates. The anatomical structures and subtypes of the placenta in cynomolgus monkeys are highly similar to those in humans, with the exception of fewer interstitial extravillous trophoblasts in cynomolgus monkeys. The cynomolgus monkey appears to be a good animal model to investigate human placentation.

Analysis of developmental imprinting dynamics in primates using SNP-free methods to identify imprinting defects in cloned placenta.

Our knowledge of genomic imprinting in primates is lagging behind that of mice largely because of the difficulties of allelic analyses in outbred animals. To understand imprinting dynamics in primates, we profiledtranscriptomes, DNA methylomes, and H3K27me3 in uniparental monkey embryos. We further developed single-nucleotide-polymorphism (SNP)-free methods, TARSII and CARSII, to identify germline differentially methylated regions (DMRs) in somatic tissues. Our comprehensive analyses showed that allelicDNA methylation, but not H3K27me3, is a major mark that correlates with paternal-biasedly expressed genes (PEGs) in uniparental monkey embryos. Interestingly, primate germline DMRs are different from PEG-associated DMRs in early embryos and are enriched in placenta. Strikingly, most placenta-specificgermline DMRs are lost in placenta of cloned monkeys. Collectively, our study establishes SNP-free germline DMR identification methods, defines developmental imprinting dynamics in primates, and demonstrates imprinting defects in cloned monkey placenta, which provides important clues for improving primate cloning.

Сравнительная характеристика аминокислотного состава и активности ферментов аминокислотного обмена в гемохориальной плаценте разных видов животных и человека

The amino acid composition and activity of the enzymes of the amino acid metabolism of placenta were studied. The objects of the study were guinea pigs (Cavia porcellus) and rhesus macaques (Macaca mulatta), which have a hemochoric placenta type, similar to humans. The study also included women with uncomplicated pregnancy and delivery on time (39-40 weeks). It was found that in the all tissues studied, the fetal part of the placenta is characterized by the highest content of free and bound amino acids. In the fetal part of the placenta, the maximal activity of amino acid metabolism enzymes (aminotransferases, deaminases, amino synthetases) was also found. Common to the placenta of guinea pigs, monkeys and humans is also a high level of dicarboxylic amino acids and glutamine. Along with the common features in the amino acid metabolism of the placenta of different species of animals and humans, some differences were revealed due to the evolutionary features of the development of the organ, the specifics of the existing maternal-fetal relationships. Interspecies differences of the same parts of the placenta relate to individual amino acids, the majority of which in the placenta of rodents exceeds similar indicators in primates. Between the placentas of humans and monkeys, the differences in the studied biochemical parameters are less pronounced. Another difference between guinea pig placenta and human and monkey placenta is the unequal non-covalent binding of amino acids to biopolymers, which modifies the state of the acceptor groups of proteins. Similar tissues of the afterbirth of different species of animals and humans differ in the activity of amino acid metabolism enzymes. There is a close correlation between the content of free amino acids and indicators of enzyme activity, showing their important role in the formation of the placental amino acid fund.

Self-contained image mapping of placental vasculature in 3D ultrasound-guided fetoscopy.

Surgical navigation technology directed at fetoscopic procedures is relatively underdeveloped compared with other forms of endoscopy. The narrow fetoscopic field of views and the vast vascular network on the placenta make examination and photocoagulation treatment of twin-to-twin transfusion syndrome challenging. Though ultrasonography is used for intraoperative guidance, its navigational ability is not fully exploited. This work aims to integrate 3D ultrasound imaging and endoscopic vision seamlessly for placental vasculature mapping through a self-contained framework without external navigational devices. This is achieved through development, integration, and experimentation of novel navigational modules. Firstly, a framework design that addresses the current limitations based on identified gaps is conceptualized. Secondly, integration of navigational modules including (1) ultrasound-based localization, (2) image alignment, and (3) vision-based tracking to update the scene texture map is implemented. This updated texture map is projected to an ultrasound-constructed 3D model for photorealistic texturing of the 3D scene creating a panoramic view of the moving fetoscope. In addition, a collaborative scheme for the integration of the modular workflow system is proposed to schedule updates in a systematic fashion. Finally, experiments are carried out to evaluate each modular variation and an integrated collaborative scheme of the framework. The modules and the collaborative scheme are evaluated through a series of phantom experiments with controlled trajectories for repeatability. The collaborative framework demonstrated the best accuracy (5.2% RMS error) compared with all the three single-module variations during the experiment. Validation on an ex vivo monkey placenta shows visual continuity of the freehand fetoscopic panorama. The proposed developed collaborative framework and the evaluation study of the framework variations provide analytical insights for effective integration of ultrasonography and endoscopy. This contributes to the development of navigation techniques in fetoscopic procedures and can potentially be extended to other applications in intraoperative imaging.

