Expression of c-onc genes: c-fos transcripts accumulate to high levels during development of mouse placenta, yolk sac and amnion

The Role of Fe, Zn, and Cu in Pregnancy

Iron (Fe), copper (Cu), and zinc (Zn) are microelements essential for the proper functioning of living organisms. These elements participatein many processes, including cellular metabolism and antioxidant and anti-inflammatory defenses, and also influence enzyme activity, regulate gene expression, and take part in protein synthesis. Fe, Cu, and Zn have a significant impact on the health of pregnant women and in the development of the fetus, as well as on the health of the newborn. A proper concentration of these elements in the body of women during pregnancy reduces the risk of complications such as anemia, induced hypertension, low birth weight, preeclampsia, and postnatal complications. The interactions between Fe, Cu, and Zn influence their availability due to their similar physicochemical properties. This most often occurs during intestinal absorption, where metal ions compete for binding sites with transport compounds. Additionally, the relationships between these ions have a great influence on the course of reactions in the tissues, as well as on their excretion, which can be stimulated or delayed. This review aims to summarize reports on the influence of Fe, Cu, and Zn on the course of single and multiple pregnancies, and to discuss the interdependencies and mechanisms occurring between Fe, Cu, and Zn.

Placental iron transport: The mechanism and regulatory circuits

As the interface between the fetal and maternal circulation, the placenta facilitates both nutrient and waste exchange for the developing fetus. Iron is essential for healthy pregnancy, and transport of iron across the placenta is required for fetal growth and development. Perturbation of this transfer can lead to adverse pregnancy outcomes. Despite its importance, our understanding of how a large amount of iron is transported across placental membranes, how this process is regulated, and which iron transporter proteins function in different placental cells remains rudimentary. Mechanistic studies in mouse models, including placenta-specific deletion or overexpression of iron-related proteins will be essential to make progress. This review summarizes our current understanding about iron transport across the syncytiotrophoblast under physiological conditions and identifies areas for further investigation.

Comparative Expression and Distribution of c-fos, Estrogen Receptorα (ERα), and p38α in the Uterus of Rats, Monkeys, and Humans

The uterine cellular expression and distribution of c-fos, ERα and p38α was compared in humans, nonhuman primates, and rats using immunohistochemistry. ERα and c-fos were present in the glandular (GE) and luminal epithelial cells (LE) of humans and nonhuman primates, with differing expression patterns evident between proliferative and secretory cycle phases. In rats, the highest and lowest expression of c-fos was present during proestrus and estrus, respectively, in the LE and GE. The most intense ERα staining in rats was observed during proestrus in the GE, while the least intense staining was seen in the LE during proestrus. Strong LE and GE expression of p38α as present in rats in all stages of the estrous cycle and during the proliferative phase in both humans and nonhuman primates. No p38α expression was observed during the secretory phase in either humans or nonhuman primates. Our work suggests that c- fos, ERα and p38α (a) are primarily expressed during the proliferative phase, but not the secretory phase and exhibit interspecies expression variability, and (b) rats exhibit cyclic changes in the expression of c- fos and ERα.

Detection of fetomaternal genotype associations in early-onset disorders: evaluation of different methods and their application to childhood leukemia

Several designs and analytical approaches have been proposed to dissect offspring from maternal genetic contributions to early-onset diseases. However, lack of parental controls halts the direct verification of the assumption of mating symmetry (MS) required to assess maternally-mediated effects. In this study, we used simulations to investigate the performance of existing methods under mating asymmetry (MA) when parents of controls are missing. Our results show that the log-linear, likelihood-based framework using a case-triad/case-control hybrid design provides valid tests for maternal genetic effects even under MA. Using this approach, we examined fetomaternal associations between 29 SNPs in 12 cell-cycle genes and childhood pre-B acute lymphoblastic leukemia (ALL). We identified putative fetomaternal effects at loci CDKN2A rs36228834 (P = .017) and CDKN2B rs36229158 (P = .022) that modulate the risk of childhood ALL. These data further corroborate the importance of the mother's genotype on the susceptibility to early-onset diseases.

The colony-stimulating factor-1 receptor is a specific marker of macrophages from the bony fish gilthead seabream

We report the molecular cloning of the colony-stimulating factor-1 receptor gene from the bony fish gilthead seabream (sbCSF-1R). The deduced sbCSF-1R shows a predicted signal sequence, a transmembrane domain and a tyrosine kinase domain, all in conserved positions. A transcript showing a premature stop codon that predicted the removal of 84 C-terminal amino acids was also found. RT-PCR expression studies demonstrate that, although the sbCSF-1R transcripts are found in different immune tissues, including gill, liver, spleen, blood, peritoneal exudate, thymus and head-kidney (HK), their expression is confined to the monocyte/macrophage lineage. Furthermore, the expression of sbCSF-1R might be modulated by the activation stage of the macrophages, since both the infection of fish and the in vitro activation of leukocytes resulted in the down-regulation of gene expression. These data indicate that the CSF-1R may be used as a specific probe for cells of the monocyte/macrophage lineage in the gilthead seabream, an immunological tractable fish model. In addition, the functional characterisation of the CSF-1R and its ligand may shed light into the mechanisms of proliferation and the pathways of differentiation of macrophages in bony fish.

