Maternal Iron Deficiency Alters Trophoblast Differentiation and Placental Development in Rat Pregnancy.

Iron deficiency, which occurs when iron demands chronically exceed intake, is prevalent in pregnant women. Iron deficiency during pregnancy poses major risks for the baby, including fetal growth restriction and long-term health complications. The placenta serves as the interface between a pregnant mother and her baby, and it ensures adequate nutrient provisions for the fetus. Thus, maternal iron deficiency may impact fetal growth and development by altering placental function. We used a rat model of diet-induced iron deficiency to investigate changes in placental growth and development. Pregnant Sprague-Dawley rats were fed either a low-iron or iron-replete diet starting 2 weeks before mating. Compared with controls, both maternal and fetal hemoglobin were reduced in dams fed low-iron diets. Iron deficiency decreased fetal liver and body weight, but not brain, heart, or kidney weight. Placental weight was increased in iron deficiency, due primarily to expansion of the placental junctional zone. The stimulatory effect of iron deficiency on junctional zone development was recapitulated in vitro, as exposure of rat trophoblast stem cells to the iron chelator deferoxamine increased differentiation toward junctional zone trophoblast subtypes. Gene expression analysis revealed 464 transcripts changed at least 1.5-fold (P < 0.05) in placentas from iron-deficient dams, including altered expression of genes associated with oxygen transport and lipoprotein metabolism. Expression of genes associated with iron homeostasis was unchanged despite differences in levels of their encoded proteins. Our findings reveal robust changes in placentation during maternal iron deficiency, which could contribute to the increased risk of fetal distress in these pregnancies.

Vitamin D alleviates hypoxia/reoxygenation-induced injury of human trophoblast HTR-8 cells by activating autophagy.

INTRODUCTION: Attenuation of trophoblast cell dysfunction would be beneficial for retarding pre-eclampsia (PE). Vitamin D has been reported to improve trophoblast cell function in early PE, but the mechanism involved is not fully elucidated. This study is aimed to investigate whether vitamin D alleviates trophoblast cell dysfunction via regulating autophagy. METHODS: Human trophoblast HTR-8 cells were cultured in hypoxia/reoxygenation (H/R) condition to simulate the oxidative stress state of early PE in vitro. MTT, Transwell and tube formation assays were respectively applied to assess cell proliferation, invasion, and angiogenesis abilities. DCFH-DA staining was performed to detect cellular reactive oxygen species levels. GFP-RFP-LC3 plasmid transfection and transmission electron microscopy were subjected to monitor autophagy. Enzyme-linked immunosorbent assay and Western blot analysis were used to detect autophagy-related and pyroptosis-associated molecules. RESULTS: H/R led to severe impairments on the bio-function of HTR-8 cells, as evidenced by the deficiency of cell proliferation, invasion, and angiogenesis abilities, and the increase of cellular ROS production. Simultaneously, H/R inhibited autophagy and triggered pyroptosis. 1,25(OH)2D3, the hormonally active form of vitamin D, dramatically attenuated H/R-induced trophoblast dysfunction. Also, 1,25(OH)2D3 activated autophagy and inhibited pyroptosis. Additionally, autophagy-enhancer rapamycin exerted similar protective effect to that of 1,25(OH)2D3, whereas autophagy-inhibitor 3-methyladenine blocked the protective effect of 1,25(OH)2D3. DISCUSSION: The mechanism that vitamin D alleviates trophoblast cell dysfunction is associated with autophagy induction and pyroptosis inhibition.

Leptin and Nutrition in Gestational Diabetes.

