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Biomedical subjects

N de Groot

Publications and source records attributed to N de Groot.

At least 55 records · Page 3Linked to original sources
PubMed1994

Relaxation of imprinting in trophoblastic disease.

Genomic imprinting--the uniparental-dependent transmittance of a genetic trait--has been accepted in recent years as a major mechanism in mammalian genetics. We studied the expression of the H19 gene, a parentally imprinted (maternally expressed) gene, by in situ hybridization in human placenta and trophoblastic disease. Expression was found to be abundant, in a decreasing order, in the intermediate trophoblast (villous and interstitial), the cytotrophoblast, and the syncytiotrophoblast. The villous stroma was also prominently labeled. Partial hydatidiform mole showed a similar pattern of expression as normal placenta. As expected, complete hydatidiform mole, whose genome consists of two haploid sets of paternal origin, was not labeled in the villous stroma and surrounding trophoblastic layer. However, some of the large mononuclear cells in the proliferating groups sprouting from the villous surface were strongly labeled. Prominent expression of H19 was found in placental site trophoblastic tumor and gestational choriocarcinoma. The phenomenon of emergence of expression of alleles subject to repression according to their gamete of origin is termed relaxation of imprinting, and is considered to be relevant to tumorigenesis. We suggest that the expression of the maternally expressed H19 gene in the androgenetic tissue of complete hydatidiform mole represents relaxation of imprinting and may be associated with its malignant potential.

Choriocarcinoma↗
PubMed1994

A growing relationship between genomic imprinting and tumorigenesis.

The association between aberrations of the human genome and the development of cancer is well established. Gene imprinting, defined as gene expression based on the gamete of origin, has previously been shown to be involved in this process by the loss of tumor suppressor gene regulation. We suggest that the activation of imprinted proto-oncogenes and growth factors may also play a vital role in tumorigenesis. Mechanistically, this can occur when the gene is removed from its imprinted sequence area, thus escaping repression. Synteny between the human and mouse genome provides the opportunity for targeted studies of imprinted genes suspected to be involved in cancer.

Animals↗
PubMed1994

The RAD7 and RAD16 genes, which are essential for pyrimidine dimer removal from the silent mating type loci, are also required for repair of the nontranscribed strand of an active gene in Saccharomyces cerevisiae.

The rad16 mutant of Saccharomyces cerevisiae was previously shown to be impaired in removal of UV-induced pyrimidine dimers from the silent mating-type loci (D. D. Bang, R. A. Verhage, N. Goosen, J. Brouwer, and P. van de Putte, Nucleic Acids Res. 20:3925-3931, 1992). Here we show that rad7 as well as rad7 rad16 double mutants have the same repair phenotype, indicating that the RAD7 and RAD16 gene products might operate in the same nucleotide excision repair subpathway. Dimer removal from the genome overall is essentially incomplete in these mutants, leaving about 20 to 30% of the DNA unrepaired. Repair analysis of the transcribed RPB2 gene shows that the nontranscribed strand is not repaired at all in rad7 and rad16 mutants, whereas the transcribed strand is repaired in these mutants at a fast rate similar to that in RAD+ cells. When the results obtained with the RPB2 gene can be generalized, the RAD7 and RAD16 proteins not only are essential for repair of silenced regions but also function in repair of nontranscribed strands of active genes in S. cerevisiae. The phenotype of rad7 and rad16 mutants closely resembles that of human xeroderma pigmentosum complementation group C (XP-C) cells, suggesting that RAD7 and RAD16 in S. cerevisiae function in the same pathway as the XPC gene in human cells. RAD4, which on the basis of sequence homology has been proposed to be the yeast XPC counterpart, seems to be involved in repair of both inactive and active yeast DNA, challenging the hypothesis that RAD4 and XPC are functional homologs.

Adenosine Triphosphatases↗
PubMed1994

Human imprinted genes as oncodevelopmental markers.