The murine placenta contains hematopoietic stem cells within the vascular labyrinth region

In the midgestation murine embryo, several major vascular tissues contain hematopoietic stem cell (HSC) activity. These include the aorta-gonad-mesonephros region (AGM), yolk sac, and fetal liver. Recently, the placenta was demonstrated to harbor hematopoietic progenitors, but it was not examined for HSC activity. We demonstrate here that the placenta also harbors adult-repopulating HSCs. Placental HSCs begin to be detected at embryonic day (E) 11, and HSC numbers increase dramatically between E11 and E12, exceeding the numbers in the circulating embryonic blood. Furthermore, all placental HSC activity is restricted to the GFP+ fraction of cells in Ly-6A (Sca-1) GFP transgenic embryos. Cells coexpressing GFP and endothelial markers CD34 and CD31 are found in the embryonic vasculature of the placental labyrinth. Moreover, placental cell expression of other HSC markers and transcription factors suggests that HSC emergence may occur in the placenta, as has been proposed for other embryonic hematopoietic sites.

Placental vascularisation requires the AP-1 component fra1

Fra1 is an immediate-early gene encoding a member of the AP-1 transcription factor family, which has diverse roles in development and oncogenesis. To determine the function of Fra1 in mouse development, the gene was inactivated by gene targeting. Foetuses lacking Fra1 were severely growth retarded and died between E10.0 and E10.5, owing to defects in extra-embryonic tissues. The placental labyrinth layer, where X-gal staining revealed expression of Fra1, was reduced in size and largely avascular, owing to a marked decrease in the number of vascular endothelial cells, as shown by the lack of Flk1 expression. In contrast, the spongiotrophoblast layer was unaffected and expressed the marker genes 4311 (Tpbp) and Flt1. Furthermore, mutant foetuses exhibited yolk-sac defects that may contribute to their growth retardation and lethality. Importantly, when the placental defect was rescued by injection of Fra1(−)(/)(−) ES cells into tetraploid wild-type blastocysts, Fra1(−)(/)(−) pups were obtained that were no longer growth retarded and survived up to 2 days after birth without apparent phenotypic defects. These data indicate that a defect in the extra-embryonic compartment is causal to the observed lethality, and suggest that Fra1 plays a crucial role in establishing normal vascularisation of the placenta.

SHORT COMMUNICATION maternal thyroid dysfunction and c- fos and c- jun expression in rat placenta

Maternal thyroid dysfunction is associated with perturbed fetal brain development and neurological deficits in adulthood in rat and human. To investigate whether these effects occur secondary to placental dysfunction, c- fos and c- jun expression in placenta from normal (euthyroid) and moderately hypothyroid rat dams were investigated by Northern hybridization analysis. In normal placenta, c- fos expression increased by 74 per cent between 16 and 21 days of gestation (dg) whereas c- jun expression declined by 46 per cent. Moderate maternal hypothyroidism depressed placental c- fos expression by 32 per cent at 19 dg, but elevated c- fos and c- jun expression by 139 and 86 per cent, respectively, at 21 dg. Maternal hypothyroidism may therefore induce c- fos/c- jun -related placental dysfunction, but only relatively late in gestation when fetal thyroid function is already established.

Transcription factor AP-1, and the role of Fra-2

Transcription factors function to regulate gene transcription. They may be constitutively expressed or may only be activated during specific situations. Activator protein-1 (AP-1) is an inducible transcription factor, and is comprised of multiple protein complexes that include the gene products of the fos and jun gene families. Numerous cellular and viral genes contain AP-1 binding sites within their promoters and, accordingly, AP-1 has been shown to play a role in the regulation of both basal and inducible transcription of these genes. fos-related antigen-2 (fra-2) has been found to have both similar and unique properties to that of other fos gene members in terms of its regulation and expression. The analysis and determination of the function of Fra-2 will provide further information on the role of AP-1.

Estrogen induces expression of c-fos and c-jun via activation of protein kinase C in an endometrial cancer cell line and fibroblasts derived from human uterine endometrium

Endometrial fibroblasts derived from uterine endometrium as controls and endometrial cancer cell lines (Ishikawa and HHUA cells) were analyzed for the induction manner of c-fos and c-jun transcripts in endometrial cancers, some of which are estrogen-dependent in growth. Estrogen increased c-fos expression and protein kinase C (PKC) activity in fibroblasts and Ishikawa cells, but not in HHUA cells. Progesterone diminished c-fos and c-jun expression and PKC activity induced by estradiol in the fibroblasts, but not in Ishikawa cells, which persistently overexpressed c-fos and c-jun. In these cells, 12-0-tetra-decanoylphorbol-13-acetate (TPA) increased c-fos and c-jun expression as did estradiol. Pretreatment with 1-(5-isoquinolinesulfonyl)-2-methylpiperazine dihydrochloride (H-7) abolished estrogen-inducible over-expression of c-fos and c-jun. The combination of both estradiol and TPA at maximum effective concentration exerted no additive and synergistic effect on induction of c-fos and c-jun expression. In conclusion, persistent activation of PKC might lead to overexpression of c-fos and c-jun in some endometrial cancers with an estrogen predominant milieu, which might be, at least in part, associated with the transformation or growth potential.

Expression of c-Fos in subcutaneous adipose tissue of the fetal pig

Subcutaneous adipose tissue from fetal pigs was examined for c-Fos expression in developing adipocytes. Enhanced c-Fos expression was found in the nuclei of adipocytes and cells closely associated with fat cell clusters from 75 and 105 day old fetuses. 50 day old fetuses which had no adipocytes showed no enhanced c-Fos expression in undifferentiated cells. c-Fos expression in adipocytes was not transient, but persisted through the gestational period from 75 to 105 days. The timing of c-Fos induction appears to be closely related to adipocyte differentiation and was found only in developing adipocytes and cells closely associated with fat cell cluster and was not found in independent stromal-vascular cells.