Leptin is highly expressed in the placenta, mainly by trophoblastic cells, where it has an important autocrine trophic effect. Moreover, increased leptin levels are found in the most frequent pathology of pregnancy: gestational diabetes, where leptin may mediate the increased size of the placenta and the fetus, which becomes macrosomic. In fact, leptin mediates the increased protein synthesis, as observed in trophoblasts from gestational diabetic subjects. In addition, leptin seems to facilitate nutrients transport to the fetus in gestational diabetes by increasing the expression of the glycerol transporter aquaporin-9. The high plasma leptin levels found in gestational diabetes may be potentiated by leptin resistance at a central level, and obesity-associated inflammation plays a role in this leptin resistance. Therefore, the importance of anti-inflammatory nutrients to modify the pathology of pregnancy is clear. In fact, nutritional intervention is the first-line approach for the treatment of gestational diabetes mellitus. However, more nutritional intervention studies with nutraceuticals, such as polyphenols or polyunsaturated fatty acids, or nutritional supplementation with micronutrients or probiotics in pregnant women, are needed in order to achieve a high level of evidence. In this context, the Mediterranean diet has been recently found to reduce the risk of gestational diabetes in a multicenter randomized trial. This review will focus on the impact of maternal obesity on placental inflammation and nutrients transport, considering the mechanisms by which leptin may influence maternal and fetal health in this setting, as well as its role in pregnancy pathologies.

Gestational diabetes mellitus affects placental iron homeostasis: Mechanism and clinical implications.

Clinical studies suggest that pregnant women with elevated iron levels are more vulnerable to develop gestational diabetes mellitus (GDM), but the causes and underlying mechanisms are unknown. We hypothesized that hyperglycemia induces cellular stress responses leading to dysregulated placental iron homeostasis. Hence, we compared the expression of genes/proteins involved in iron homeostasis in placentae from GDM and healthy pregnancies (n = 11 each). RT-qPCR and LC-MS/MS analyses revealed differential regulation of iron transporters/receptors (DMT1/FPN1/ZIP8/TfR1), iron sensors (IRP1), iron regulators (HEPC), and iron oxidoreductases (HEPH/Zp). To identify the underlying mechanisms, we adapted BeWo trophoblast cells to normoglycemic (N), hyperglycemic (H), and hyperglycemic-hyperlipidemic (HL) conditions and assessed Fe3+ -uptake, expression patterns, and cellular pathways involving oxidative stress (OS), ER-stress, and autophagy. H and HL induced alterations in cellular morphology, differential iron transporter expression, and reduced Fe3+ -uptake confirming the impact of hyperglycemia on iron transport observed in GDM patients. Pathway analysis and rescue experiments indicated that dysregulated OS and disturbed autophagy processes contribute to the reduced placental iron transport under hyperglycemic conditions. These adaptations could represent a protective mechanism preventing the oxidative damage for both fetus and placenta caused by highly oxidative iron. In pregnancies with risk for GDM, antioxidant treatment, and controlled iron supplementation could help to balance placental OS levels protecting mother and fetus from impaired iron homeostasis.

YY1-PVT1 affects trophoblast invasion and adhesion by regulating mTOR pathway-mediated autophagy.

Insufficient trophoblast invasion is the key factor for the occurrence of recurrent spontaneous abortions (RSA). Our previous studies identified Yin Yang 1 (YY1) as a transcription factor involved in the regulation of trophoblast invasiveness at the maternal-fetal interface. Long noncoding RNAs (lncRNAs) can regulate gene expression and autophagy in many ways. The purpose of this study was to explore the relationship between YY1 and lncRNAs and the mechanism by which lncRNAs affect the biological behavior of trophoblasts. Bioinformatic analysis predicted that YY1 had three binding sites in the plasmacytoma variant translocation 1 (PVT1) promoter region. Chromatin immunoprecipitation experiments and electrophoretic mobility shift assays verified that YY1 can directly bind to the PVT1 promoter. Compared with its expression levels in human placental villi tissue samples from the normal pregnancy group, the PVT1 expression levels were significantly lower in tissues from the RSA group. PVT1 knockdown significantly reduced adhesion, invasion, autophagy, and mTOR expression in HTR-8/SVneo cells and greatly increased apoptosis in vitro. This study revealed a novel regulatory pathway in which YY1 can act directly on PVT1 promoter to regulate its transcription, which further affects trophoblast invasion and adhesion by regulating autophagy via the mTOR pathway, and these effects might be involved in RSA pathogenesis.

The YY1/MMP2 axis promotes trophoblast invasion at the maternal-fetal interface.

