The enhancers of the human placental lactogen B, A, and L genes: progressive activation during in vitro trophoblast differentiation and importance of the DF-3 element in determining their respective activities

The hCS-A and hCS-B genes encoding human chorionic somatomammotropin and the related hCS-L gene are very similar in their coding and flanking sequences. For each of these genes, downstream enhancers, varying in strength, have been identified with the help of cytotrophoblast-derived JEG-3 cells, which do not express the hCS genes. Here we study the activity of the hCS enhancers in human syncytiotrophoblast in primary culture, which naturally expresses the hCS genes. We show that the activity of the hCS-B gene enhancer is mediated by two elements, DF-3 and DF-4, whereas the hCS-L and hCS-A gene enhancers display weaker activity due to mutations in their respective DF-3 sites. Replacement of the hCS-B DF-3 site with the homologous hCS-A sequence causes hCS-B enhancer activity to decrease. Primary cytotrophoblasts differentiate in culture to form the syncytiotrophoblast. We show that during this process the production of hCS progressively increases and that concomitantly all three hCS enhancers are progressively activated. A targeted mutation in the 3' part of the DF-4 element abolishes the binding of a protein present only in syncytiotrophoblast extracts and inactivates the DF-4 element. Thus, a direct correlation exists between the appearance of this syncytiotrophoblast-specific protein and hCS enhancer activity. This primary culture model proves useful in studying the regulation of the hCS genes.

The ARP-1 orphan receptor represses steroid-mediated stimulation of human placental lactogen gene expression

Studies were performed to determine whether ARP-1, which is an orphan receptor of the steroid receptor superfamily, inhibits basal activity of the human placental lactogen (hPL) promoter and the increase in hPL promoter activity in response to the receptors for thyroid hormone (TR) and retinoic acid (RAR). Co-transfection of an ARP-1 expression vector into BeWo choriocarcinoma cells, along with an expression vector containing 1.2 kb of the hPL promoter coupled to a CAT reporter gene, resulted in a dose-dependent inhibition of basal CAT activity. In addition, ARP-1 inhibited the stimulation of CAT activity by RAR alpha and TR beta expression vectors. Mobility shift assays demonstrated that ARP-1 binds specifically to a composite steroid response element on the hPL promoter that confers retinoic acid and T3 responsiveness. The results implicate an inhibitory role for ARP-1 in the regulation of hPL gene expression and strongly suggest that hPL gene expression is regulated, at least in part, by the interaction of stimulatory and inhibitory members of the steroid receptor superfamily.

Selective modification of recombinant bovine placental lactogen by site-directed mutagenesis at its C terminus

Five recombinant analogues of bovine placental lactogen (bPL) ((bPL(S184H), bPL(S187A), bPL(S187F), bPL(T188F), bPL(T188F,I190F)) were prepared, expressed in Escherichia coli, and purified to homogeneity. Circular dichroism analysis revealed no or minor structural changes, except in bPL(T188F,I190F). Binding and biological activities of bPL(T188F,I190F) were almost completely abolished, whereas bPL analogues mutated at position 187 retained their full activity. Point mutation T188F resulted in selective modification; binding to somatogenic receptors, their extracellular domains (ECDs), and to bPLR in the endometrium as well as somatogenic receptor-mediated biological activities were reduced or abolished, whereas binding to lactogenic receptors, their ECDs, and subsequent biological activity was fully or almost fully retained. This selective modification most likely results from a steric hindrance induced by a bulky Phe-188 chain of bPL which interacts with the Arg-43 of the human or Leu-43 of the non-human GHRs. Point mutation S184H abolished the interaction with hGHR, most likely due to the unfavorable charge-charge interaction, possibly accompanied by steric hindrance between Arg-43 of the receptor and the newly introduced His-184 and possible interference with the putative interaction between the alkyl portion of Thr-188 and Lys-185 of bPL with Trp-104 of hGHR. In contrast, bPL(S184H) retained its capacity to interact with nonhuman GHRs. Decrease in the biological activity of bPL(S184H) was also observed in two lactogenic receptor-mediated bioassays most likely due to the elimination of the intermolecular hydrogen bond of Ser-184 with a side chain of Tyr-127, which appears in all lactogenic receptors.