Expression of proto-oncogenes in mouse eggs and preimplantation embryos

The expression of several protooncogenes has been investigated in mouse eggs and preimplantation embryos using reverse transcription coupled to amplification of cDNAs by the polymerase chain reaction (RT-PCR). The genes chosen for analysis included both cytoplasmic (c-raf-1, rasH, rasK, and rasN) and nuclear (c-fos and c-myc) proto-oncogenes encoding proteins involved in the transduction of signals from protein-tyrosine kinase growth factor receptors. Transcripts of the cytoplasmic proto-oncogenes were detected both as maternal and embryonic mRNAs at levels (ca. 1,000 copies per egg or embryo) approximately comparable to their levels of transcription in somatic cells. Transcripts of c-fos and c-myc were also detected in both eggs and embryos, although at more variable levels: Maternal transcripts were present at very low levels (ca. 1-10 copies per egg) in growing oocytes and ovulated eggs; embryonic transcription of c-myc increased, reaching mRNA levels of approximately 100-1,000 copies per embryo in four-cell embryos, morula, and blastocysts; in contrast the transcription of c-fos remained at low, barely detectable levels throughout preimplantation development. Although the significance of the low levels of c-fos mRNA is unclear, these results indicate that preimplantation embryos possess the basic intracellular signaling apparatus required to respond to polypeptide growth factors.

Regulated expression of intrinsic factor-cobalamin receptor by rat visceral yolk sac and placental membranes

Intrinsic factor-cobalamin receptor (IFCR) activity in visceral yolk sac and placental membranes is regulated during pregnancy in rats. While the IFCR activity declined in the visceral yolk sac membranes by 15-fold, it rose nearly 20-fold in the placental membranes from fourteen to nineteen days of gestation. The visceral yolk sac membranes revealed a 230 kDa protein that co-migrated with pure rat renal IFCR. This 230 kDa band was also identified as IFCR in both the membranes by immunoblotting with anti-serum to rat renal IFCR. Immunoprecipitation of 35S labeled proteins obtained from in vitro translation using visceral yolk sac mRNA from 14-day pregnant rats, yielded on SDS-PAGE a single band of 220 kDa, while those obtained from 19-day pregnant rats did not. The binding of intrinsic factor-cyano[57Co]cobalamin complex to the visceral yolk sac membranes was inhibited by preincubation of these membranes with anti-serum to rat IFCR but not with anti-serum to rat asialoglycoprotein receptor or mannose or mannan or N-acetylglucosamine. Based on these results, we suggest that the IFCR activity, protein expression and mRNA levels in fetal membranes are regulated during pregnancy and may play an important role in the maternal-fetal transfer of cobalamin.

Bone morphogenetic proteins (BMP-2 and BMP-3) induce the late phase expression of the proto-oncogene c-fos in murine osteoblastic MC3T3-E1 cells

Here we report that bone morphogenetic proteins 2 and 3 (BMP-2 and BMP-3) induced marked expression of c-fos mRNA in a biphasic manner, i.e. the late phase (48 to 60 h) as well as the immediate-early phase (0.5 h), in murine osteoblastic MC3T3-E1 cells in vitro. The BMP-induced late phase c-fos gene expression was temporally associated with the onset of marked expression of the genes for osteocalcin and alkaline phosphatase, differentiation markers of mature osteoblasts. In contrast, none of TGF-beta 1, 10% FBS, IGF-I and IGF-II, which induced only the immediate-early c-fos mRNA expression, stimulated the expression of osteocalcin and alkaline phosphatase genes. These data suggest that in osteoblasts BMP-2 and BMP-3 induce the late phase expression of c-fos, which may play a role in transcriptional activation of the genes involved in differentiation of osteoblasts.

Expression of nerve growth factor and nerve growth factor receptor genes in human tissues and in prostatic adenocarcinoma cell lines

Nerve growth factor (NGF) mRNAs were detected and quantified in a variety of normal and neoplastic human tissues by northern blot hybridization. Human heart contained the highest NGF mRNA levels, whereas lower but comparable levels were found in the placenta, prostate, and kidney. All tissues examined coexpressed the low-affinity NGF receptor (LNGFR), whereas none of these tissues expressed the high-affinity NGF receptor encoded by the trk protooncogene. The widespread distribution of the LNGFR suggests that it plays a role in the regulation of normal cell growth. No overexpression of NGF or LNGFR mRNA was detected in neoplastic tissues, whereas LNGFR-like immunoreactivity was localized outside of tumor cells. Transforming growth factor-alpha and protooncogene c-fos expression in these tissues did not show a systematic correlation with NGF/LNGFR expression. Furthermore, regulation of the human NGF gene was studied in DU145 cells, a prostatic adenocarcinoma cell line that synthesizes significant NGF mRNA levels. Serum induced, whereas dexamethasone inhibited, NGF mRNA synthesis in these cells. Serum induction was preceded by a rapid and transient activation of the c-fos protooncogene.