YY1 is a sequence-specific DNA-binding transcription factor that has many important biological roles. However, its function in trophoblasts at the maternal-fetal interface remains to be elucidated. In this study, we used an mRNA microarray and reverse transcription qPCR and compared the YY1 mRNA expression level in trophoblasts between patients with recurrent miscarriage (RM) and healthy control subjects. Our results revealed that YY1 mRNA expression was significantly lower in the trophoblasts of the RM group compared with the healthy control group. Furthermore, immunofluorescence and immunohistochemical data showed that YY1 was highly expressed in human placental villi during early pregnancy, especially in cytotrophoblast cells and invasive extravillous trophoblasts, and it was expressed at a much lower level in the placental villi of term pregnancy. YY1 overexpression enhanced, and knockdown repressed, the invasion and proliferation of trophoblasts. Antibody array screening revealed that YY1 significantly promoted MMP2 expression in trophoblasts. Bioinformatics analysis identified three YY1-binding sites in the MMP2 promoter region, and chromatin immunoprecipitation analysis verified that YY1 binds directly to its promoter region. Importantly, inhibition of YY1 by siRNA clearly decreased trophoblast invasion in an ex vivo explant culture model. Overall, our findings revealed a new regulatory pathway of YY1/MMP2 in trophoblast cell invasion during early pregnancy and indicated that YY1 may be involved in the pathogenesis of RM.

Effect of folic acid on human trophoblast health and function in vitro.

INTRODUCTION: The combined intake of folic acid (FA) from prenatal multivitamin supplements and fortified foods can result in FA intake values that exceed the tolerable upper intake level (UL). It is unclear what impact FA intake above the UL may have on the feto-placental unit. Our objective was to determine the effects of increasing concentrations of FA on trophoblast health and function in vitro. METHODS: Two human placental cell lines [HTR-8/SVneo (n = 5 experiments) and BeWo (n = 5 experiments)] and human placenta tissue explants (n = 6 experiments) were exposed to increasing concentrations of FA (2-2000 ng/mL) for 48-h. Intracellular total folate concentration, trophoblast proliferation, viability, apoptosis, placenta cell invasion and ß-hCG hormone release were assessed. RESULTS: Exposure to increasing FA concentrations resulted in higher intracellular total folate in placental cell lines and tissue explants (p < 0.05); yet, only minimal effects of excess folic acid were observed on the primary indicators of placental health and function studied. Specifically, treatment with excess folic acid (2000 ng/mL) resulted in reduced cellular viability in the villous trophoblast BeWo cell line and increased rates of proliferation in the HT8-8/SVneo extravillous trophoblast cell line (p < 0.05). Further, deficient concentrations of folic acid (2 ng/mL) resulted in decreased cell viability and invasive capabilities of the HTR-8/SVneo extravillous trophoblast cell line (p < 0.05). DISCUSSION: Our results demonstrate that placental health and function may be compromised in conditions of folate deficiency, and not necessarily in conditions of excess FA. This finding supports the recommendation of prenatal folic acid supplementation in the North American population. Further work aimed at clarifying the therapeutic window of FA intake in the obstetrical population is warranted.

Choline inadequacy impairs trophoblast function and vascularization in cultured human placental trophoblasts.

Maternal choline intake during gestation may influence placental function and fetal health outcomes. Specifically, we previously showed that supplemental choline reduced placental and maternal circulating concentrations of the anti-angiogenic factor, fms-like tyrosine kinase-1 (sFLT1), in pregnant women as well as sFLT1 production in cultured human trophoblasts. The current study aimed to quantify the effect of choline on a wider array of biomarkers related to trophoblast function and to elucidate possible mechanisms. Immortalized HTR-8/SVneo trophoblasts were cultured in different choline concentrations (8, 13, and 28 µM [control]) for 96-h and markers of angiogenesis, inflammation, apoptosis, and blood vessel formation were examined. Choline insufficiency altered the angiogenic profile, impaired in vitro angiogenesis, increased inflammation, induced apoptosis, increased oxidative stress, and yielded greater levels of protein kinase C (PKC) isoforms δ and ϵ possibly through increases in the PKC activators 1-stearoyl-2-arachidonoyl-sn-glycerol and 1-stearoyl-2-docosahexaenoyl-sn-glycerol. Notably, the addition of a PKC inhibitor normalized angiogenesis and apoptosis, and partially rescued the aberrant gene expression profile. Together these results suggest that choline inadequacy may contribute to placental dysfunction and the development of disorders related to placental insufficiency by activating PKC.