Towards scene adaptive image correspondence for placental vasculature mosaic in computer assisted fetoscopic procedures.

Visualization of the vast placental vasculature is crucial in fetoscopic laser photocoagulation for twin-to-twin transfusion syndrome treatment. However, vasculature mosaic is challenging due to the fluctuating imaging conditions during fetoscopic surgery. A scene adaptive feature-based approach for image correspondence in free-hand endoscopic placental video is proposed. It contributes towards existing techniques by introducing a failure detection method based on statistical attributes of the feature distribution, and an updating mechanism that self-tunes parameters to recover from registration failures. Validations on endoscopic image sequences of a phantom and a monkey placenta are carried out to demonstrate mismatch recovery. In two 100-frame sequences, automatic self-tuned results improved by 8% compared with manual experience-based tuning and a slight 2.5% deterioration against exhaustive tuning (gold standard). This scene-adaptive image correspondence approach, which is not restricted to a set of generalized parameters, is suitable for applications associated with dynamically changing imaging conditions. Copyright © 2015 John Wiley & Sons, Ltd.

Vision-based endoscope tracking for 3D ultrasound image-guided surgical navigation

This work introduces a self-contained framework for endoscopic camera tracking by combining 3D ultrasonography with endoscopy. The approach can be readily incorporated into surgical workflows without installing external tracking devices. By fusing the ultrasound-constructed scene geometry with endoscopic vision, this integrated approach addresses issues related to initialization, scale ambiguity, and interest point inadequacy that may be faced by conventional vision-based approaches when applied to fetoscopic procedures. Vision-based pose estimations were demonstrated by phantom and ex vivo monkey placenta imaging. The potential contribution of this method may extend beyond fetoscopic procedures to include general augmented reality applications in minimally invasive procedures.

Comparison of fresh to fixed weights of the vervet monkey (Chlorocebus sabaeus) placenta and its relation to gestational age

Focus on the placenta as an agent of fetal development and offspring health outcomes is growing. Primate research facilities or zoos may collect and fix placental tissue for long-term storage, but little is known about the effects of formalin fixation on the non-human primate placenta. We obtained 48 vervet monkey placentas from the St. Kitts Biomedical Research Foundation. We investigated via correlation coefficients and ANOVAs the effects of gestational age and original fresh weight on weight change due to fixation. We also used linear regression models to determine whether fixed tissue weight was predictive of fresh weight and gestational age. Although the vervet monkey placenta is described as bidiscoid, 14.6% of the placentas in this sample were fused into a single mass. A decrease in weight was the most common response to formalin fixation, with the greatest degree of loss experienced by the heaviest placentas (ANOVA, F=5.99, P=0.005). Gestational age was unrelated to weight change. Those placentas that increased in weight had the lowest fresh weights. Fixed weights significantly predicted both fresh weight and gestational age (r(2) =0.78, P<0.00001; r(2) =0.76, P<0.00001, respectively). This paper adds to a sparse literature on the vervet monkey placenta. That fixed placentas are excellent predictors of both fresh weight and gestational age suggests that banked tissue may be a valuable resource for reconstructing aspects of individual life history, although caution must be exercised given the variability of weight change as a function of original placental size.

