Impressions of imprints.
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Angelman Syndrome↗
Biomedical subjects
R Ohlsson
Publications and source records attributed to R Ohlsson.
The non-viability of uniparental mouse conceptuses correlates with the loss of the products of imprinted genes.
Diploid parthenogenetic or androgenetic mouse conceptuses produce characteristic and opposite mutant phenotypes and are non-viable, presumably due to different contributions from the maternal and paternal genomes. This is likely to be the result of the preferential expression of only one parent's copy of certain genes in the offspring. So far, four such endogenous imprinted genes are known: the paternal alleles of Igf2 and Snrpn and the maternal alleles of Igf2r and H19 are active, while their opposite parental alleles are inactive. Here we demonstrate that the expression patterns of the Igf2 and Igf2r genes in androgenetic and parthenogenetic conceptuses correlate with which parental alleles normally express them, implying that the imprint can be maintained in the absence of the other parent's genome for these genes. This also indicates that both types of uniparental conceptuses are lacking developmentally important gene products. We did find, however, that the H19 gene was highly expressed not only in the parthenogenetic conceptus, but also in giant trophoblasts and secondary giant cells in the androgenetic placenta, in spite of the imprinting of the H19 gene in normal mouse extra embryonic tissues. We discuss these observations with respect to the non-viability of uniparental conceptuses and the reciprocal imprinting patterns of the Igf2 and H19 genes.
Animals↗
Overlapping patterns of IGF2 and H19 expression during human development: biallelic IGF2 expression correlates with a lack of H19 expression.
The spatial patterns of IGF2 and H19 gene expression are strikingly similar during parts of human embryonic/fetal and early postnatal development. Notable exceptions were found with the ciliary anlage of the embryonic retina and the choroid plexus/leptomeninges, where transcripts from the IGF2 but not the H19 locus could be detected. Moreover, in contrast to the other tissue samples examined, the choroid plexus/leptomeninges expressed both parental IGF2 alleles. Whilst RNase protection analysis revealed a weak activity of the P1 promoter in the choroid plexus/leptomeninges, the P2, P3 and P4 promoters were all active wherever IGF2 was expressed. We discuss these observations with respect to a hypothesized coordinated control of the reciprocally imprinted and closely linked IGF2 and H19 loci.
Alleles↗
The cell type-specific IGF2 expression during early human development correlates to the pattern of overgrowth and neoplasia in the Beckwith-Wiedemann syndrome.
Overstimulation by insulin-like growth factor II is implied in several overgrowth conditions and childhood cancers. We have therefore studied spatial and temporal expression patterns of the insulin-like growth factor II gene (IGF2) and the insulin-like growth factor type 1 receptor gene during normal human development (5.5 to 23.0 weeks postfertilization). The set of cell types with the most abundant IGF2 expression correlated strikingly to the organomegaly and tumor predisposition of the Beckwith-Wiedemann syndrome. Intrauterine growth and postnatal organ weights of a prematurely born child with a full-blown syndrome are presented. The cell type-specific IGF2 expression of these organs and of multifocal Wilms' tumors from two other children affected by the Beckwith-Wiedemann syndrome were also studied. The results clarify and extend previous findings concerning human prenatal IGF2 expression and are consistent with a short range overstimulatory role of locally produced IGF II ensuing after the first trimester in the Beckwith-Wiedemann syndrome.
Beckwith-Wiedemann Syndrome↗
Successive activation of the platelet-derived growth factor beta receptor and platelet-derived growth factor B genes correlates with the genesis of human choriocarcinoma.
The hydatidiform mole is a benign disease of the placenta characterized by the absence of the maternal genome. Approximately 3% of the reported cases will develop into malignant choriocarcinoma. In situ hybridization analysis reveals that the paternal platelet-derived growth factor (PDGF) beta receptor gene is up to 2 orders of magnitude more active in cytotrophoblasts of the complete hydatidiform moles than in normal placentae. The transition between hyperplasia (complete hydatidiform mole) and neoplasia (choriocarcinoma) in these cells correlates with at least a 10- to 20-fold activation of the PDGF-B gene. Since the neoplastic cytotrophoblasts have maintained an abnormally high level of PDGF beta receptor expression, we propose that a deregulated PDGF autostimulatory loop is involved in the genesis of human choriocarcinoma from hydatidiform moles.