Iodide transporters expression in early human invasive trophoblast.

CONTEXT: The placenta plays an essential role in the fetomaternal exchanges of iodine and thyroid hormones. Propylthiouracil (PTU) is presently considered to be the treatment of choice for hyperthyroidism during the first trimester of pregnancy. Little is known on the expression of iodide transporters in invasive human trophoblast and the possible effect of PTU on this early phase of human placental development. OBJECTIVE: To analyze during early pregnancy expression of sodium/iodide symporter (NIS) and pendrin at the feto-maternal interface in situ in first trimester placentas, in vitro during human trophoblastic cell differentiation in presence or not of PTU. DESIGN: NIS and pendrin immunodetection were performed on 8-10 WG placental tissue sections and in primary cultures of first trimester placenta trophoblastic cells, which differentiate in vitro into syncytiotrophoblast or invasive extravillous cytotrophoblasts (EVCT). The effect of PTU (1 mM) was tested in EVCT on iodide transporters expression, cell invasion, and hCG secretion. RESULTS: NIS and pendrin were present in early human trophoblast at the maternofetal interface. Their expression was modulated with in vitro trophoblast differentiation. Early invasive EVCT were characterized by higher expression of NIS than pendrin. In vitro PTU did modify significantly neither EVCT iodide transporters expression nor EVCT biological functions: i.e. invasive properties and hCG secretion. CONCLUSION: This study reveals that NIS is highly expressed in early human trophoblast at the feto-maternal interface. PTU has no effect on early human trophoblast invasion.

MicroRNA-155 inhibits proliferation and migration of human extravillous trophoblast derived HTR-8/SVneo cells via down-regulating cyclin D1.

MiR-155 is known to participate in various cellular processes by targeting gene expression. We previously revealed a link between miR-155 and perturbation of trophoblast invasion and differentiation. This study aimed to investigate the target molecule(s) of miR-155 on the influence on the proliferation and migration of trophoblast cells. Bioinformatics analysis showed that, at the 3' untranslated region (UTR) of cyclin D1, six bases are complementary to the seed region of miR-155. Luciferase assays and cyclin D1 3'UTR transfection assays validated that cyclin D1 3'UTR was the target of miR-155 in HTR-8/SVneo cells. Overexpression of miR-155 in HTR-8/SVneo cells reduced the level of cyclin D1 protein, decreased cell proliferation and invasion, and increased cell number at the G1 stage. Furthermore, the increased expression of miR-155 also regulated the protein levels of kinase inhibitory protein p27 and phosphorylated cytoskeletal protein filamin A. In conclusion, we found that cyclin D1 may be a target of miR-155 in HTR-8/SVneo cells, and demonstrated a negative regulatory role of miR-155 involved in cyclin D1/p27 pathway in proliferation and migration of the cells.

Possible roles for folic acid in the regulation of trophoblast invasion and placental development in normal early human pregnancy.

In addition to its role in the prevention of neural tube defects, folic acid has many other physiological functions, including cell proliferation, DNA replication, and antioxidant protection. The aim of this study was to determine the role that folic acid has in regulating placental trophoblast development. Placental explants from placentae at gestational age 7 wk (n = 3) were cultured in folic acid at concentrations of 10(-6) M, 10(-8) M, and 10(-10) M. Extravillous trophoblast (EVT) invasion was assessed following 6-day culture, and explants were used for immunohistochemical evaluation of proliferation (MKI67) and apoptosis (active caspase 3). In addition, an array was performed on cell culture supernatants to examine a range of matrix metalloproteinases (MMPs) and tissue inhibitors of MMPs (TIMPs). Folic acid increased the invasion of EVT cells in this explant model by between 83% and 19% (P = 0.005), and this was associated with increased MKI67 positivity and decreased active caspase 3 positivity; this effect was concentration dependent and showed a biphasic response. In addition, culture in folic acid increased vascular density, as determined by anti-CD31 immunostaining (P = 0.05). The increase in EVT invasion correlated with increased placental explant secretion of MMP2 (P = 0.01), MMP3 (P = 0.01), and MMP9 (P = 0.02). This study demonstrates that folic acid is potentially important in a number of crucial early stages of placental development, including EVT invasion, angiogenesis, and secretion of MMPs, and highlights the need for further studies to address the benefit of longer-term folic acid supplementation throughout pregnancy to prevent pregnancy disorders associated with deficient placental development, including preeclampsia.