Expression of c-fos and c-jun mRNA in the developing chicken lens: relationship to cell proliferation, quiescence, and differentiation

The in vivo developmental pattern of c-fos and c-jun mRNA expression has been examined in the embryonic chicken lens using a coupled reverse transcription/polymerase chain reaction assay. Levels of each mRNA were measured in the central epithelium, equatorial epithelium, and fiber cell mass at 6, 10, 14, and 19 days of development. The results showed that c-fos and c-jun mRNAs accumulated during development of the embryonic chicken lens epithelium as the proportion of proliferating cells decreased, suggesting that quiescent epithelial cells express high levels of both protooncogene mRNAs. Cells in the early stages of terminal differentiation near the lens equator also contained relatively high levels of c-fos and c-jun mRNA. As lens fiber cells matured, the number of copies of c-fos mRNA per cell decreased markedly, while c-jun mRNA increased. These findings demonstrate that c-fos and c-jun are differentially regulated during terminal differentiation of lens fiber cells and suggest that these protooncogenes are expressed in lens epithelial cells following cell cycle arrest.

Growth factors in the uterus: steroidal regulation and biological actions

Rapid progress has been made within the last 5-6 years in characterizing polypeptide growth factors in uterine tissues and fluids. There is convincing evidence that their synthesis and/or secretion is regulated by steroid hormones. The possibility that these growth factors play a central role in growth and development of the uterus or placenta is suggested by the presence of their receptors on uterine or placental cells and their stimulatory effects on these cells in vitro. Since growth factors interact synergistically and also have non-mitogenic functions, the presence of a variety of these factors in the uterus suggests that they probably regulate various aspects of uterine function through complex autocrine and paracine pathways. However, experimental models need to be designed that will permit a more detailed analysis of the actual role of these factors in utero. Fruitful approaches may be to administer neutralizing antibodies or blocking peptides so as to antagonize uterine growth factor action, or to develop appropriate transgenic animals. These and other lines of study should help us to understand the role of growth factors in development of the immature uterus, growth of the placenta or gravid uterus, repair and angiogenesis of the endometrium, and uterine pathology.

C-jun and jun-B oncogene expression during placental development

During embryogenesis, growth and differentiation occur in a sequential, predetermined order suggesting that specific genes are turned on and off in a precise and well-regulated manner. Placental development, which is characterized by massive proliferation and differentiation of multiple cell types, must be similarly regulated. Early response protooncogenes, such as c-jun and jun-B, have been associated with both proliferation and differentiation of different cell types. In this study, using Northern blot analysis, we found that c-jun and jun-B expression occurred in human placentas throughout gestation. Maximal expression of c-jun occurred in early gestation, and maximal expression of jun-B occurred in late gestation. We speculate that peak expression of c-jun in human placenta at early gestation may be related to cytotrophoblastic proliferation and that peak expression of jun-B in late gestation may be related to further terminal differentiation of trophoblastic cells.

The transcription factor, Egr-1, is rapidly modulated in response to retinoic acid in P19 embryonal carcinoma cells

The pluripotent murine embryonal carcinoma cell line, P19, differentiates along at least three main pathways under the inductive influence of retinoic acid (RA). The events most critical to the establishment of a particular differentiation pathway must occur early since P19 cells are committed to differentiation pathways after 30 min of exposure to RA (M. W. McBurney, personal communication and our unpublished results). We have, therefore, looked for genes that are induced (or repressed) within 30 min of RA addition and find that Egr-1 is one of these genes. Egr-1 is a transcription factor of the zinc-finger class and is known to transactivate genes after binding to specific oligonucleotide sequences. We describe here the extremely rapid and transient increase of Egr-1 transcript and protein levels in P19 cells after RA addition. Stable induction of Egr-1 transcripts occurred in the presence of protein synthesis inhibitors. Simultaneous addition of RA and cycloheximide did not result in an additive effect. The mechanism of induction with either drug appears to involve relief of a block to transcriptional elongation. The response was more rapid at high RA concentrations and this suggests that the Egr-1 transcription factor could play a role in initiation of differentiation pathways of P19 EC cells.

Genetic regulation of salivary proteins in rodents

The presence of a protein in the cell is the result of a complex pathway that is known by the term gene expression. In this article we review the existing literature on the structure and expression of representative salivary gland genes and their regulated expression during development and upon extracellular stimulation. The expression of one of the "nuclear" protooncogenes, c-fos, in rat parotid glands is also discussed. Finally, we present some suggestions for future studies that will help to understand the mechanisms leading to gene regulation in rat salivary glands.

Stage and tissue-specific expression of fosB during mouse development

The product of the fos-related fosB gene shares many properties with c-Fos such as inducibility by growth factors, complex formation with members of the Jun family and cooperative binding with Jun to the TPA response element (TRE). To investigate whether in contrast to these functional similarities, the two genes might be differentially regulated, we have analysed the expression of fosB during mouse development by in situ hybridization. A spatially restricted accumulation of fosB mRNA in the visceral yolk sac and the nervous system was observed during late gestation. The highest levels of fosB mRNA were found in the cortex and the dorsal columns of the spinal cord. Moreover, stage-specific expression was seen in sensory organs such as retina and vibrissae, where the levels of fosB RNA either increased (retina) or decreased (vibrissae) between days 15 and 18. Our results suggest that fosB may have a specific function in the development of ectoderm-derived tissues. Expression of fosB during prenatal development differs markedly from the known expression pattern of c-fos, pointing to different tissue-specific functions for c-fos and fosB.