Imprinted genes mediate unique maternal or paternal genetic roles and their function is essential in prenatal development. The reciprocally imprinted human insulin-like growth factor 2 (IGF2) and H19 genes are expressed during embryonal life, also in the placenta, and are downregulated postnatally. They reexpress in pediatric tumors (e.g. Wilms' tumor) and in inborn developmental syndromes predisposing to such tumors (e.g., Beckwith-Wiedemann syndrome). H19 (RNA transcripts) and IGF2 are manifested in Wilms' tumor, rhabdomyosarcoma, immature ovarian teratoma and gestational trophoblastic diseases. We have found that in the placenta and in urothelial carcinoma, H19 expression reflects the degree of invasiveness. These genes, displaying a tissue-specific oncofetal pattern of expression, are, therefore, tumor markers.

Beckwith-Wiedemann Syndrome↗
PubMed1994

Parallel regulation of parentally imprinted H19 and insulin-like growth factor-II genes in cultured human fetal adrenal cells.

Adjacent, parentally imprinted, insulin-like growth factor-II (IGF-II) and H19 genes are highly expressed during embryogenesis and are important for fetal growth. Human fetal adrenals express abundantly both IGF-II and H19 genes. To clarify the significance and regulation of the H19 gene, we studied its expression in fetal adrenals. In situ hybridization experiments showed H19 RNA expression throughout the fetal adrenal cortex, with slightly higher expression in the outer definitive (adult) than in the inner fetal zone. In primary cultures of fetal adrenal cells, ACTH and other activators of the protein kinase-A signal transduction pathway increased both H19 and IGF-II RNA accumulation 1.7- to 10-fold. Staurosporine, a protein kinase-C inhibitor, increased H19 and IGF-II RNA to the same extent as did ACTH. The protein kinase-C activator 12-O-tetradecanoyl phorbol-13-acetate and cytokines, tumor necrosis factor-alpha and interferon-gamma, inhibited H19 and IGF-II RNA accumulation. Transforming growth factor-beta 1 caused a decrease in levels of H19 and IGF-II RNA, whereas the IGFs caused a slight increase. Our data show parallel multifactorial regulation of H19 and IGF-II RNAs in human fetal adrenal cells. This suggests common regulatory mechanisms for these adjacent genes.

Adrenal Cortex↗
PubMed1994

Ultrastructural characteristics of cytotrophoblast cells during stages of differentiation.

Isolated cytotrophoblast cells from term human placenta were separated into eleven fractions according to cell size, by centrifugal elutriation. Each fraction isolated was examined by electron microscopy to elucidate ultrastructural features consistent with differences in stages of cellular differentiation. As a rule, increasing cell size correlated with evidence of progressive intracellular differentiation. This was represented by the appearance of specialization structures in later fractions, and by changes in the density of organelles and other cellular constituents. Progressive development and maturation of the rough endoplasmic reticulum was also evident. These data are the first to demonstrate successful subfractionation of the heterogeneous cytotrophoblast cell population into distinct groups, each representing different levels of cellular differentiation. These morphologic features of differentiation correlate closely with established biochemical parameters associated with various stages of intermediate cytotrophoblast cell differentiation.

Cell Differentiation↗
PubMed1993

Use of a novel system for defining a gene imprinting region.

Gene imprinting involves the expression of a single allele, depending on its parental origin. In this report, we describe the use of a novel system, implementing human tissues exclusively endowed with either maternally or paternally inherited chromosomes, to better define a known gene imprinting region. Specific RNA transcripts for Placental Ribonuclease Inhibitor (PRI) and Cathepsin D were analysed by northern blotting for expression in complete hydatidiform mole, mature teratoma, and normal placenta. These genes are in close proximity to the reciprocally imprinted H19 and IGF-2 genes found on chromosome 11p15.5. Since all the tissues studied expressed Cathepsin D and PRI, these are not, by definition, imprinted, but as yet we cannot define the borders of the imprinting area on chromosome 11p15.5.

Alleles↗
PubMed1993

Intermediate cells during cytotrophoblast differentiation in vitro.