Inhibition of cell invasion and protease activity by cholesterol sulfate.

We demonstrated that cholesterol sulfate (CS) inhibits invasion of a trophoblast cell line and plasmin enzyme activity in a noncompetitive manner by binding to the enzyme itself, suggesting that CS can repress cell invasion by inhibiting proteinases such as those involved in the plasminogen activator/plasmin system. Considering these results, it is possible that CS may act as a signaling molecule between the trophoblast and endometrium, and may regulate the process of implantation.

Discovery of novel regulatory peptides by reverse pharmacology: spotlight on chemerin and the RF-amide peptides metastin and QRFP.

Reverse pharmacology is a screening technology that matches G protein-coupled receptors (GPCRs) with unknown cognate ligands in cell-based screening assays by detection of agonist-induced signaling pathways. One decade spent pursuing orphan GPCR screening by this technique assigned over 30 ligand/receptor pairs and revealed previously known or novel undescribed ligands, mostly of a peptidic nature. In this review, we describe the discovery, characterization of the structural composition, biological function, physiological role and therapeutic potential of three recently identified peptidic ligands. These are metastin, QRFP in a context of five RF-amide genes described in humans and the chemoattractant, chemerin. Metastin was initially characterized as a metastasis inhibitor. Investigations using ligand/receptor pairing revealed that metastin was involved in a variety of physiological processes, including endocrine function during pregnancy and gonad development. The novel RF-amide QRFP is implicated in food intake and aldosterone release from the adrenal cortex in the rat. Chemerin, first described as TIG2, is upregulated in tazarotene-treated psoriatic skin. By GPCR screening, bioactive chemerin was isolated from ovarial carcinoma fluid as well as hemofiltrate. Characterization as a chemoattractant for immature dendritic cells and analysis of the expression profile of metastin and its receptor suggested a physiological role of chemerin as a mediator of the immune response, inflammatory processes and bone development.

The role of thyroid hormone in trophoblast function, early pregnancy maintenance, and fetal neurodevelopment.

OBJECTIVE: To review the literature on the roles of thyroid hormone in trophoblast function, early pregnancy maintenance, and fetal neurodevelopment. METHODS: MEDLINE was searched for English-language papers published from 1971 to 2003, using the key words "brain," "hypothyroidism," "placenta," "pregnancy," "threatened abortion," "thyroid hormone," "thyroid hormone receptor," "thyroid hormone replacement therapy," "thyroid hormone-responsive gene," and "trophoblast." RESULTS: Transplacental transfer of thyroid hormone occurs before the onset of fetal thyroid hormone secretion. Thyroid hormone receptors and iodothyronine deiodinases are present in the placenta and the fetal central nervous system early in pregnancy, and thyroid hormone plays a crucial role both in trophoblast function and fetal neurodevelopment. Maternal hypothyroxinemia is associated with a high rate of spontaneous abortion and long-term neuropsychological deficits in children born of hypothyroid mothers. Maternal iodine deficiency also causes a wide spectrum of neuropsychological disorders in children, ranging from subclinical deficits in cognitive motor and auditory functions to hypothyroid-induced cognitive impairment in infants. However, these conditions are preventable when iodine supplementation is initiated before the second trimester. Although thyroid hormone replacement therapy is effective for reducing the adverse effects complicated by maternal hypothyroidism, the appropriate dose of thyroid hormone is mandatory in protecting the early stage of pregnancy. CONCLUSIONS: Close monitoring of maternal thyroid hormone status and ensuring adequate maternal thyroid hormone levels in early pregnancy are of great importance to prevent miscarriage and neuropsychological deficits in infants.

