[Trophoblast in villi of the early human chorion according to the data of optico-structural analysis and electron microscopy]

Presence of nuclei with tetraploid content of DNA in syncytiotrophoblast of the early chorion has been demonstrated. Before 8 weeks of pregnancy their content makes 31% and then it drops up to 26%. At this age certain severe changes are revealed in texture characteristics of the nucleus--asymmetry and kurtosis of chromatin distribution. Possible pathways of ultrastructural rearrangements in epithelium of the early chorion are discussed.

Ultrastructure of trophoblast giant cell transformation during the invasive stage of implantation of the mouse embryo

The fine structure of abembryonic and mural trophoblast cells of mouse embryos was analyzed during the initial stages of invasion of the endometrial stroma by the embryo (days 6-8 of pregnancy). On day 6 of pregnancy, most trophoblastic cells are flat and have spindle-shaped nuclei. A few large, round trophoblastic cells (giant cells) are present at the abembryonic pole. As pregnancy proceeds through days 7 and 8, the area occupied by the trophoblast becomes larger because of an increase in the trophoblastic cell population, growth of giant cells, and rearrangement of the latter cells into a network containing maternal blood. As flat cells transform into giant cells, their content of ribosomes, granular endoplasmic reticulum, Golgi complexes, lysosomelike bodies, and heterophagosomes increases. Reichert's membrane is always lined by cell bodies or by laminar processes of trophoblastic cells that are provided with small pores. Transformation of flat cells into giant cells is associated with an activation of the giant cells and their acquisition of invasive behavior.

[The expression of c-myc, c-fms, c-sis oncogenes in the trophoblast of normal pregnancy and trophoblastic disease]

Recently it has been suggested that proto-oncogene plays a role not only in cellular proliferation, development and differentiation, but also in neoplastic transformation. We now show the expression and its localization of c-myc, c-fms and c-sis proto-oncogenes in human developing chorionic tissue and fresh surgical specimens of mole and choriocarcinoma with the method of Northern blotting and In-situ hybridization. The 2.4kb c-myc transcript has been localized to the cytotrophoblast in early placenta and also localized to the C and S typed trophoblastic cells in mole and choriocarcinoma. The 4.0kb c-fms transcript has been localized to the syncytiotrophoblast, especially the highly differentiated syncytiotrophoblast in the second and third trimesters and S typed trophoblastic cells in mole and choriocarcinoma. Moreover, the 4.0kb c-sis transcript has been localized to the cytotrophoblast in early placenta, but not detected in mole or choriocarcinoma. First, these results suggest that the stage and site specific expression of c-myc, c-fms and c-sis proto-oncogenes are clearly related to the proliferation, development and differentiation of normal trophoblastic cells. Second, the expression of c-myc, c-fms proto-oncogenes may be of particular importance in the tumorigenesis and progression of trophoblastic disease.

[Ultrastructural features of the nucleus and cytoplasm of rat trophoblast cells of the connective zone of the placenta and labyrinth]

Ultrastructural organization of the rat trophoblast cells in the connective zone of placenta and labyrinth was investigated on the 12-14th days of gestation. A clear distinction was revealed in the cytoplasm ultrastructure of two cell subpopulations within the connective zone of placenta, i.e. glycogen and trophospongium cells. The former display a well defined network of long thin channels of granular endoplasmic reticulum situated mainly around the glycogen clusters. On the contrary, the latter are rich in the smooth endoplasmic reticulum but lacking glycogen accumulation. Differences in the nucleolar ultrastructure in these two cell subpopulations are not very considerable. A characteristic feature of glycogen cells is the presence of numerous round or oval small-fibrillar nucleolus-like bodies with the diameter of granules 20 nm. The trophoblast cells of the labyrinth are heavily laden with polysomes, which sometimes attach to short channels of the granular endoplasmic reticulum. Not often there occur short profiles of the agranular endoplasmic reticulum. Nucleolus-like bodies are found in all the cell types examined. This means that the nucleolus-like bodies may arise not only on the lampbrush chromosomes in the oocytes or polytene chromosomes, but also in the somatic cells which are capable of dividing mitotically.