Differentiation of the human placental trophoblast cell involves a multistep process, with the generation of several distinct types of intermediate cytotrophoblast cells. Using a short term in vitro cell culture system and centrifugal elutriation, we studied the isolation and morphological and biochemical differentiation of these separated intermediate cell populations. Freshly isolated cell fractions, incubated for 24 h, are heterogeneous in their differentiation stages as determined by the secretion of the proteins chorionic gonadotropin alpha and beta, human placental lactogen, and pregnancy specific beta 1-glycoprotein. Maintenance in cell culture allows for the further differentiation of these intermediate cells and for syncytium formation. With the use of sequential trypsinizations, our data also suggest the parallel differentiation of cytotrophoblast cells into two distinct subsets: one which, through differentiation, gets committed to syncytium formation, and the other, which remains mononuclear despite high degrees of biochemical differentiation. These latter cells retain the capacity for syncytium formation when reintroduced into appropriate culture conditions. These findings refine the use of the term "intermediate cell" by previous investigators. We suggest that our in vitro system defines normal intermediate stages of trophoblast differentiation, and also serves as a model to simulate adverse conditions of syncytial degeneration or injury.

Cell Differentiation↗
PubMed1992

Parental imprinting of the human H19 gene.

It has only recently become clear that genetic imprinting plays an important role in human embryogenesis and in processes leading to the development of pediatric cancers and other human diseases. Using a unique human tissue, the androgenetic complete hydatidiform mole, we established that the maternally inherited allele of the imprinted H19 gene is expressed. Our results also show that the paternal allele of the human IGF-II gene, a gene suspected to be parentally imprinted in humans, is expressed.

Blotting, Northern↗
PubMed1992

Differentiation of choriocarcinoma cell line (JAr).

Choriocarcinoma, a highly malignant tumor arising from the trophoblast, comprises a heterogenous population of cells including cytotrophoblasts, intermediate trophoblasts, and syncytiotrophoblasts. In order to investigate trophoblast differentiation, we used centrifugal elutriation to separate cells from the JAr choriocarcinoma cell line according to their size and to further show that the resultant cell populations differ in their stage of differentiation. Two % of the cell population consists of large, multinuclear cells, which display the highest level of chorionic gonadotropin (CG) mRNAs. The increase in the CG beta mRNA with cell size is a consequence of the transcriptional mechanism, since agents which induce differentiation in JAr cells, i.e., methotrexate, increase the level of CG alpha and CG beta transcripts, cause a shift in cell size, and result in the formation of multinuclear cells. The multinuclear cells in the JAr population arise, at least partly, from kariokinesis without cytokinesis.

Cell Differentiation↗
PubMed1986

Alkaline phosphatase and protein kinase(s) activities in free cytoplasmic mRNPs from human term placenta.

Free mRNPs isolated from human term placental tissue were examined for protein kinase and phosphoprotein-phosphatase activities. Free mRNPs incubated with [gamma-32P]ATP in a protein kinase standard buffer show self-phosphorylation in the absence of exogenous substrates. Treatment of phosphorylated products with alkali showed a significant phosphorylation of tyrosine residues within the mRNP-proteins. An alkaline-phosphatase activity was found to be tightly associated with the mRNPs. Both heat stable and heat labile alkaline phosphatase activities were found in the mRNPs. Heat labile alkaline phosphatase is the major isoenzyme form of the mRNPs. The existence of both protein kinase(s) and alkaline phosphatase activities in placental free cytoplasmic mRNPs might suggest that a balance between phosphorylation, specifically on tyrosine residues, and dephosphorylation states of some of the mRNP-proteins is relevant for their physiological functions, and may therefore play a role in the regulation of mRNPs' metabolism and, consequently, in mRNA translation.

Adenosine Triphosphate↗
PubMed1984

Location of RNase and RNase inhibitor on free cytoplasmic mRNA-protein particles from human placenta.

Free cytoplasmic mRNPs were isolated from human placenta. An activity of RNase was associated with these particles but was mostly inhibited by a labile protein inhibitor. Both RNase and RNase inhibitor were extractable from mRNPs by 0.5 M KCl. The nature of the association of the RNase-RNase inhibitor complex with mRNPs makes it suitable as a putative system for control of expression and turnover of mRNPs and therefore of protein synthesis.