Maternal recognition of pregnancy.

Enhanced secretion of PGF2 alpha from endometrial explants in vitro in response to oxytocin is associated with augmented activities of phospholipase A2, phospholipase C and prostaglandin endoperoxide H synthase (PGS). In early pregnancy, maintenance of the corpus luteum is associated with an absence of pulsatile PGF2 alpha secretion; an increase in endometrial inhibitors of phospholipase A2 and PGS contribute to the antiluteolytic alterations of PGF2 alpha secretion. Linoleic acid is a competitive inhibitor of arachidonic acid metabolism by PGS, and microsomal concentrations of free linoleic acid are increased in the endometrium of pregnant cattle. The trophoblast produces large quantities of interferon tau (IFN-tau). Inhibition of increases in endometrial oestradiol receptor mRNA and protein are associated with intrauterine administration of recombinant (r) ovine (o) IFN-tau in sheep. Intrauterine injections of ovine (b) IFN-tau in cattle (days 14-17) altered endometrial function so that secretion of PGF2 alpha from cultured endometrial epithelial cells was reduced. Antiluteolytic effects were not expressed in 20% of cows receiving IFN-tau or rbIFN-alpha I1 indicating that an inadequate endometrial responsiveness may contribute to embryo mortality. IFN-tau may activate a signal transduction system similar to that induced by other type I IFNs; activation of an intracellular tyrosine kinase ultimately leads to activation of an IFN-stimulated response element to induce gene transcription. Biological responses associated with pregnancy and IFN-tau treatment are integrated into a multifactorial antiluteolytic model. Strategies to enhance embryo survival could include supplementation with rIFN-tau and alterations in endometrial responsiveness to this cytokine through dietary manipulation of lipid metabolism.

Neem oil inhibits two-cell embryo development and trophectoderm attachment and proliferation in vitro.

PURPOSE: The in vitro effect of neem oil was studied on the development of mouse two-cell embryos and trophectodermal cell attachment and proliferation. METHOD: Female mice were primed with gonadotropins for superovulation and caged with male mice. Early embryos, at the two-cell and the blastocyst stages, were recovered at 40 and 88 hr post-hCG from the oviducts and the uteri, respectively. In the first experiment, two-cell embryos were exposed to culture medium containing different concentrations of neem oil for 1, 12, and 24 hr and then grown in neem oil-free culture medium and assessed for the formation of total and hatching blastocysts at 96 hr. In the second experiment, partially hatching blastocysts were cocultured with human endometrial stromal cell monolayers in culture medium containing different concentrations of neem oil and assessed for the attachment and proliferation of trophectodermal cells at 96 hr. RESULTS: Exposure of two-cell embryos to neem oil concentrations of 0.050-0.500% for 1 hr, 0.010-0.250% for 12 hr, and 0.005-0.100% for 24 hr caused significant inhibition of the formation of total and hatching blastocysts, in a dose-dependent manner. Neem oil at 0.050-0.100% concentrations inhibited, in a dose-dependent manner, the in vitro attachment and proliferation of trophectodermal cells of partially hatching blastocysts cocultured with human endometrial stromal cells monolayers. CONCLUSION: Neem oil inhibits the development of two-cell embryos and attachment and proliferation of the trophectodermal cells of partially hatching blastocysts in vitro. The study encourages the use of this herbal product as a postcoital contraceptive that warrants further research.

Human trophoblast cultures: models for implantation and peri-implantation toxicology.

Implantation is the process that leads from blastocyst attachment to its embedding in the uterine wall. It is widely believed that failure of implantation is a common cause of pregnancy loss. Toxic agents can interfere directly with the process of implantation and therefore may account for unexplained implantation failures. Our knowledge of human implantation remains limited, mainly due to the lack of adequate experimental models. Studies of mechanisms underlying implantation in humans are by nature and for ethical reasons restricted to in vitro models. The aim of this review is to provide a critical evaluation of various in vitro models of implantation in humans, as well as essential background knowledge required for application of these models to the assessment of peri-implantation toxicity. Particular attention has been devoted to cell-cell and cell-matrix interactions as possible endpoints in the screening of toxic agents.