Full-length cDNA sequences from Rhesus monkey placenta tissue: analysis and utility for comparative mapping

BackgroundRhesus monkeys (Macaca mulatta) are widely-used as experimental animals in biomedical research and are closely related to other laboratory macaques, such as cynomolgus monkeys (Macaca fascicularis), and to humans, sharing a last common ancestor from about 25 million years ago. Although rhesus monkeys have been studied extensively under field and laboratory conditions, research has been limited by the lack of genetic resources. The present study generated placenta full-length cDNA libraries, characterized the resulting expressed sequence tags, and described their utility for comparative mapping with human RefSeq mRNA transcripts.ResultsFrom rhesus monkey placenta full-length cDNA libraries, 2000 full-length cDNA sequences were determined and 1835 rhesus placenta cDNA sequences longer than 100 bp were collected. These sequences were annotated based on homology to human genes. Homology search against human RefSeq mRNAs revealed that our collection included the sequences of 1462 putative rhesus monkey genes. Moreover, we identified 207 genes containing exon alterations in the coding region and the untranslated region of rhesus monkey transcripts, despite the highly conserved structure of the coding regions. Approximately 10% (187) of all full-length cDNA sequences did not represent any public human RefSeq mRNAs. Intriguingly, two rhesus monkey specific exons derived from the transposable elements of AluYRa2 (SINE family) and MER11B (LTR family) were also identified.ConclusionThe 1835 rhesus monkey placenta full-length cDNA sequences described here could expand genomic resources and information of rhesus monkeys. This increased genomic information will greatly contribute to the development of evolutionary biology and biomedical research.

The immunohistochemical localization of new membrane-associated placental tissue proteins (MP2 A, B, C, D, and E) in human and cynomolgus monkey placentae.

New membrane-associated placental tissue proteins (MP2 A, B, C, D, and E) were investigated by avidin-biotin immunoperoxidase technique in the human and cynomolgus monkey placentae, decidua and umbilical cords. In human early placentae, MP2 A, B, C, and E were localized mainly in the membrane of villous syncytiotrophoblasts and cytotrophoblasts. Histiocytes in the villous stroma were positive for MP2 A, B, D, and E. In human term placentae, obvious positive staining for MP2 A, B, C, and E was observed in the membrane of villous syncytiotrophoblasts, in the amniotic epithelium, and in the umbilical cord sheath. Histiocytes in the villous stroma were positive for MP2 A, B, C, E, and especially for MP2 D. Importantly, MP2 A, C, and E were positive in polymorphonuclear neutrophils, since most of these common antigens are also carcinoma-associated, suggesting clinical usage of MP2 proteins as a new tumor marker. In the cynomolgus monkey placentae, similar immuno-staining results were obtained. The monkey can thus serve as a experimental model for the investigation of the placental proteins.

ICG fluorescence endoscope for visualization of the placental vascular network

Intrauterine laser photocoagulation for twin-twin transfusion syndrome (TTTS) needs accurate in-situ recognition of placental vascular anastomosis. Because the conventional procedure is highly dependent upon the operators’ skill and experience, we developed a new way to visualize the placental vascular network by a rigid-type fluorescence endoscope coupled with intravenous administration of Indocyanine green (ICG). The feasibility of the fluorescence endoscope was examined with monkey placentas and pregnant rats. The ICG fluorescence endoscope can visualize the placental vascular network in detail even in the presence of turbid amniotic fluid. Thus, this method is potentially useful for in-situ definition of the placental vascular anastomoses during the treatment for TTTS. In addition, our rigid-type fluorescence endoscope will also be a useful tool for lymph node dissection using ICG by endoscopic surgery.

Non-classical MHC-E (Mamu-E) Expression in the Rhesus Monkey Placenta

The aim of this study was to characterize the expression of the rhesus HLA-E ortholog Mamu-E, particularly at the maternal–fetal interface. Mamu-E expression was confirmed by locus-specific RT-PCR in the placenta as well as in peripheral blood mononuclear cells (PBMC) and other organs. We evaluated the utility of antibodies recognizing HLA-E (MEM-E/06 against native HLA-E, MEM-E/02 against denatured HLA-E) to detect Mamu-E by flow cytometry/immunofluorescence, Western blot, and immunohistochemistry (IHC). Western blot analysis of cells and selected transfectants confirmed the recognition of Mamu-E but not Mamu-AG by antibodies MEM-E/06 and HC10 but not MEM-E/02. Immunohistochemical staining of frozen sections of rhesus placenta with the MEM-E/06 antibody demonstrated expression in most populations of rhesus monkey trophoblast cells, including villous cytotrophoblasts (strong positive staining), apical membrane of syncytiotrophoblasts (light to moderate staining) and extravillous cytotrophoblasts (moderate to strong staining, especially endovascular trophoblasts in early pregnancy). Expression was not trophoblast cell-specific, especially at term, when endothelial cells in both the chorionic plate and placental villi showed strong staining for Mamu-E. Staining of rhesus extravillous trophoblast cells suggested the co-expression of Mamu-E and Mamu-AG (the rhesus HLA-G homolog) on these cells. MEM-E/06 was shown also to react with differentiating rhesus placental syncytiotrophoblasts in primary culture, detecting intracellular and weak surface expression of Mamu-E. We conclude that the gestation-dependent co-expression of Mamu-E with Mamu-AG in villous and extravillous trophoblast cells suggests important and perhaps complementary but distinct roles of these two non-classical MHC class I loci in pregnancy at the maternal–fetal interface. In addition, the MEM-E/06 antibody will be useful for the detection of Mamu-E at the maternal–fetal interface in the rhesus monkey.

