Histologic characteristics of cells cultured from rat placental tissue

GM-CSF and CSF-1 stimulate DNA synthesis but not cell proliferation in short-term cultures of mid-gestation murine trophoblast

Short-term cultures of purified murine trophoblast were used to investigate the potential trophic effects of a number of cytokines. Both granulocyte-macrophage colony stimulating factor (GM-CSF) and colony stimulating factor-1 (CSF-1) increased [3H]thymidine (TdR) uptake (3-8 times control values) by trophoblast harvested from placentae on day 12 or 14 of pregnancy. In contrast, interleukin-3 (IL-3) had only a mild stimulatory effect ([3H]TdR uptake 1.5 times control), and IL-2 did not alter the level of DNA synthesis in these cells. Immunocytochemical analysis confirmed that the cells engaged in DNA synthesis were cytokeratin-positive trophoblast cells and revealed that these cells predominantly bore markers (alkaline phosphatase, transferrin receptors) characteristic of trophoblast cells from the placental labyrinth. The increased DNA synthesis observed after exposure to GM-CSF or CSF-1 was not associated with a change in the proportion of nuclei involved in synthesis, nor did it result in significantly increased trophoblast cell numbers in the cultures. These findings suggest that DNA-synthesizing trophoblast cells were not proliferating, but were more likely engaged in endoreduplicative cycles leading to the formation of terminally differentiated trophoblast giant cells. These results caution against the presumption of proliferation when measuring [3H]thymidine incorporation by placental or trophoblast cells in standard in vitro cultures. In addition, taken together with the reports of high levels of CSF-1 in the pregnant uterus and the expression of the CSF-1 receptor on placental trophoblast cells, they suggest that the hemopoietic cytokines may play a role in the differentiation and/or function of trophoblast cells in the developing murine placenta.

Whole-cell outward currents in freshly dissociated rat placental cells

1. We applied whole cell voltage clamp techniques to freshly dissociated rat placental cells (20-21 days gestation). Tetraethylammonium (TEA)-sensitive outward currents were recorded in about 50% of cells. 2. The outward current had a reversal potential of -50 mV which is more positive than the potassium equilibrium potential (-82 mV). 3. The bath solution without NaCl decreased the outward current amplitude, while the elimination of only Na ions from the bath solution did not modify the outward current. 4. The results suggest a possible contribution of chloride ions to the outward currents in rat placental cells.

Isolation of phenotypically distinct trophoblast cell lines from normal rat chorioallantoic placentas

Growth characteristics and the expression of trophoblast-associated markers by six cell lines generated from midgestation chorioallantoic placentas of outbred (Holtzman) and inbred (Lewis, PVG.RT Ir8) rats were evaluated. The cells comprising all cell lines were epithelioid (contained cytokeratin-type intermediate filaments), had normal (2n, 4n) DNA content, and synthesized the extracellular matrix glycoprotein laminin. Variability was observed among the lines in all other characteristics: median cell size, rate of growth, serum dependency, responses to transferrin and dibutyryl cyclic adenosine-3',5'-monophosphate, synthesis of some major proteins, alkaline phosphatase activity, and the expression of immunoreactive placental lactogen-II. In general, cell lines with smaller mean cell sizes grew rapidly and required little serum for maintenance in vitro; cell lines with larger mean sizes grew more slowly and preferred higher concentrations of serum. Some associations between mean cell size/rate of growth and other characteristics were observed. No major differences were apparent between cell lines generated from outbred and inbred rat placentas. Trophoblast cell lines expressing distinct phenotypes provide a valuable new approach for studying a wide range of trophoblast cell activities.

The killing of mouse trophoblast cells by granulated metrial gland cells in vitro

Mouse placental cell preparations have been maintained in culture, and the types of cell that attached to the culture dish were classified according to morphological criteria. However, these morphological criteria were insufficient to determine from which trophoblast layer in the placenta all of the types of cell found in the cultures originated. Some placental cell preparations were co-cultured with granulated metrial gland (GMG) cells and these cultures were studied using time-lapse video. Various responses to contacts between GMG cells and trophoblast cells were observed. These responses included the killing of trophoblast cells by GMG cells.

Expression of histocompatibility antigens, transferrin receptors, intermediate filaments, and alkaline phosphatase by in vitro cultured rat placental cells and rat placental cells in situ

Rat placental cells (RPCs) derived from the chorioallantoic placenta of day-12 Holtzman rats were tested for the expression of class I and class II RT I histocompatibility antigens, transferrin receptors, intermediate filaments, and alkaline phosphatase. The binding of mouse monoclonal antibodies to those antigens by RPCs was compared with the binding of the same reagents to rat placental cells in situ. RPCs expressed low levels of class I antigens and failed to express detectable levels of class II antigens. RPCs resisted up-regulation of expression of class I antigens by interferon-gamma, and did not express class II antigens following exposure to medium containing interferon. Transferrin receptors; cytokeratin intermediate filaments, and alkaline phosphatase were universally expressed by RPCs. Taken together with the patterns of expression of the same antigens by rat placental cells in situ, the results suggest that RPCs comprise labyrinthine trophoblast cells. Those cells may provide a valuable new approach for studying the structures and functions of trophoblast cells in vitro.