Long-term dual perfusion of isolated human placental lobules with improved oxygenation for infectious diseases research

An improved method for long-term perfusion of the isolated human term placental lobule has been developed to investigate the maternofetal transfer of infectious agents, in particular the human immunodeficiency virus (HIV). The purpose of this paper is to describe those modifications that allow for substantially prolonged perfusions in in a biohazard environment. The method described has been adapted from previous models. The perfusion apparatus has been modified for use within a biohazard hood, and, intravenous bags contain the medium for circulation of perfusates in closed circuits. A Mera Silox-S 0.3 membrane oxygenator delivers more oxygen to the tissue, and, Electromedic Cardioplegia heat exchangers warm the perfusate prior to oxygenation. Viability criteria (glucose consumption, lactate production, de novo production of human placental lactogen (hPL), volume loss, flow, temperature, pressure, oxygen transfer, carbon dioxide production, absence of IgM transfer and light and electron microscopy) demonstrate that the placental tissue remains in a functional state throughout the perfusion. Oxygen and glucose consumption are both stable over time; lactate levels remain constant; and hPL continues to be produced. These significant modifications of the perfusion system have permitted the investigators to increase the duration of perfusion to 48 h while preserving normal metabolic function of ultrastructurally intact tissue as demonstrated by ultra structural observations. This perfusion model device provides biohazard precautions and may be applied to other studies of placental physiology.

Apolipoprotein A-I stimulates placental lactogen expression by human trophoblast cells

Earlier studies from our laboratory indicated that apolipoprotein A-I (Apo A-I) stimulates the acute release of human placental lactogen (hPL) from trophoblast cells in culture. We have now demonstrated that Apo A-I also causes a secondary increase in hPL release, beginning about 6 h after exposure to Apo A-I, that is blocked by cycloheximide and actinomycin D. Apo A-I also stimulated a dose-dependent increase in hPL promoter activity in JAR cells transfected with a 1.1-kilobase (-1078/2) fragment of the hPL3 promoter coupled to a chloramphenicol acetyltransferase (CAT) reporter gene. Maximal stimulation, 5.2-fold above basal levels, occurred at an Apo A-I concentration of 1.5 mg/ml, which is within the physiological concentration of Apo A-I during pregnancy. 37pA, a synthetic amphipathic peptide that mimics the secondary structure of Apo A-I and stimulates the synthesis and release of hPL, also stimulated a dose-dependent increase in CAT activity, with maximal stimulation comparable to that caused by Apo A-I. In addition, Apo A-I stimulated a modest increase in CAT activity in BeWo choriocarcinoma cells, Chinese hamster ovary cells, and HeLa cells. However, the maximal stimulation of hPL promoter activity in the Chinese hamster ovary and HeLa cells (approximately 2.5-fold above basal levels) was less than that in choriocarcinoma cells, suggesting that trophoblast cell nuclear factors may be necessary for maximal expression of the promoter in response to Apo A-I. Taken together, these results indicate that Apo A-I stimulates hPL gene expression, and that DNA elements in the first 1.1 kilobase of the promoter are sufficient for transactivation by Apo A-I.