Regulation of mouse trophoblast giant cell nucleus development in hatched mouse blastocysts by cyclic cytidine 3',5'-monophosphate (cCMP)

The dibutyryl analog of cCMP enlarged the nuclei of trophoblast giant cells and promoted blastocyst development. The result suggests that cCMP has a trophic effect on embryonic development, specifically by altering the size of the trophoblast cell nucleus but does not enhance trophoblast cell proliferation processes.

Receptors for alpha 2-macroglobulin- and pregnancy zone protein-proteinase complexes in the human placental syncytiotrophoblast

Receptors for complexes between alpha 2-macroglobulin (alpha 2M) and proteinases (e.g. trypsin) were identified and characterized in the human placenta. The receptors also bound the complex formed between pregnancy zone protein (PZP) and chymotrypsin, although with slightly lower affinity, whereas binding of alpha 2M or PZP in their native forms was negligible. Treatment with methylamine to cleave the internal thiol esters caused an increase in binding affinity of alpha 2M to the level of alpha 2M-trypsin but only a minor increase in the affinity of PZP. Chorionic villi prepared from normal full-term placentae were approximately half occupied by endogenous alpha 2M or PZP complexes. These ligands, as well as prebound 125I-labelled alpha 2M-trypsin, were rapidly removed by the addition of 5 mM EDTA. Binding was similar in villi from eight-week and full-term placentae. Autoradiography showed that labelled alpha 2M-trypsin was associated with the syncytiotrophoblast. The kinetics of 125I-labelled alpha 2M-trypsin binding at 4 degrees C was similar in isolated villi and microvillous membranes. Association was slow, with apparent equilibrium by about 16 h. Dissociation of prebound tracer was slow but markedly accelerated in the presence of unlabelled ligand at a saturating concentration. The concentration-dependence of binding at equilibrium yielded a non-linear Scatchard plot. Most of the binding of ligand at tracer concentration was accounted for by high-affinity receptors with a dissociation constant (Kd) of about 50 pM. The content of high-affinity receptors in one placenta was estimated as approximately 125 pmol, i.e., a significant fraction of the total receptor population in the pregnant woman.

The behavior of heterochromatin in mouse and human nuclei

The arrangement of heterochromatin in various human and mouse nuclei has been analyzed with C banding. In most nuclei of 7-day mouse trophoblast, the heterochromatin consists of twin dots, or bigger clumps, apparently attached to the nuclear membrane. This finding agrees with the observation that most of these nuclei, which range from diploid to highly polyploid, show endomitotic stages. No polarization of heterochromatin in a Rabl orientation is seen in the trophoblast nuclei. Neither is a Rabl orientation found in the interphases of cultured human lymphocytes or fibroblasts. From their telophase arrangement, the chromosomes have obviously spread rapidly around the nuclear membrane. In many of the giant mouse trophoblast cells in vivo and in vitro, heterochromatin is apparently underreplicated. The same is true of giant cells in human hydatidiform moles and cervical cancer. Of the 82 cervical cancers analyzed, 46 showed chromocenters, and each tumor was characterized by its own pattern of heterochromatin.

Early human pregnancy in vitro utilizing an artificially perfused uterus

The penetration of luminal epithelium in the uterine cavity represents the crucial event that triggers the failure of embryo implant, thus limiting the possibility of fertility control. The purpose of our study was to implant a human blastocyst, cultured in vitro, into a human uterus extracorporeally perfused with an oxygenated medium. For this purpose, human blastocysts, collected from patients who underwent IVF program because of irreparable tubal infertility, were injected under the luminal epithelium of human perfused uteri. Light and electron microscopy showed that human blastocyst can successfully undergo the stage of implantation and trophoblastic invasion in 52 hours of extracorporeal perfusion.