Ultrastructure of cultured rat placental cells

Rat placental cells (RPCs) derived from explants of gestation day 12 chorioallantoic placental primordia were propagated as ascites RPCs and as in vitro cultured RPCs. Although the morphological characteristics of ascites RPCs and in vitro cultured RPCs differed markedly by light microscopy, evaluation by electron microscopy revealed that all RPCs were epithelioid. Morphological differences at the light microscope level were attributable to environmental conditions. When RPCs were compared with placental cells in situ, RPC characteristics most closely resembled those of layer-one trophoblast cells (germinal cytotrophoblast) present in the labyrinthine region of the placenta. RPCs, which appear to be a relatively homogeneous population of trophoblast cells, may be valuable tools for evaluating the relationships between maternal and fetal cells during pregnancy and for studying the growth and differentiation of extraembryonic cells.

Isolation and characterization of rat trophoblast cells

Previous immunohistochemical studies of the rat placenta using specific alloantisera and/or monoclonal antibodies showed that the basal zone trophoblasts stained for Pa and Aa class I major histocompatibility complex (MHC) antigens and for the human SP1-related antigen. In an effort to isolate the basal zone trophoblast cells from the rat placenta, we used these markers to assess the degree of purification of the cells separated by density gradient centrifugation using either Ficoll-Hypaque or Percoll as the gradient medium. The cells were put either on the top or at the bottom of discontinuous density gradients in the range of 1.005-1.10 g/ml. The cell separation profiles for the two media were different. With Percoll, most of the trophoblast cells (80-95%) were collected at the density gradients 1.04/1.06 and 1.06/1.08, whereas with Ficoll-Hypaque, these gradients separated only a small fraction (4-23%) of the trophoblast cells, and most of them pelleted at the bottom of the tube. The trophoblast cells separated by Ficoll-Hypaque, however, showed fewer contaminant cells than those separated by the Percoll gradients.

Uptake of transferrin and iron by cultured rat placental cells

This paper describes a method for the culture of rat placental cells. The method involved separation of the basal layer from the labyrinth and sequential digestion of the cells. The cells were demonstrated not to be fibroblasts and are described in terms of their appearance under the light and electron microscopes. Transferrin and iron uptake by the cells was examined and compared with results achieved using other methods of study. The results showed that transferrin bound to receptors on the cell surface and that the transferrin, once bound, was taken into the cell. Only this internalized transferrin was capable of donating iron to the cells. The iron was accumulated within the cells and did not appear to be released to the incubation medium. The apparent dissociation constant (Ka) for transferrin was found to be 6.96 X 10(6) M-1, a value similar to that described by earlier workers. The placental cells had 3.4 X 10(11) binding sites/microgram DNA, equivalent to approximately 1 X 10(6) sites/cell. From these data, and from the rate of accumulation of iron by the cells, the receptor turnover time was estimated as being between 5 and 10 min.

The effect of alpha-fetoprotein on the growth of placental cells in vitro

Cell cultures of early mouse placentae were studied in the presence of mouse amniotic fluid or isolated alpha-fetoprotein (AFP). Four cell types were observed: polygonal cells, giant cells, small round cells and fibroblasts. The number of polygonal cells increased in placental cultures in the presence of amniotic fluid or AFP, suggesting de novo formation and proliferation in vitro. These preparations were found to stimulate the DNA synthesis in polygonal cells, as demonstrated by 3H-thymidine labelling experiments. Polygonal cells also show a significant increase in 3H-leucine incorporation, indicating more active protein synthesis under the effect of amniotic fluid or AFP. These data suggest that AFP may be one of the fetal factors promoting trophoblastic differentiation.

Immunological studies of mouse decidual cells. I. Membrane markers of decidual cells in the days after implantation

Mouse decidual cell suspensions from day 6 to day 8 of gestation were prepared by enzymatic treatment with collagenase and trypsin and tested for various membrane markers. (a) Besides H-2 antigens, Thy-1 antigens are present on about 50% of the cells; this may reflect the fibroblastic origin of decidual cells or be a marker expressed on some decidual cells possibly under hormonal control. (b) T or B lymphocytes, as defined by four Lyt antigens or surface immunoglobulins, are not present in significant amounts. (c) A substantial number of cells bearing receptors for the Fc portion of IgG (FcR) is detectable in the decidua, probably closely connected with trophoblast cells; these FcR-bearing cells may act in preventing excessive invasion of uterine tissue by trophoblast or could contribute to the protection of the embryo by interacting with maternal blocking antibodies and trophoblast. No receptors for for complement were detected, even after 16-20 h in culture after trypsin treatment.