Cytokines that use gp130 as a signal transducer stimulate mouse placental lactogen-I (mPL-I) but inhibit mPL-II production in vitro

Interleukin-11 (IL-11), leukemia inhibitory factor (LIF), and oncostatin M (OM), all of which use gp130 as a signal transducer, significantly inhibited mouse placental lactogen-II (mPL-II) secretion by cultured placental cells from Days 7, 9, and 12 of pregnancy. These cytokines significantly stimulated mPL-I secretion by cells from Day 9, but not Day 7, of pregnancy. An antibody to LIF completely blocked the stimulatory and inhibitory effects of LIF on mPL-I and mPL-II secretion, respectively. LIF and OM decreased the abundance of mPL-II mRNA in placental cells. Double immunocytochemistry for mPL-I and mPL-II indicated that LIF, OM, and IL-11 significantly increased the number of giant cells containing only mPL-I or both mPL-I and mPL-II but decreased the number of giant cells containing only mPL-II. IL-6, which also uses gp130 as a signal transducer, inhibits mPL-II secretion only after midpregnancy; however, addition of soluble IL-6 receptor (sIL-6R) together with IL-6 resulted in a significant inhibition of mPL-II secretion before midpregnancy. Treatment of cells from Day 12 of pregnancy with IL-6 during the first 2 days of culture resulted in significant inhibition of mPL-II secretion by the third day of culture.(ABSTRACT TRUNCATED AT 250 WORDS)

Opposite effects of transforming growth factor alpha and epidermal growth factor on mouse placental lactogen I secretion

This study was undertaken to determine whether transforming growth factor alpha (TGF-alpha) regulates the production of mouse placental lactogen I (mPL-I) and mPL-II in a manner that is similar to that of epidermal growth factor (EGF), which was previously shown to stimulate mPL-I secretion and inhibit mPL-II secretion. In contrast to the activity of EGF, human (h) and rat (r) TGF-alpha (each at 100 ng/ml) inhibited secretion of mPL-I by placental cells isolated from mice on day 7 of pregnancy. Maximum inhibition of mPL-I secretion occurred on the third day of a 5-day culture period and ranged between 37% and 56% in multiple trials. Incubation of cells with hTGF-alpha and EGF was not followed by a change in the mPL-I concentration of the medium, suggesting the peptides antagonized each other's effects. hTGF-alpha and rTGF-alpha inhibited secretion of mPL-II; maximum inhibition ranged between 62% and 84% in multiple trials. The lowest concentrations of hTGF-alpha that affected mPL-I and mPL-II secretion were 10 ng/ml and 1 ng/ml, respectively. EGF and hTGF-alpha bound to the same receptors on placental cells, as assessed by cross-linking, and both peptides stimulated receptor phosphorylation, as assessed by Western blot analysis. There are three types of mPL-containing cells in placental cultures: cells that contain only mPL-I, cells that contain only mPL-II, and cells that contain both mPLs. The percentage of each type of mPL-containing cell in the culture was determined by immunostaining. hTGF-alpha affected the differentiation of the subpopulations of PL-containing cells in a manner that differed from that of EGF. The data suggest that TGF-alpha and EGF do not regulate the production of mPL-I and mPL-II in a similar manner.

The nuclear factor NF-IL6 activates human placental lactogen gene expression

Transient transfection studies using deletion mutants of the hPL promoter indicate that the DNA elements for NF-IL6 responsiveness are located between -2.3 to -1.1 kb. Subsequent transfection studies using a hPL promoter fragment containing the region between -1376 to -1088 bp ligated to a heterologous SV40 CAT vector (NF-IL6/hPL-CAT) demonstrated that the NF-IL6/hPL-CAT construct is responsive to NF-IL6. Mobility shift assays using nuclear extracts from BeWo choriocarcinoma cells overexpressing NF-IL6 demonstrated specific binding of the extracts to a labeled oligonucleotide probe to this region of the hPL promoter. These studies therefore strongly suggest that the effect of IL-6 on hPL gene expression is mediated, at least in part, by the binding of NF-IL6 to a region of the hPL promoter that contains three NF-IL6 responsive elements.