Loss of polar trophoblast during differentiation of the blastocyst of the horse

Twelve blastocysts, collected 7-12 days after ovulation (Day 0), were examined by light and electron microscopy to investigate the nature of the relationship of the polar trophoblast (Rauber's layer) to the inner cell mass. On Day 7, the polar trophoblast was intact and formed a flattened layer overlying the epiblast cells of the inner cell mass. As blastocysts enlarged to greater than 1 mm in diameter, small discontinuities appeared in the polar trophoblast, where epiblast cells intruded onto the surface. At this time, trophoblast cells adhered closely to adjacent and underlying epiblast cells, forming an irregular layer of cells capping the epiblast. With continued increase in blastocyst size, polar trophoblast cells became isolated but maintained their characteristic apical endocytic structures. By Days 10-12, the scattered trophoblast cells showed evidence of deterioration, and vacuoles containing cell debris were common within the epiblast. It is suggested that polar trophoblast cells become scattered, rather than withdrawing as a unit, because they become more adherent to subjacent epiblast cells than to adjacent trophoblast cells. It is further suggested that most of the isolated cells are eventually phagocytosed by epiblast cells.

Formation and differentiation of extraembryonic mesoderm in the rhesus monkey

Differentiation of extraembryonic mesoderm in the rhesus monkey was studied from the epithelial penetration stage of implantation (stage 4) through the first week of postimplantation development (to stage 6). It was found that the first cells that appeared between the primitive endoderm (hypoblast) and trophoblast were separated from the latter by a basal lamina but appeared to be either loosely attached to the endoderm or to have been detached from it. Cells in this intermediate position differentiated cytologically into mesenchymal cells, which, by stage 5, had a distinctive intraendoplasmic reticulum marker. This differentiation occurred prior to the time at which the primitive streak could be recognized. By the time the primitive streak was readily discernible (stage 6), the extraembryonic mesoderm had already produced substantial extracellular matrix. The sequence of differentiation was repeated, with a 1- to 2-day lag, in the secondary implantation site. No evidence of a contribution from cytotrophoblast or primitive streak to the extraembryonic mesoderm was found. It is concluded that the origin of the first extraembryonic mesoderm in the rhesus monkey is probably a two-step process, with formation of a reticulum from primitive endoderm followed by differentiation in situ into mesenchymal cells. The first blood vessels formed also differentiated in situ from the extraembryonic mesenchymal cells. Primitive capillaries were identifiable as early as the 13th day of pregnancy.

Expression of C-type viral particles at implantation in the marmoset monkey

Type C RNA retroviral particles have been observed budding from the plasma membrane of syncytiotrophoblast during a study of embryo implantation in the common marmoset (Callithrix jacchus). These viral particles appear in profusion at the interface of syncytiotrophoblast with cytotrophoblast. They appear to be a non-infective, endogenous viral component of the host genome, although the precise role of the C-type virus in this context is unclear at present. Such viral particles have been reported previously from studies of human term placenta; however, this is the first report indicating that expression of viral particles occurs at the earliest stages of embryo implantation.

3,5,3'-triiodo-L-thyronine binding sites in nuclei of human trophoblastic cells

Nuclear binding sites of T3 in human trophoblastic cells were biochemically characterized. Nuclei were isolated by a combination procedure with mild homogenization of the freshly obtained trophoblastic tissue aged term gestation, centrifugations and Triton X-100 treatment. The isolated nuclei were incubated with various concentrations of 125I-T3 at 20 degrees C for 3 h. The total number of T3 binding sites per nucleus was approximately 650. The apparent association constant (Ka) was 6.0 X 10(9)M-1. Nuclear proteins extracted from purified nuclei with 0.4M KCl were able to bind T3 giving rise to nuclear thyroid hormone binding protein-T3 complexes and they were precipitated with bovine IgG, as a carrier protein, by 12.5% polyethylene glycol. Binding was maximum in 3 h incubation at 20 degrees C or in 18 h at 0 degrees C, while it dropped quickly at 37 degrees C. The binding characteristics were analyzed by Scatchard plots. In nuclear proteins obtained from 8 term placentae there was a single set of high affinity-low capacity T3 binding sites with Ka of 7.0 X 10(9)M-1. The capacity is about 62.7 fmol T3/mg DNA. The binding sites were found to be specific for L-T3, while L-T4 was about 100-fold less effective, rT3 ineffective, and D-T3 and D-T4 were roughly 1/8 and 1/5 as active as L-T3 and L-T4, respectively in displacing 125I-T3 from the binding sites. These data confirmed that human placenta is a target organ of thyroid hormones; trophoblastic cells contain T3 nuclear receptors which are biochemically similar to those isolated from liver, although the capacity is low.