Transferrin receptor expression in early postimplantation mouse trophoblast and associated tissues

The expression of the transferrin receptor (TR) was examined on murine trophoblast cells on days 6, 8 and 10 of gestation, using a monoclonal antibody visualized by indirect immunofluorescence on cryostat sections of the implant site. In the day 6 tissues, TR were observed on both the ectoplacental cone (EPC) and mural giant cell trophoblast populations, as well as on the embryonic ectoderm, anti-mesometrial decidual cells, uterine glandular epithelium and myometrium. By the 8th day of gestation, TR expression was weak, or undetectable on trophoblast giant cells (TGC), but remained strong on the proliferating cells of the EPC and embryo. In the definitive placenta (day 10), TR are expressed primarily on the differentiated labyrinthine trophoblast cells involved in the maternal-fetal transfer of iron.

EGF receptor activities in mammalian development

The receptor for epidermal growth factor (EGF) and its analog transforming growth factor alpha (TGF alpha) is ubiquitous, implying quite general roles for EGF/TGF alpha in cell viability and tissue maintenance in adult tissues. There is also evidence that the EGF receptor is active in promoting wound healing and tissue regeneration in adult organs, such as skin, liver, and intestinal epithelium. It is likely that EGF receptors have more specific roles during the gestation period. For example, we have detected EGF receptors on the 3.5-day blastocyst (trophectoderm) surface and since TGF alpha-like mRNA sequences and peptides have been detected at this time (Rappolee et al., Science 241:1823, 1988), there is a strong implication for autocrine stimulation in pre- and peri-implantation stage embryos. Paracrine stimulation between the embryo and maternal tissues is also likely since both receptors and TGF alpha are present in decidual cells. Therefore EGF receptors may take part in growth regulation of the early embryo and in the process of implantation. Other examples where EGF receptors may play specific roles during embryonic development are discussed.

Protein synthesis in embryonic tissues during mouse postimplantation development

Mouse embryos of the NMRI strain between the 7th and 9th day of gestation were isolated from the uterus and dissected into the various tissue derivatives in order to investigate newly synthesized proteins during morphogenesis. The day 7 embryo was fragmented into trophoblast and ectoplacental cone, distal and proximal endoderm, extraembryonic and embryonic ectoderm. The day 8 and day 9 embryos were divided into trophoblast and placental anlage, yolk sac, amnion, and allantois, as well as cranial, central, and caudal embryonic tissue. The intact embryos were incubated in Dulbecco's minimum essential medium in the presence of 35S-methionine for 4 h, then dissected into the various fragments, and further processed for two-dimensional gel electrophoresis. Protein synthesis of the isolated tissue derivatives was analyzed and compared for the three developmental stages. Concerning the proteins with isoelectric points in the range of 4.5 to 8.0 and molecular weight ratio (M(r)) values between 20,000 and 200,000, we found several significant quantitative and qualitative differences in the various tissue fragments. In addition, we observed further quantitative and qualitative differences in protein synthesis during the postimplantation period investigated. We propose that the differences reflect some of the cell lineage- and developmental stage-specific changes in gene expression during early mammalian differentiation.

c-fos proto-oncogene expression in astrocytes associated with differentiation or proliferation but not depolarization

Expression of the c-fos proto-oncogene in rat neocortical astrocytes in culture was examined using Northern blotting and immunocytochemistry. Marked induction of c-fos mRNA in astrocytes was observed after treatment with epidermal growth factor (EGF), basic fibroblast growth factor (bFGF), dibutyryl cyclic AMP (db-cAMP), and phorbol diester (TPA; 12-O-tetra-decanoylphorbol 13-acetate), which are known to induce the proliferation or differentiation of astrocytes. Increase of c-fos protein immunoreactivity (IR) was obtained after treatment with fetal calf serum, EGF, bFGF, db-cAMP and TPA. High concentrations of calcium ionophore A23187, which were lethal to cultured astrocytes, also increased c-fos protein-IR. Treatment with lower concentrations of calcium ionophore (which slightly increase Ca2+ uptake), high K+ and nerve growth factor had no detectable effect on c-fos expression. These results show that depolarization does not induce c-fos in astrocytes and suggest that c-fos may play a role in differentiation and proliferation of astrocytes.

High levels of c-fos proto-oncogene expression in normal human adult skin

The proto-oncogene c-fos is thought to play an important role in the modulation of cell growth and differentiation. In normal tissues that have been studied to date, c-fos expression has been found to be regulated in a tissue-specific manner. Actually, little is known about its expression in normal human adult skin (NHAS). Moreover, the epidermis is a useful tissue to study the role of cellular oncogenes because keratinocytes can be observed simultaneously in their proliferative as well as differentiated state. We studied c-fos expression in NHAS using different molecular approaches which permit us to characterize and localize c-fos products within the epidermis, specifically, at the RNA level by Northern blot and in situ hybridization, and at the protein level by immunofluorescence and Western blotting. Here, we show that both c-fos mRNA and protein are present at high levels in NHAS. These results contrast with the low level of c-fos expression reported for most human adult tissues. Furthermore, c-fos expression is visible throughout the epidermal layers indicating that it is not restricted to proliferating basal cells. The epidermis, therefore, represents the first human adult tissue where c-fos is expressed at high levels in vivo and provides an interesting model to further elucidate the role of this proto-oncogene in normal and pathologic conditions.