Involvement of epidermal growth factor (EGF)/EGF receptor autocrine and paracrine mechanism in human trophoblast cells: functional differentiation in vitro

We have studied the expression of epidermal growth factor (EGF) and EGF receptors (EGF-R) in isolated human trophoblast cells at various stages of differentiation and also the biological significance of the EGF/EGF-R autocrine and paracrine mechanism. Cytotrophoblast cells were isolated from human placental tissues of 6-9 weeks of gestation. Trophoblast cells underwent morphological and functional differentiation during in vitro culture. The expression of EGF and EGF-R protein and mRNA was studied in trophoblast cells cultured for 0-5 days, using immunocytochemical staining, and reverse transcription and polymerase chain reaction. Monoclonal antibodies (mAbs) against EGF and EGF-R showed specific staining in trophoblast cells at all stages of differentiation. Both EGF and EGF-R gene transcripts were detected in RNA samples isolated from trophoblast cells at all stages. These data suggest the presence of an EGF/EGF-R autocrine and paracrine mechanism in human trophoblast cells. Next, we examined the biological significance of this mechanism on trophoblast cell differentiation in vitro. EGF added to the culture medium significantly increased human chorionic gonadotrophin-beta (hCG-beta) secretion and, more importantly, anti-EGF neutralizing mAbs significantly reduced both hCG-beta and human placental lactogen secretion from trophoblast cells in culture. All these results suggest that human trophoblast cells express both EGF and EGF-R, and that EGF may play an important role in the functional differentiation of human trophoblast cells.

Macrophage colony-stimulating factor induces the growth and differentiation of normal pregnancy human cytotrophoblast cells and hydatidiform moles but does not induce the growth and differentiation of choriocarcinoma cells

In the present study, we examined whether or not macrophage colony-stimulating factor (M-CSF; CSF-1) is involved in the growth and differentiation of human chorionic, hydatidiform mole and choriocarcinoma cells. M-CSF promotes the growth of early gestation chorionic cells, hydatidiform mole cells, and a human term placenta cell line (tPA30-1). However, the growth of choriocarcinoma cells, BeWo, Jar, Jeg-3, and NUC-1, was not influenced at all by M-CSF. M-CSF promoted the secretion of human chorionic gonadotropin (hCG) and human placental lactogen (hPL), which are secreted from differentiated trophoblast, from early gestation chorionic cells and from hydatidiform mole cells. However, the secretion of hCG and hPL from choriocarcinoma cells was not affected by M-CSF. When M-CSF localization was examined by immunohistochemical staining, M-CSF was detected in chorionic and hydatidiform mole cells, but was absent in choriocarcinoma cells. These results suggest that the growth and differentiation of normal chorionic and hydatidiform mole cells are M-CSF-dependent, while the growth and differentiation of choriocarcinoma cells are not.

Interleukin 6 inhibits mouse placental lactogen II but not mouse placental lactogen I secretion in vitro

The mouse placenta produces several polypeptides belonging to the prolactin-growth hormone gene family, including mouse placental lactogen (mPL) I and mPL-II. The present study was undertaken to determine whether the secretion of mPL-I and mPL-II is regulated by interleukin 6 (IL-6), which is present in the placenta and has previously been reported to stimulate the secretion of pituitary members of this gene family. Effects of human and mouse IL-6 on mPL-I and mPL-II secretion were examined in primary cultures of placental cells from days 7, 9, and 12 of pregnancy. IL-6 caused a dose-dependent reduction in the mPL-II concentration in the medium of cells from days 9 and 12 of pregnancy but did not affect the mPL-II concentration in the medium of cells from day 7 of pregnancy or the mPL-I concentration in the medium of cells from days 7 or 9 of pregnancy. The lowest concentration of human IL-6 that significantly inhibited mPL-II secretion was 250 pM. The effect of IL-6 on the mPL-II concentration in the medium was due primarily to inhibition of mPL-II synthesis, which resulted at least partly from a decrease in the steady-state level of mPL-II mRNA. These data raise the possibility that IL-6 may regulate mPL-II production after midpregnancy in vivo.