Human trophoblast cells cultured in modified medium and supported by extracellular matrix

This paper describes a culture procedure which consistently yields 80 to 90 per cent trophoblast from human first-trimester placentae. The trophoblast cells are selected and maintained but there is no increase in proliferation. The cultured cells are found to resemble extravillous rather than villous trophoblast in their immunocytochemical characteristics. This technique provides a means of obtaining human trophoblast cells with a sufficient degree of homogeneity and viability to be used for in vitro experiments.

Fibronectin localization in the mouse embryo from the blastocyst stage to the egg cylinder stage in vitro

Fibronectin has the characteristics of adhesiveness and cell migration promotion which may play important roles in embryo implantation. Using the direct and indirect immunofluorescence techniques, we found fibronectin on the blastocyst, and the trophoblast cells of the egg cylinder stage embryo, especially at the sites of cell spreading, as well as the inner cell mass. The results show that (i) fibronectin is used for the initial cell attachment to the plastic dish, and (ii) during the course of embryo growth in vitro, the trophoblast cells spread over the plastic dish in the area of cells which contain many granules of fibronectin.

Evidence for the involvement of the transcortin carbohydrate moiety in the glycoprotein interaction with the plasma membrane of human placental syncytiotrophoblast

We have studied the interaction of human transcortin and the pregnancy-associated transcortin variant with the microvesicular membrane fraction derived from the human placental syncytiotrophoblast. Two classes of specific binding sites for these glycoproteins were found in this membrane preparation. One of these displays a relatively high binding capacity, Bmax = 140 +/- 60 fmol transcortin per mg membrane protein, and a significantly higher affinity for transcortin, Kd = (1.6 +/- 0.6).10(-10) mol/l, than for the pregnancy-associated variant, Kd = (4.5 +/- 1.2).10(-9) mol/l. On the contrary, another class of the binding sites, occurring in the membranes at a far lower concentration: Bmax = 3.0 +/- 2.2 fmol transcortin per mg membrane protein, shows a higher affinity for the pregnancy-associated transcortin variant, Kd = (3.3 +/- 2.0).10(-12) mol/l, than for normal transcortin, Kd = (2.5 +/- 0.7).10(-11) mol/l. Since the pregnancy-associated variant differs from normal transcortin with respect to its carbohydrate structures only (Avvakumov, G.V. and Strel'chyonok, O.A. (1987) Biochim. Biophys. Acta 925, 11-16), the results of the present work suggest that the transcortin carbohydrates are directly involved in the specific interaction of this serum hormone-binding globulin with the plasma membrane of the placental syncytiotrophoblast.

DNA-fluorescence of mammalian intra-nucleolar chromatin detected by confocal laser scanning microscopy (CLSM)

The complex spatial DNA distribution in the mammalian interphase nucleus was investigated in Feulgen stained thick sections through mouse trophoblast giant nuclei after Lowicryl embedding. DNA-fluorescence was visualized using confocal laser scanning microscopy. Our results show that the spatial arrangement of major interphase chromatin areas can be precisely documented, including the distribution of small intra-nucleolar chromatin zones.

Cytogenetics of trophoblasts from complete hydatidiform moles

The risk of developing choriocarcinoma following a complete hydatidiform mole (CHM) is 2000-4000 times greater than the risk following a normal pregnancy. To understand more fully the increased susceptibility of the molar trophoblast to malignant transformation, we separated the trophoblastic cells from the stromal cells in 14 complete moles and cultured them for cytogenetic analysis. The numerical and structural abnormalities found were compared with those found in the trophoblasts from normal pregnancy and malignant choriocarcinoma cell lines. The percentage of polyploid cells was 2.8 times greater in molar trophoblasts than in normal trophoblasts. Although we found no consistent chromosomal abnormality in the molar trophoblasts, these cells were significantly more vulnerable to chromosomal breakage than the molar fibroblasts, normal trophoblasts, normal fibroblasts, and maternal decidual cells. Out of a total of 103 breakpoints observed in 338 cells, 42 coincided with known fragile sites, 18 with the location of protooncogenes, 27 with breakpoints reported in other neoplasia, and 18 with breakpoints found in four choriocarcinoma cell lines. The chromosomes in choriocarcinoma cell lines have hypotetraploid mode and many structural rearrangements. Our results suggest that the genetic instability found in the molar trophoblasts may be responsible for progressive karyotypic changes and greater susceptibility to malignant transformation.