Repression of c-fos transcription is mediated through p67SRF bound to the SRE

Human c-fos expression is subject to tight transcriptional control. The gene is expressed at a high, constitutive level in some cell types and at a very low, but rapidly inducible level in many others. Induction of transcription by serum growth factors is mediated by the serum response element (SRE) to which at least two transcription factors, p67SRF and p62, bind. In this paper it is demonstrated that the low basal level of transcription is mediated through p67SRF bound to the SRE and that high, constitutive expression is observed when binding is prohibited. In this situation, an AP-1 consensus binding site adjacent to the SRE permits transactivation of the gene. Thus three levels of c-fos expression, induced, repressed and constitutive, appear to be determined by occupation of the SRE by p67SRF and its interaction with other proteins.

Localization of mRNA for the oncotrophoblastic protein oncomodulin during implantation and early placentation in the rat

The mRNA for the oncodevelopmental calcium-binding protein oncomodulin (MW 11,700) has been detected in tissues of the rat conceptus by in situ hybridization using biotinylated RNA probes. Oncomodulin mRNA was detected in the basal zone and labyrinth of rat placenta, following a similar distribution to that shown for oncomodulin by immunohistochemistry. Oncomodulin mRNA was also detected in rat ectoplacental cone at ten days and in amnion and PYS, but not VYS from 11 days onward. Previously oncomodulin was not detected embryonically from day 14 to birth, but in the present study of oncomodulin mRNA and protein, both were detected in implantation stages from blastula through egg cylinder. Staining was also present on decidual tissue. The suggestion is made that the oncomodulin gene is initially active in all cell types, but later its activity is confined to extraembryonic tissues.

Localization of molecules with restricted patterns of expression in morphogenesis: an immunohistochemical approach

In a search for molecules with restricted patterns of expression during development, monoclonal antibodies were raised against different transitory structures of the chick embryo. Mice were immunized with cell suspensions from lightly homogenized embryonic tissues explanted from morphogenetically active regions. A convenient immunohistochemical assay was used to screen the hybridoma supernatants on a large scale. It relied on the use of poly(ethylene glycol) as embedding medium. Its water miscibility allowed, in a one-step incubation with antibody-containing supernatants, the dewaxing and rehydration of the tissue sections as well as antibody binding. We report here the usefulness of this approach in selecting monoclonals with unique patterns of immunoreactivity. In this study, cephalic neural crest cells in early or late phase of migration, together with their surrounding tissues, were used as immunogens. The monoclonal antibodies obtained have been classified into regional, cell-lineage, cell-cycle or extracellular material-associated markers. The information provided by the direct visualization of the immunoreactivity of the various monoclonal antibodies on tissue sections, as early as the first round of screening, allows rapid determination of the subsequent strategy to be followed for further characterization of the individual markers.

Detection of fos oncogene products by monoclonal antibody FO-120 in lymphoproliferative disorders

We investigated the expression of fos oncogene proteins in lymphoproliferative disorders, using a monoclonal antibody (FO-120) that was prepared against a synthetic oligopeptide of fos protein (amino acid sequence from 127 to 152). Although peripheral blood leukocytes were rarely positive for FO-120, they were transiently stained after lectin (PHA) stimulation. After culture with IL-2 for 1 or 2 weeks, less than 40% of the lymphocytes weakly reacted with FO-120, whereas strongly positive cells were detected in more than 70% of cells in half the T-cell lines established from preleukemic state of adult T-cell leukemia (pre-ATL) and all of ATL derived T-cell lines. All in vivo specimens of non-Hodgkin's malignant lymphomas, except for one case of T-cell lymphoma were also strongly positive. In addition, the extent of the antibody reactivity correlated with the histopathological grade of malignancy in B-cell lymphoma. The reactivity to most AILD-IBL lesions overlapped with that to T-lymphomas, and could be distinguished from that to reactive lesions. FO-120 appears to be a useful tool for detecting early neoplastic changes in lymphoproliferative disorders.

Persistent and enhanced expression of c-fos gene products in various kinds of human hematopoietic cell lines. Immunofluorescence study using prepared monoclonal antibodies

Two kinds of monoclonal antibodies recognizing fos proto-oncogene (c-fos) products were prepared using a synthetic oligopeptide corresponding to amino acids 127-152 of the fos oncogene products. These monoclonal antibodies (FO-120 & FO-145) detected fos gene products induced in a human monocyte cell line (U-937) by phorbol acetate (TPA) and induced in both human and mouse fibroblast cell lines (284, BALB/c 3T3) by serum-stimulation. One of the monoclonal antibodies (FO-120) reacted with 50-kDa and 42-kDa proteins and the other antibody (FO-145) reacted with a 30-33-kDa protein. The expression of the fos gene in various human hematopoietic cell lines was investigated using these prepared monoclonal antibodies. While almost all hematopoietic cell lines tested reacted with these monoclonal antibodies to various degrees, the majority of normal peripheral blood lymphocytes cultured with lectin (PHA) and interleukin 2 (IL-2) did not, suggesting that cells of some permanent hematopoietic cell lines, irrespective of their lineage specificity and growth factor dependency, continuously express the fos oncogene. These monoclonal antibodies may be useful for detecting early neoplastic changes in hematopoietic cells.