Stimulation of rat placental lactogen-II (rPL-II) secretion by cultured trophoblasts by insulin: development of a rat placental cell culture system and effects of peptide hormones on rPL-II secretion in vitro

The purpose of this study was to develop a primary culture system using serum-free medium for rat placental trophoblast cells and to investigate the factors that control rat placental lactogen-II (rPL-II) secretion in vitro. The placentae of day 13 pregnant rats were dissociated in Medium 199 containing 0.1% collagenase and 0.002% DNAase. Dissociated cells were fractionated into five segments by centrifugation through a 40% Percoll density gradient and incubated on rat tail collagen bed in medium SFM-101 for up to 7 days. Fraction B at the Percoll gradient density of 1.05 g ml-1 was enriched with rPL-II-producing cells and the time course of rPL-II secretion was characterized by a rapid increase in the first 2 days, remaining at high values (mean: 14-16 ng micrograms-1 DNA) for the following 2-3 days and decreasing thereafter. The rPL-II-producing cells from faction B identified by immunocytochemical examination accounted for approximately 69% of total cultured cells and consisted of a few giant cells and polygonal cells. Growth factors (bovine insulin, 0.1-20 micrograms ml-1; recombinant human insulin-like growth factor (IGF)-I, IGF-II, 0.1-1.0 micrograms ml-1; murine epidermal growth factor (EGF), 0.001-10 micrograms ml-1), rat pituitary hormones (rat growth hormone, rat prolactin, 0.1-10 micrograms ml-1) and hypothalamic hormones (human growth hormone-releasing hormone (GHRH), corticotrophin-releasing hormone (CRH), LHRH, 0.1-10 micrograms ml-1) were individually added to the culture medium to investigate the putative factors that directly control rPL-II secretion by the trophoblast cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Efficient lipofection of human trophoblast cells in primary cultures

Human choriosomatomammotropic hormone, also known as placental lactogen, is expressed in syncytiotrophoblast cells of the placenta. Studying transcriptional regulation of the genes coding for this hormone, we became interested in transfecting primary cultures of these trophoblast cells. In this study, we show that it is possible to transfect, by the lipofection method, these giant cells in an efficient and reproducible manner. We show the presence of an enhancer region downstream from the hCS-B gene, functionally active in these cells; furthermore, we demonstrate the placenta-specific characteristic of this enhancer, previously identified in a human choriocarcinoma cell line.

Ethanol alters hormone production in cultured human placental trophoblasts

Maternal alcohol abuse during pregnancy can lead to abnormalities in fetal development, including the fetal alcohol syndrome (FAS). Although intrauterine growth retardation is a hallmark of FAS, the pathophysiology is not fully understood. A contributing factor may be altered placental function, which could affect fetal growth and development. As a major endocrine organ during pregnancy, changes in the production of placental hormones could affect pregnancy and possibly fetal development. In this study, the effect of continued exposure to ethanol on placental hormone production was examined using cultured human placental trophoblasts. Ethanol exposure involved diffusion of ethanol from the atmosphere into the culture medium. This was refreshed daily, leading to daily peak concentrations of 280 to 300 mg/dl (60-65 mM) at 16 to 24 hr. This ethanol exposure for 2 or 4 days significantly increased the production of human chorionic gonadotropin and progesterone by the cultured trophoblasts. However, ethanol treatment had no effect on human placental lactogen production. Acute stimulation (10 min) of cultured trophoblasts with adenosine (50 microM) normally results in increased production of cyclic adenosine 3',5'-monophosphate (cAMP). With ethanol exposure, adenosine-stimulated cAMP production was significantly elevated relative to that in controls. However, the effect of ethanol on adenosine-stimulated cAMP did not appear to be secondary to chronic alterations in adenosine in the culture medium. Measurement of adenosine in the culture medium revealed no difference in concentration or production between control and ethanol treated groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of chimerism in sheep-goat concepti that developed from blastomere-aggregation embryos