Trophoblast invasion and local immune response in the rhesus monkey placenta after anti-Mamu-AG passive immunization

Trophoblast invasion and local immune response in the rhesus monkey placenta after anti-Mamu-AG passive immunization

Uptake and Decarboxylation of l-3,4-Dihydroxyphenylalanine in Cultured Monkey Placenta Amniotic Epithelial Cells

In this study we tested the ability of monkey amniotic epithelial cells (MAEC) to take up and decarboxylate l-3,4-dihydroxyphenylalanine ( l-DOPA) by incubating the cells in buffer containing l-DOPA under different experimental conditions followed by assaying cellular dopamine (DA) content using high performance liquid chromatography with electrochemical detection. Cellular contents of DA were significantly increased in a time- and l-DOPA-concentration-dependent manner, suggesting the uptake of l-DOPA by MAEC and indicating the presence of aromatic l-amino acid decarboxylase (AADC). This was confirmed by the decreased DA content in the presence of benserazide, an AADC inhibitor. Neither d-DOPA nor DA uptake blockers such as mazindol and GBR 12935 significantly affected l-DOPA uptake and hence DA levels. Further, synthesis of DA from l-DOPA was decreased in the presence of the amino acids tyrosine, phenylalanine and tryptophan, whereas the amino acids glycine and proline were without any significant effect. These findings suggest that MAEC have the capacity to selectively take up and decarboxylate l-DOPA with subsequent production of DA.

Localization of ubiquitin carboxyl-terminal hydrolase-L1 in cynomolgus monkey placentas

Ubiquitin carboxyl-terminal hydrolase-L1 (UCH-L1) is a restrictedly expressed enzyme in neural and reproductive tissues, and it is considered to have a significant role in reproduction. In the present study, we investigated the localization of UCH-L1 in placenta of cynomolgus monkeys ( Macaca fascicularis). UCH-L1 protein was detected in cytotrophoblasts of chorionic plate and villi, and decidual cells of decidua basalis in cynomolgus monkey placenta, and the amount of UCH-L1 protein in whole placenta increased as pregnancy progressed. These results supported that UCH-L1 is necessary for placental and fetal development in primate placenta. This is the first report to demonstrate the presence of UCH-L1 in primate placenta, and the cynomolgus monkey may be a useful model for the study of the functions of the ubiquitin–proteasome system in human pregnancy.

Matrix metalloproteinase-28 transcript and protein are expressed in rhesus monkey placenta during early pregnancy.

The role of matrix metalloproteinases (MMP), especially newly described MMP, in trophoblast invasion during human embryo implantation is poorly understood. In this report, using a model of early pregnancy in the rhesus monkey, we have examined the expression and localization of the most recently identified MMP, MMP-28/epilysin, transcript and protein in macaque uterine samples on days 12, 18 and 26 of pregnancy. MMP-28 mRNA expression was shown by in-situ hybridization after day 12 of pregnancy, and both the syncytial and the cytotrophoblastic cell layers of placental villi, the cytotrophoblast cells of the trophoblastic column, and the extravillous trophoblast cells of trophoblastic shell were primary producers of MMP-28 transcript. Expression of MMP-28 mRNA was undetectable in the endovascular trophoblast cells, decidual cells, luminal and glandular epithelium, arterioles, and myometrium. RT-PCR analysis amplified a fragment of 258 nucleotides from rhesus monkey uterine samples containing implantation sites on days 18 and 26. The cDNA fragment, following sequencing, was confirmed to be part of the haemopexin-like domain of MMP-28. It has 95% identity with the corresponding region of human MMP-28 gene. Immunohistochemical analysis further demonstrated that the localization of MMP-28 protein was similar to that of its mRNA. The restricted distribution pattern of this novel MMP in the villous and extravillous trophoblasts during rhesus monkey early pregnancy suggests a potential role in trophoblast invasion associated with embryo implantation.