Expression of cellular oncogenes in teratoma-derived cell lines.

The expression of ten proto-oncogenes was studied in cell lines derived from transplantable mouse teratomas. The cell lines represent different forms of early embryonic cell specialization. The analysis included two embryonal carcinoma (EC) lines (PCC3 and F9), and four differentiated cell lines derived from teratocarcinoma, namely trophoblastoma (3-TDM), parietal endoderm (PYS-2), visceral endoderm (PSA5-E) and skeletal myoblasts (Cl10). The expression of c-oncogenes was studied by analysing poly(A)+RNA for complementary sequences by dot blot and Northern blot hybridization. The results were related to the rate of cell multiplication and the state of differentiation by examining [3H]thymidine incorporation, growth curves and tissue-specific differentiation markers. Expression of c-myc and c-Ki-ras was found in all cell lines. In dot blot assays, poly(A)+RNA from all cell lines also hybridized with v-abl and v-sis probes. A marked decrease in c-myc expression was found in teratoma-derived myoblasts differentiating into myotubes. A similar reduction was found when 'nullipotent' F9 cells were induced by retinoic acid (RA) to form primitive endoderm. However, reduction of the growth rates of the parietal and visceral endodermal cell lines were not accompanied by decreased expression of c-myc or c-Ki-ras. Hybridization signals obtained with a v-sis probe was low in all teratoma-derived cell lines tested, except for the myogenic cell line Cl10. Both in exponentially growing and differentiated cultures of this line, two size classes of transcripts hybridized strongly to the v-sis probe. However, these transcripts, 7 and 3 kb, most likely represent endogenous retroviral transcripts and not c-sis transcripts. Expression of c-myb, c-mos, c-fes, c-src and c-erb A and c-erb B could not be detected in any of the cell lines studied.

Protein synthetic requirements for the outgrowth of trophoblast cells from mouse blastocysts.

Mouse blastocysts cultured under optimal conditions attach to the surface of the culture dish and subsequently give rise to outgrowths of trophoblast cells. The migration of trophoblast cells appears to be analogous to their behavior during the invasive phase of implantation in utero. In these studies, we have attempted to determine the time of synthesis and nature of the products required for trophoblast outgrowth. Fourth-day blastocysts were cultured in two different media: cNCTC, a nutrient medium supplemented with fetal calf serum, and PCMF, a simple preimplantation medium lacking amino acids and serum. Trophoblast outgrowth occurs in the former, but not in the latter, medium. Most blastocysts will give rise to outgrowths following as little as 12 hr of exposure to cNCTC at the appropriate time, even if they are subsequently placed in PCMF. Outgrowth fails to occur if blastocysts are treated with cycloheximide during the interval of exposure to cNCTC, whereas treatment with the antimetabolite after the period of culture in cNCTC does not block outgrowth. These observations are consistent with the view that protein(s) essential for trophoblast outgrowth are synthesized many hours prior to the actual event.

Activation of 'delayed implanting' mouse embryos in vitro.

Blastocysts were recovered from mice with experimentally produced delay of implantation. The dormant embryos were incubated in vitro for up to 24 h in medium containing [3H]uridine and supplemented with mouse serum or bovine serum albumin. Outgrowth of the trophoblast cells occurred in the presence of serum but not with bovine serum albumin. In contrast, the rate of incorporation of [3H]uridine into RNA by the embryos increased steadily throughout the period of incubation and was not influenced by the presence of serum. The change in incorporation of [3H]uridine was due to an increase in the overall rate of RNA synthesis and serum therefore has not effect on this aspect of embryo activation. The observation that a stimulatory serum factor is necessary for outgrowth of dormant embryos in vitro, but is not required for increased metabolic activity, indicates that these two aspects of embryo activation are regulated differently in vivo. With the assumption that trophoblast outgrowth and the changes in metabolic activity in vitro are analogous to the events that occur when embryonic diapause is terminated in vivo, it is suggested that the process of embryo activation after delayed implantation proceeds in a stepwise fashion with each phase being controlled in different ways.