Chimeric sheep-goat pregnancies were established in 24 ewes and 29 does by transferring 251 embryos, prepared by the blastomere-aggregation technique, to 52 ewes and 61 does. Fifteen does experienced early pregnancy failure; however, term offspring were delivered by 24 ewes (17 lambs, 3 kids, 6 chimeras) and 14 does (6 lambs, 9 kids, 6 chimeras). (Fetal classifications were based on phenotype, red blood cell isozymes, and lymphocyte antigen expression). RIAs for ovine and caprine placental lactogen detected chimerism in the binucleate cell population of the trophoblast throughout the pregnancies of 2 ewes and 7 does; these pregnancies resulted in the birth of 12 healthy offspring. Histological examinations of intact placentomes from 2 of these recipients revealed a continuous cellular trophoblast apposed to a syncytium as in normal placentas. Chimerism was detected electrophoretically in the membranes of the placentas with binucleate cell chimerism and in 17/28 of the other placentas. Data collected on placental lactogen production, chimerism in the conceptus, and placental morphometry were examined with respect to the stages of the blastomeres aggregated to form the chimeric embryo and with respect to fetal status at delivery. For comparison, analogous data were collected on sheep-goat concepti that developed from embryos prepared by inner cell mass transplantation.

Interaction between choriocarcinoma cell line (JAr) and human cytotrophoblasts in vitro

Cytotrophoblasts (from term placentae) and cells from the choriocarcinoma cell line JAr were cultivated either separately or in co-culture for 72 h. RNA was isolated from the cell cultures and Northern blots were developed using equal amounts of RNA. The RNA was hybridized with cDNA probes for CG alpha, CG beta and hPL. Corresponding m-RNAs were detected in the three RNAs except for hPL m-RNA which was absent from JAr cells RNA. The abundance of CG alpha and CG beta m-RNA in the RNA of the co-culture was higher than their accumulative abundances in the RNAs from cytotrophoblasts and JAr cells cultured alone and the abundance of hPL m-RNA in the RNA of the co-cultures was as high as that in the RNA from cytotrophoblasts cultured alone. On the basis of previous findings (Hochberg et al, 1991), it can be assumed that the cytotrophoblasts in the co-cultures are responsible for the increase in hormonal m-RNA production. It could be calculated that the abundances of the CG alpha, CG beta and hPL m-RNAs in the RNA which originated in the cytotrophoblast nuclei were 20, 100 and 10-fold higher respectively in the co-culture compared to those in the culture of cytotrophoblasts. This effect is limited to certain genes only as the concentration of the 92kD collagenase m-RNA and uPA (urokinase type plasminogen activator) m-RNA, which are both produced in cytotrophoblasts to a much higher extent than in JAr cells, and are not increased by cultivating the cytotrophoblasts with JAr cells in co-culture.(ABSTRACT TRUNCATED AT 250 WORDS)

Novel in-frame two codon translational hop during synthesis of bovine placental lactogen in a recombinant strain of Escherichia coli

A recombinant Escherichia coli strain was constructed for the overexpression of bovine placental lactogen (bPL), using a bPL structural gene containing 9 of the rare arginine codons AGA and AGG. When high level bPL synthesis was induced in this strain, cell growth was inhibited and bPL accumulated to less than 10% of total cell protein. In addition, about 2% of the recombinant bPL produced from this strain exhibited an altered trypsin digestion pattern. Amino acid residues 74 through 109 normally produce 2 tryptic peptides, but the altered form of bPL lacked these two peptides and instead had a new peptide which was missing arginine residue 86 and one of the two flanking leucine residues. The codon for arginine residue 86 was AGG and the codons for the flanking leucine residues 85 and 87 were TTG. When 5 of the 9 AGA and AGG codons in the bPL structural gene were changed to more preferred arginine codons, cell growth was not inhibited and bPL accumulated to about 30% of total cell protein. When bPL was purified from this modified strain, which included changing the arginine codon at position 86 from AGG to CGT, none of the altered form of bPL was produced. These observations are consistent with a model in which translational pausing occurs at the arginine residue 86 AGG codon because the corresponding arginyl-tRNA species is reduced by the high level of bPL synthesis, and a translational hop occurs from the leucine residue 85 TTG codon to the leucine residue 87 TTG codon. This observation represents the first report of an error in protein synthesis due to an in-frame translational hop within an open reading frame.