Placental expression of the nonclassical MHC class I molecule Mamu-AG at implantation in the rhesus monkey.

During human implantation trophoblasts mediate attachment of the embryo to the uterine epithelium and invade and reorganize vessels of the maternal endometrium to initiate blood flow to the intervillous space. Expression of the nonclassical MHC class I molecule HLA-G by invading trophoblasts may play a central role in their protection from recognition by the maternal immune system; however, the ontogeny of trophoblast HLA-G expression during the earliest stages of implantation is difficult to evaluate in human pregnancy. We previously identified a novel nonclassical MHC class I molecule, Mamu-AG, which is expressed in the rhesus monkey placenta and shares many unique characteristics of HLA-G. Immunocytochemical analysis with a Mamu-AG-specific mAb and locus-specific in situ hybridization of rhesus implantation sites 7-12 days after embryo attachment (days 14-19 of pregnancy) demonstrated that Mamu-AG molecules are expressed predominantly in cytotrophoblasts invading the maternal vessels and endometrium, whereas syncytiotrophoblasts covering trophoblastic lacunae or newly formed chorionic villi remained largely Mamu-AG-negative. By day 36 of pregnancy, Mamu-AG glycoprotein also was expressed in villous syncytiotrophoblasts, and accumulation of Mamu-AG glycoprotein was noted at the border between maternal decidua and fetal trophoblasts. The ontogeny of a nonclassical MHC class I molecule at the implantation site supports the hypothesis that its expression is important for the establishment of maternal-fetal immune tolerance.

Cloning and characterization of bonnet monkey GnRH receptor.

Gonadotrophin releasing hormone (GnRH) plays an important role in the reproductive processes of both males and females. It is synthesized by the hypothalamus and binds to a specific receptor on the pituitary to bring about the release of the gonadotrophins, lutineizing hormone and follicle stimulating hormone, which in turn bring about the release of the gonadal steroids. Although the structure of the GnRH receptor (GnRHR) has been elucidated from a number of sources, no information is available about the receptor from the non-human primate species. Here we report the cloning and characterization of the receptor from the pituitary of the bonnet monkey. Antiserum to a bacterially expressed recombinant fragment was used in Western blot analysis and fluorescence microscopy to demonstrate the presence of GnRHR in both human and monkey placentae and pituitary.

Expression of Urokinase, Plasminogen Activator Inhibitors and Urokinase Receptor in Pregnant Rhesus Monkey Uterus During Early Placentation

We have investigated plasmin mediated proteolysis associated with trophoblast invasion during early stages of pregnancy in the rhesus monkey. In situ hybridization and immunocytochemical localization were used to define the cellular and tissue distribution of urokinase plasminogen activator (uPA), plasminogen activator inhibitor type 1 (PAI-1) and 2 (PAI-2) and urokinase receptor in early monkey placenta and uterus. Our results indicate: (1) uPA is expressed in proliferating and invasive cytotrophoblast located in chorionic villi as well as in extravillous trophoblast associated with uterine arterioles. This raises the possibility that urokinase may play an important role in trophoblast invasion. (2) PAI-1 mRNA is specifically localized in two areas where invasive trophoblast cells encounter maternal tissue directly. The extravillous cytotrophoblast cells at the maternofetal junction express PAI-1 mRNA. The invasive endovascular trophoblast cells within the uterine arterioles also express PAI-1 mRNA. The location sensitive expression of PAI-1 mRNA at the maternofetal junction may imply a protective function of this protease inhibitor that might be induced through interaction with decidual cells. (3) Urokinase receptor antigen has also been found at the maternofetal junction and in endovascular trophoblast cells of the invaded maternal blood vessel. (4) PAI-2 immunoreactivity is found in association with cytotrophoblast cells in anchoring choronic villi suggesting its association with early placentation. In conclusion, we propose that the plasmin/plasminogen activator system may not only regulate extracellular matrix degradation, but also modify migration and invasive behaviour of extravillous trophoblast cells, during early placentation.