Active ras and myc oncogenes can be compatible, but Sv40 large T antigen is specifically suppressed with normal differentiation of mouse embryonic stem cells

The pathobiological effects of oncogenes on normal differentiation of mouse embryonic stem cells from 4-day embryos were examined by introducing active ras, myc, and SV40 large T genes, all driven by mouse metallothionein I enhancer and promoter. Stem cell clones R5, M3, and T2 for ras, myc, and SV40 T genes, respectively, were particularly chosen for analyses because of their higher levels of transgene expression and their diploid chromosomal constitutions. These stem cells were then introduced into host 4-day embryos and the embryos were allowed to develop in the uterus of foster mothers. The stem cells colonized the tissues as extensively as the parent cells and gave rise to adult chimera with no apparent loss or abnormality of the embryos. The active ras and myc oncogenes introduced were expressed not only in the stem cells, but also in the developing embryos and in a variety of tissues of adult chimeras. However, although T antigen was originally expressed in the stem cells, it was not expressed in either developing embryos or tissues of adult chimeras. Induced by retinoic acid treatment in vitro or by subcutaneous grafting, this suppression of T-gene expression was also confirmed in differentiated progeny cells from several stem cell clones expressing T antigen. Permanent lines of fibroblast-like cells could be established at higher frequency from primary cultures of tissues of chimera, subcutaneous differentiated cells, and in vitro differentiated cells derived from T2 cells, and all these clones reexpressed T antigen. The results suggest that active myc and ras genes can be compatible with normal differentiation of the stem cells, but the expression of T antigen is specifically suppressed with recognition of its coding domain.

Expression of c-fos antisense RNA inhibits the differentiation of F9 cells to parietal endoderm

To test the putative role of c-fos in F9 differentiation, we have attempted to inhibit c-fos expression in these cells using an SV40-based expression vector (pSVneo-sof) that programs expression of c-fos antisense (sof) sequences as a 3' extension of a neo mRNA transcript. Of six G418-resistant clones isolated in transfection experiments, five expressed neo-sof transcripts. Two clones synthesized polyadenylated mRNA of the expected size (3.8 kb), two were smaller than expected, and one was larger. Two clones that expressed reduced levels of c-fos protein were inhibited in the induction of laminin, type IV collagen, and proteoglycan-19 RNA transcripts measured after 4 days of differentiation induction with RA and dibutyryl cyclic AMP. Also inhibited was the induction of the differentiation markers, TROMA-1 and TROMA-3. Antisense-expressing cells were not inhibited in the differentiation pathway to visceral endoderm since the alpha-fetoprotein gene was activated normally. We conclude that c-fos antisense expression inhibits some aspects of differentiation in F9 cells.

Mediastinal germ cell tumors and histiocytosis

Two cases of mediastinal germ cell tumors associated with primary hemoproliferative disorders are reported. The first case was a 23-year-old man who presented simultaneously with a mediastinal immature teratoma with focal yolk sac differentiation and a cytologically benign histiocytic proliferation associated with refractory thrombocytopenia. In the second case, an unsuspected mediastinal immature teratoma with focal yolk sac and hepatic differentiation was found postmortem in a 33-year-old man who had died of fulminant malignant histiocytosis. Although the histiocytosis in the former case failed to fulfill all the usual diagnostic criteria of malignant histiocytosis, both cases probably represent different manifestations of the same pathologic process. Review of the 19 published cases of hematologic malignancies associated with mediastinal germ cell tumors and of related experimental studies suggests a role for yolk sac differentiation in the pathogenesis of this syndrome.

Expression of a murine homeobox gene precedes the induction of c-fos during mesodermal differentiation of P19 teratocarcinoma cells

The controlled expression of regulatory genes is the basis of normal mouse embryo development. Recent studies in our laboratory have revealed temporally and spatially restricted expression of homeobox-containing genes and the cellular protooncogene c-fos in developing mouse embryos. In order to gain insight into cellular control mechanisms responsible for differential expression of these potential regulatory genes during developmental processes, we set out to analyze their expression in teratocarcinoma cells as an in vitro model system for cellular differentiation. We demonstrated that the homeobox-containing gene Hox 1.3 and the c-fos protooncogene are expressed in P19 teratocarcinoma cells prior to their terminal myogenic differentiation, which is indicated by the expression of muscle-specific myosin. Using a combination of the transcriptional run-on assay and Northern analysis, we defined some of the cellular control mechanisms that are responsible for the changes in transcription pattern during P19 differentiation. The development-dependent activation of c-fos and muscle-specific myosin mRNA was found to result from an increased transcription rate. In contrast, the primary induction of Hox 1.1 (m6)-specific mRNA was controlled on the posttranscriptional level by changes in the half-life of the transcript. In addition, in situ hybridization studies revealed a characteristic spatially restricted expression of Hox 1.1 RNA in P19 aggregates, which may point to an important role of cell-cell interactions for Hox 1.1 expression in the mesodermal muscle differentiation pathway.

Oncogene expression in differentiating F9 mouse embryonal carcinoma cells

Differentiation of F9 mouse embryonal carcinoma cells in culture is accompanied by a decrease in growth rate and loss of tumorigenicity. Cells differentiating in monolayer culture (to parietal endoderm-type cells) or in aggregates (to visceral endoderm-type cells) show qualitatively similar changes in transcript levels from several c-oncogenes. In contrast with other studies with F9 cells, we find an early decrease in c-myb RNA but not in c-myc RNA. This and a later increase in c-src RNA may be associated with decreasing cell growth rate. Before differentiation, induction and maintenance of elevated c-abl RNA levels depend on the presence of retinoic acid in the medium. After differentiation c-abl RNA levels decline only partially when retinoic acid is removed. Increased RNA from c-fos is seen late in differentiation in monolayer cultures only, a change also seen with appearance of similar endoderm cell types in the developing mouse embryo.