Expression of human chorionic gonadotrophin alpha and beta subunits is depressed in trophoblast from pregnancies with early embryonic failure

The expression of the placental proteins human chorionic gonadotrophin alpha (HCG alpha), beta (HCG beta) and human placental lactogen (HPL) was examined in trophoblast from human normal pregnancy and early embryonic failure (EEF) using Northern blot analysis. Trophoblast from EEF expressed significantly depressed levels of HCG alpha (P < 0.05) and HCG beta (P < 0.01) when compared to normal pregnancy. Levels of expression of HPL in EEF were not significantly different to those from normal pregnancy. The gestational ages of the two groups were not significantly different. Immunocytochemistry on paraffin-fixed tissue sections supported these data and showed that mRNA levels reflected protein production of HCG within the tissue. It appears from these data that the depressed level of HCG found in the serum of women with early pregnancy failure is not solely a consequence of diminished placentation in these pregnancies, or placental necrosis, but that the genes of the alpha and beta HCG subunits are down-regulated. This study further suggests that there are two subsets of women with early pregnancy failure; those with apparently normal levels of placental proteins, and those with severely depressed levels. It would seem likely that these two groups have different aetiologies.

Human placental cells transformed with temperature-sensitive simian virus 40 are immortalized and mimic the phenotype of invasive cytotrophoblasts at both permissive and nonpermissive temperatures

Establishment of the human placenta is essential for subsequent development of the embryo. Previous studies from our laboratories have demonstrated that chorionic villus cytotrophoblast stem cells undergo a stepwise differentiation process in vivo that results in their ability to invade the uterine wall. This process can be mimicked by isolated primary first-trimester cytotrophoblasts in vitro. Efforts to study the regulation of this differentiation pathway have been hampered by the inability of the isolated cytotrophoblast to replicate in culture. We therefore performed experiments to determine the suitability of the temperature-sensitive simian virus 40-transformed cell line SPA 255-26 (SPA-26), derived from early-gestation cytotrophoblasts, for studying the cytotrophoblast differentiation pathway that results in uterine invasion. Our results show that this cell line exhibits many properties of differentiated early-gestation cytotrophoblasts at both permissive and nonpermissive temperature. These cells were invasive in vitro and expressed the repertoire of hormones, adhesion molecules, and proteinases characteristic of an advanced stage of cytotrophoblast differentiation in vivo. Thus, these cells should be useful in studying the regulation of the adhesive and invasive behavior of human cytotrophoblasts.

Ruminant placental lactogens: structure and biology

Ruminant placental lactogens (PL) are members of the somatotropin, prolactin gene family that are synthesized by trophectodermal binucleate cells. The structure and biology of PL has been studied in the cow, sheep, and goat. Ruminant PL have greater structural identity to prolactin than somatotropin, although they bind to both lactogenic and somatogenic receptors. The molecular weights of ovine and caprine PL are approximately 23,000, whereas bovine PL is larger (31,000 to 34,000) due to glycosylation. Placental lactogen is secreted into both the fetal and maternal circulations. The concentration of PL in the fetus decreases with advancing gestation, whereas PL concentration peaks in the maternal circulation during the last third of pregnancy then reaches a plateau. Furthermore, the maternal concentration of PL is 100- to 1,000-fold higher in sheep and goats than in cows. The precise factors that modulate secretion of PL are unknown, although placental mass and nutrition seem to play a role. Ruminant PL have both lactogenic and somatogenic biological activities and may also have unique activities mediated through a specific receptor. There is circumstantial evidence to suggest that PL plays a role in stimulating mammogenesis. Placental lactogen secreted into the fetal compartment may also help regulate fetal growth. Direct experimental data indicate that PL can regulate maternal intermediary metabolism. Thus, it may act as a partitioning agent to regulate nutrient supply for fetal growth. The precise biological function of PL in ruminants, therefore, still needs to be defined.