Pregnancy-induced structural changes and trophoblastic invasion in the segmental mesometrial arteries of the guinea pig (Cavia porcellus L.)

Light microscopic, electron microscopic and histochemical studies were carried out on the segmental mesometrial arteries of non-pregnant guinea pigs and on pregnant ones at each of the nine weeks of gestation. Pregnant animals show drastic changes in arterial structure and dimensions. Hypertrophy and structural dilatation of the arterial wall are obvious. In midpregnancy, the elastic membranes begin to disappear; only small fragments remain. From the fifth week on, mononuclear cells appear in the media; they form aggregates and occasionally giant cells with signs of phagocytosis in the seventh week of gestation. In the eighth week further degenerative changes can be observed, resulting in widespread destruction of the arterial wall. Deposition of necrotic cell debris is obvious in the ninth week. By this time there appear in the endothelial layer conspicuous single cells, cell aggregates and giant cells with heavily folded nuclei, prominent nucleoli, abundant vesicles, free ribosomes, intracellular lacunae and the histochemical properties of placental trophoblast. These cells in the endothelium are distinctly different from the medial giant cells of mononuclear origin. According to these observations, the segmental mesometrial arteries of pregnant guinea pigs show cytological and structural changes similar to those described for the mesometrial arteries in the hamster and the spiral arteries in man. The results show that, beside structural dilatation, degenerative changes and apparent trophoblastic giant cell invasion occur in the arteries studied. Trophoblastic invasion occurs later than structural dilatation and obviously does not trigger or control the structural dilatation of the segmental mesometrial arteries.

Class I major histocompatibility complex antigen expression on early murine trophoblast and its induction by lymphokines in vitro. II. The role of gamma interferon in the responses of primary and secondary giant cells

The induction of paternal Class I and II MHC antigens by crude lymphokine preparations or purified recombinant gamma interferon was investigated on (C57BL/6J X CBA/H)F1 primary and secondary trophoblast giant cell outgrowths from 3.5-day post-coital (pc) blastocyst and 7.5-day pc ectoplacental cone preparations, respectively, using sensitive immunogold labelling techniques and electron microscopy. Class I MHC (but not Class II) antigens could readily be induced on secondary trophoblast giant cells, by incubation in vitro with gamma interferon for 40 h. However, repeated attempts to induce detectable MHC antigens on primary trophoblast giant cells failed. Mock-treated (C57BL/6J X CBA/H)F1 secondary trophoblast giant cell control preparations failed to express detectable MHC antigens. These findings suggest that, at the time of implantation, there is a time window during which MHC antigens are neither expressed constitutively nor are inducible by soluble factors which normally modulate cell surface MHC antigen concentration.

Human cytomegalovirus infection of human placental explants in culture: histologic and immunohistochemical studies

The induction of human cytomegalovirus infection in human first-trimester placentas was studied with a placental explant culture model. Replication and/or release of human cytomegalovirus in placental explant cultures did not occur at any time from 1 to 10 days after infection when examined by plaque assay and analyses of extracted deoxyribonucleic acids. In contrast, typical human cytomegalovirus-induced histopathologic lesions bearing human cytomegalovirus antigens were consistently localized in the trophoblastic cells covering placental villi. These data clearly demonstrate that placental cells are permissive of latent and/or abortive human cytomegalovirus infection in vitro. Our results support the hypothesis that during human cytomegalovirus infection of pregnant women, maternal viremia or intrauterine infection results in latent human cytomegalovirus infection of placental cells that may persist during the course of pregnancy.