Establishment of a rat placental cell line expressing characteristics of extraembryonic membranes

A cell line was derived from midgestation chorioallantoic placental explants of the outbred Holtzman rat. The cell line was found to express characteristics of extraembryonic membranes and to grow when introduced into allogeneic hosts. Growth in allogeneic hosts was detected following intraperitoneal injection of the cells but not following subcutaneous injection. The transplanted cells grew as cystic structures free in the peritoneum and as solid masses adhered to various abdominal organs. Cystic structures had a homogeneous morphology consisting of an epithelial-like cell layer surrounding a fluid-filled sac. Solid masses had a heterogeneous morphology, containing parts resembling normal components of the extraembryonic membranes (trophoblast, parietal, and visceral yolk sacs). Biochemical analysis of the placenta-derived cell line and transplanted structures derived from the cell line indicated that the cells had the potential to produce a variety of proteins characteristic of extraembryonic tissues. Cultured cells and both types of in vivo transplants produced the basement membrane protein, laminin. Peritoneal cystic structures also contained alpha-fetoprotein mRNA and very high levels of c-fos mRNA. Solid masses demonstrated elevated alkaline phosphatase activity, a marker of trophoblast cells. Cells grown in vitro expressed elevated c-myc mRNA levels, whereas, c-myc mRNA levels were reduced in the in vivo transplants. The behavior of the cell line in vitro and following in vivo transplantation suggests it contains elements capable of differentiation toward various components of the extraembryonic membranes. The results indicate that the rat placental cell line will be valuable for future studies on the differentiation of trophoblast cells and other components of the extraembryonic membranes.

Expression of the proto-oncogene int-1 is restricted to specific neural cells in the developing mouse embryo

We have used in situ hybridization and computer-aided reconstruction to study the spatial distribution of expression of the mammary tumor proto-oncogene int-1 during mouse embryogenesis. int-1 RNA accumulation is restricted to specific regions of the neural plate and its derivatives between 9 and 14.5 days of development. int-1 RNA accumulates throughout the neural plate at the anterior head folds of the 9 day embryo but only at its lateral tips in more posterior regions. Following neural tube closure, int-1 expression is restricted to specific regions of the dorsal wall of the brain ventricles and spinal cord, the ventral wall of the midbrain and the diencephalon, and the lateral walls of the neuroepithelium at the midbrain-hindbrain junction. These data suggest that int-1 has a role in the early stages of central nervous system development in the mouse embryo.

The molecular genetics of nervous system tumors

Major insights have resulted in the last few years from the application of the techniques of molecular genetics to problems of development, differentiation, growth control, and neoplasia. It is now recognized that these problems are often actually different facets of the central question: how are genes regulated under various circumstances? These problems are of particular interest to neurosurgeons insofar as they relate to the mechanisms of development and differentiation of the nervous system and its tumors. This review attempts to provide an introduction to the salient issues and to the current state of knowledge in these various fields in order to promote an understanding of nervous system neoplasia and of areas that bear potential importance for research and therapy.

Suppression of tumorigenicity in somatic cell hybrids does not involve quantitative changes in transcription of cellular Ha-ras, Ki-ras, myc, and fos oncogenes

The transcriptional activity of ten cellular oncogenes was analyzed in somatic cell hybrids that had been obtained after fusion of tumorigenic Chinese hamster cells and normal mouse fibroblasts. The hybrids showed either the tumorigenic or the nontumorigenic phenotype (suppression of tumorigenicity). Out of ten c-onc genes analyzed, four (c-Ha-ras, c-Ki-ras, c-myc, and c-fos) were found to be transcriptionally active at similar levels in tumorigenic as well as in nontumorigenic (suppressed) hybrids. Thus we conclude that suppression of tumorigenicity in Chinese hamster X mouse somatic cell hybrids does not correlate with quantitative changes in expression of these cellular oncogenes. The remaining six cellular oncogenes (c-abl, c-erb A and B, c-fes, c-myb, and c-sis) were not transcriptionally active in these hybrids.

Possible role of c-fos, c-N-ras and c-mos proto-oncogenes in muscular development

Time course analyses of various proto-oncogene transcripts compared with cytoskeleton-specific and muscle-specific messenger RNAs (mRNAs) were carried out during growth and differentiation of a clonal line of rat myoblasts that retain the capacity to form non-contractile fibres in vitro. Throughout their growth phase, these cells express consistent levels of c-fos, c-myc, c-Ki-ras and c-N-ras RNA and no c-mos RNA. When the cultures approach confluency the level of c-fos RNA rises sharply 3-4-fold, peaks, and rapidly declines when muscle-specific transcripts start accumulating, to become negligible in myotube-forming cells. These changes occur whatever the concentration in seric factors. By contrast, the level of c-N-ras RNA rises up to 3-fold and both c-myc and c-Ki-ras RNAs are slowly eliminated during the myogenic process, whereas no c-mos RNA is detectable. However, skeletal muscles from prenatal fetuses and adult animals were reproducibly found to contain both low and high levels of c-mos RNA respectively. These data and the demonstration that inactivation of the c-fos gene correlates with the loss of myogenic capability in six lines of neoplastic myoblasts, including four lines transformed by the v-fos oncogene, suggest a physiological function for this proto-oncogene during early stages of myogenesis and for the c-N-ras and c-mos genes in later stages of muscular development.