Cytoplasm↗
PubMed1984

The effect of protein and RNA synthesis inhibitors on the synthesis and secretion of hCG, alpha- and beta-hCG subunits, in organ culture.

The relationship between the rate of RNA and protein synthesis and that of and its alpha- and beta-subunits was studied in an organ culture system using RNA and protein synthesis inhibitors. It was found that inhibiting protein synthesis by puromycin or cycloheximide results also in a nearly complete inhibition of the synthesis and/or processing of RNA molecules. Protein synthesis was found to be dependent upon continuous poly A(-) RNA synthesis. The intracellular content of hCG, alpha-hCG and beta-hCG remains constant during the entire incubation period and does not change in response to any of the inhibitors used. However, in the presence of some inhibitors, changes are observed in the amount of the secreted hormone and its two subunits as well as in the association ability of the subunits to form the complete native hormone. Nevertheless, synthesis and secretion of hCG, alpha-hCG and beta-hCG were almost identically affected by alpha-amanitin. These results might suggest that the mRNAs coding for the two subunits have the same relative metabolic stability and/or that these mRNAs are mobilized molecules from free cytoplasmic mRNP pools. The specific alpha- and beta-mRNAs seem to be less stable, however, than the mRNAs coding for the other newly synthesized proteins, since the inhibition of alpha- and beta-hCG synthesis by alpha-amanitin was consistently higher than the corresponding average inhibition of total protein synthesis.

Amanitins↗
PubMed1982

RNA synthesis in cultured human placenta.

The in vitro synthesis of RNA in the human placental tissue, incubated in organ culture, was investigated. We followed the synthesis of the poly A(-) and poly A(+) RNA fractions, and investigated the distribution of the newly synthesized RNA among the subcellular fractions isolated from first and third trimester placentas. The poly A(-) RNA was the major fraction of the RNA synthesized in vitro. The incorporation of [3H]uridine into the poly A(+) RNA fraction was very low. As protein synthesis occurred during the entire incubation period, we suggest the presence of a pool of mRNA molecules in the form of mRNP particles.

DNA↗
PubMed1982

The in vitro synthesis and secretion of alkaline phosphatase from first trimester human decidua.

We studied the in vitro synthesis and secretion of alkaline phosphatase by human first trimester decidual tissue incubated in organ culture. Decidua synthesizes two different alkaline phosphatase isoenzymes; heat stable and heat labile. decidual tissue maintains a constant pool of alkaline phosphatases. The synthesis of alkaline phosphatase may be the driving force for its secretion. The de novo synthesis and secretion rate of alkaline phosphatases were also investigated. The higher specific radioactivities of the secreted enzymes than those found in the tissue may suggest that newly synthesized alkaline phosphatase is preferentially released. The intracellular distribution of the alkaline phosphatase isoenzymes was compared as well. The characteristics of the two isoenzymes are different in human decidua of maternal origin from those previously reported in the human placenta originating from embryonic stem cells.

Alkaline Phosphatase↗
PubMed1982

The synthesis and secretion of human placental lactogen (hPL) in cultured term placenta.

We studied the in vitro synthesis and secretion of hPL by human term placental tissue incubated in organ culture. Placental tissue maintains a constant pool of hPL. The synthesis of hPL may be the driving force for its secretion. The de novo synthesis and secretion rates of hPL were also investigated. The higher specific radioactivities of the secreted hPL than those found in the tissue may suggest that newly synthesized hPL is preferentially released. The intracellular distribution of hPL was also compared.

Female↗
PubMed1979

The synthesis and secretion of human chorionic gonadotropin by tissue slices from first trimester placentas.

Placental tissue slices from first trimester placentas synthesize and secrete proteins labeled by radioactive glucosamine are preferentially secreted as compared to proteins in general. One of the proteins synthesized and secreted is hCG. Processing and secretion of proteins, including hCG, by the tissue slices need a two-hour period. Both secretion and glycosylation of the protein can take place independently of protein synthesis. A method was developed for the specific determination of newly synthesized radioactive hCG in placental tissue.

Chorionic Gonadotropin↗