Expression of tissue type and urokinase type plasminogen activators as well as plasminogen activator inhibitor type-1 and type-2 in human and rhesus monkey placenta

The distribution of mRNAs and antigens of tissue type (t) and urokinase type (u) plasminogen activators (PA) plus their corresponding inhibitors, type-1 (PAI-1) and type-2 (PAI-2) were studied in human and rhesus monkey placentae by in situ hybridisation and immunocytochemistry. Specific monkey cRNA and antibodies against human tPA, uPA, PAI-1 and PAI-2 were used as probes. The following results were obtained. (1) All the molecules tPA, uPA, PAI-1 and PAI-2 and their mRNAs were identified in the majority of the extravillous cytotrophoblast cells of the decidual layer between Rohr's and Nitabuch's striae and in cytotrophoblast cells of the chorionic plate, basal plate, intercotyledonary septae and cytotrophoblast cells of the chorionic villous tree. (2) Expression of uPA and PAI-2 was noted in villous trophoblast whereas tPA and PAI-1 were mainly concentrated where detachment from maternal tissue occurs. (3) No expression of tPA, uPA, PAI-1 and PAI-2 was observed in the basal plate endometrial stromal cells, chorionic plate connective tissue cells, septal endometrial stromal cells or villous core mesenchyme. (4) The distribution of probes observed following in situ hybridisation is generally consistent with the immunofluorescence pattern of the corresponding antigens and no significant interspecies differences were noted. It is possible that both decidual and extravillous trophoblast cells of placentae of human and rhesus monkey are capable of producing tPA, uPA, PAI-1 and PAI-2 to differing extents. Coordinated expression of these genes in the tissue may play an essential role in the maintenance of normal placentation and parturition. The differences in distribution we observed are consistent with the suggestion that coordinated expression of tPA and its inhibitor PAI-1 may play a key role in fibrinolytic activity in the early stages of placentation and separation of placenta from maternal tissue at term. On the other hand, uPA with its inhibitor PAI-2 appears mainly to play a role in degradation of trophoblast cell-associated extracellular matrix, and thus may be of greatest importance during early stages of placentation.

Expression of tissue type and urokinase type plasminogen activators as well as plasminogen activator inhibitor type-1 and type-2 in human and rhesus monkey placenta.

The distribution of mRNAs and antigens of tissue type (t) and urokinase type (u) plasminogen activators (PA) plus their corresponding inhibitors, type-1 (PAI-1) and type-2 (PAI-2) were studied in human and rhesus monkey placentae by in situ hybridisation and immunocytochemistry. Specific monkey cRNA and antibodies against human tPA, uPA, PAI-1 and PAI-2 were used as probes. The following results were obtained. (1) All the molecules tPA, uPA, PAI-1 and PAI-2 and their mRNAs were identified in the majority of the extravillous cytotrophoblast cells of the decidual layer between Rohr's and Nitabuch's striae and in cytotrophoblast cells of the chorionic plate, basal plate, intercotyledonary septae and cytotrophoblast cells of the chorionic villous tree. (2) Expression of uPA and PAI-2 was noted in villous trophoblast whereas tPA and PAI-1 were mainly concentrated where detachment from maternal tissue occurs. (3) No expression of tPA, uPA, PAI-1 and PAI-2 was observed in the basal plate endometrial stromal cells, chorionic plate connective tissue cells, septal endometrial stromal cells or villous core mesenchyme. (4) The distribution of probes observed following in situ hybridisation is generally consistent with the immunofluorescence pattern of the corresponding antigens and no significant interspecies differences were noted. It is possible that both decidual and extravillous trophoblast cells of placentae of human and rhesus monkey are capable of producing tPA, uPA, PAI-1 and PAI-2 to differing extents. Coordinated expression of these genes in the tissue may play an essential role in the maintenance of normal placentation and parturition. The differences in distribution we observed are consistent with the suggestion that coordinated expression of tPA and its inhibitor PAI-1 may play a key role in fibrinolytic activity in the early stages of placentation and separation of placenta from maternal tissue at term. On the other hand, uPA with its inhibitor PAI-2 appears mainly to play a role in degradation of trophoblast cell-associated extracellular matrix, and thus may be of greatest importance during early stages of placentation.