HPL-positive infiltrating trophoblastic cells in normal and abnormal pregnancy

In a series of 24 pregnant women, placental bed biopsies were performed in the third trimester at cesarean section. All the resulting specimens contained infiltrating trophoblast with both small and giant cells, and eight also contained vascular trophoblast. On immunoperoxidase staining for HPL, some small interstitial trophoblastic cells were positive in 12 cases. Some cells of the vascular intramural trophoblast and practically all cells of the vascular intraluminal trophoblast were positive. Seven cases were normal pregnancies whereas 17 were complicated by arterial hypertension and/or fetal growth retardation. A significant correlation between abnormal pregnancy and absence of HPL-positive interstitial cells in the placental bed biopsy was found. This probably indicates a diminished overall number of HPL-positive interstitial cells in the group of abnormal pregnancies and might reflect some defect of interstitial trophoblast. Such a defect may play a role in the arrest of the physiological changes of pregnancy in spiral arteries, which has been described in pre-eclampsia and in many cases of idiopathic fetal growth retardation.

Initiation of placental lactogen-I production by blastocysts growing on a two-dimensional surface and in hanging drops

The mouse blastocyst undergoes a program of protein secretion during the perimplantation period including the initial production of placental lactogen-I (mPL-I) on day 6 of pregnancy. Although blastocysts collected on day 5 also produce mPL-I when cultured to form outgrowths on plastic dishes, it was not known if embryos have an intrinsic ability to produce mPL-I during culture in vitro, or if a specific uterine influence is necessary. Earlier experiments also suggested that attachment of the trophoblast to a stable surface may be a prerequisite for synthesis of mPL-I. Both questions were addressed by examining mPL-I production by day 3 and day 4 embryos cultured either on a two-dimensional tissue culture dish surface or in hanging drops. The presence of intracellular mPL-I was assayed by immunohistochemistry, while the secreted hormone was detected by its known position in two-dimensional electrophoresis gels. These experiments demonstrated that these earlier stage embryos do have an intrinsic program for mPL-I production which proceeds in vitro under various culture conditions. Synthesis of mPL-I occurred in embryos suspended in hanging drops as well as in those spreading on a solid two-dimensional surface, thus showing that adhesion to a surface is not required for production of this hormone. Although some mPL-I synthesis was seen in embryos cultured in medium containing BSA as the sole macromolecule, the inclusion of fibronectin either in dishes, where it supports attachment, or in the hanging drop system stimulated mPL-I secretion. Serum supplementation in both culture systems further increased growth and differentiation of the embryo, as well as mPL-I secretion, compared to fibronectin supplementation.

Clinical counterpoint: the physiology of placental lactogen in human pregnancy

In summary, current evidence strongly suggests that PL may play a pivotal role during pregnancy, acting through distinct PL receptors to regulate and coordinate growth and metabolism in the mother and fetus. In early and midgestation, PL may be secreted preferentially into the fetal circulation, exerting growth-promoting effects at a time when the rate of linear growth of the fetus is maximal. Subsequently, during the latter half of pregnancy, the metabolic actions of PL in the mother and fetus may predominate, ensuring the optimal supply of nutrients to the fetus and utilization of the nutrients by fetal tissues. It therefore appears that PL affects fetal growth both by exerting effects on the fetus and the mother. Although hPL acts as "growth hormone of pregnancy," the regulation of the synthesis and secretion of hPL appears to be markedly different than that of GH.