Choriocarcinoma↗
IGF2 is parentally imprinted during human embryogenesis and in the Beckwith-Wiedemann syndrome.
The phenomenon of parental imprinting involves the preferential expression of one parental allele of a subset of chromosomal genes and has so far only been documented in the mouse. We show here, by exploiting sequence polymorphisms in exon nine of the human insulin-like growth factor 2 (IGF2) gene, that only the paternally-inherited allele is active in embryonic and extra-embryonic cells from first trimester pregnancies. In addition, only the paternal allele is expressed in tissues from a patient who suffered from Beckwith-Wiedemann syndrome. Thus the parental imprinting of IGF2 appears to be evolutionarily conserved from mouse to man and has implications for the generation of the Beckwith-Wiedemann syndrome.
Alleles↗
[Equality, needs, freedom of choice and efficiency should be considered when priorities are made in an equitable health care].
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Ethics, Medical↗
Spatial distribution of active genes implicated in the regulation of insulin-like growth factor stimulatory loops in human decidual and placental tissue of first-trimester pregnancy.
We have previously shown that the insulin-like growth factor-2 (IGF-2) gene is partially coexpressed with the IGF-1 and -2 receptor genes in proliferative cytotrophoblasts of the human extraembryonic tissue. Here we show that high levels of IGF-2 gene expression are not restricted to the embryonic tissue but can also be found in the decidua compacta. The IGF-2 gene is thus expressed at high levels in the mesenchymal stroma of the decidua to establish potentially short-range communication with primarily IGF-1 receptor-positive mesenchymal stroma cells. Conversely, the glandular and surface epithelia coexpress the IGF-1 receptor and IGF-1 genes, while the IGF-2 gene is not detected above background levels. The potential control mechanisms of these cell-cell signalling pathways were investigated by the analysis of the spatial distribution of active IGF binding proteins (IGFBP) genes. The IGFBP-3 gene is coexpressed with the IGF-2 gene in proliferative cytotrophoblasts of the embryonic placenta. While active IGFBP-1 and -2 genes in our hands cannot be detected in the embryonic placenta, all three IGFBP genes are expressed in complex and overlapping patterns in the decidua compacta. The results are discussed in terms of how the various IGFBP genes may operate in different cell types to restrict IGF local stimulatory pathways.
Blotting, Northern↗
The expression of PDGF alpha- and beta-receptors in subpopulations of PDGF-producing cells implicates autocrine stimulatory loops in the control of proliferation in cytotrophoblasts that have invaded the maternal endometrium.
In order to explain the high proliferative potential of human placental cytotrophoblasts, we have addressed the potential involvement of platelet-derived growth factor (PDGF) ligand and receptors. Although PDGF is usually described as a mitogen for cells of mesenchymal origin, we show in this report that extra-villous term placental cytotrophoblasts express the PDGF alpha- and beta-receptor genes, both in vivo and in vitro. In addition, cytotrophoblasts produce significant amounts of PDGF-B protein. By immunohistochemical analysis of receptor expression, we found that the PDGF alpha-receptors could be detected at the cell surface, while the PDGF beta-receptors were only detected intracellularly. In addition, double immunostaining analysis showed that the PDGF alpha- and beta-receptor molecules are expressed in different subpopulations of cytotrophoblasts. The addition of PDGF-AA and PDGF-BB homodimers to cytotrophoblast primary cultures induced a significant increase in DNA synthesis. We conclude, therefore, that PDGF is a growth factor for placental cytotrophoblasts and suggest that the growth of cytotrophoblasts can partly be explained by a PDGF autostimulatory loop, limited by the number of receptor-positive cytotrophoblasts.
Cell Membrane↗
[Hereditary memory: genomic imprinting and its importance for embryonal development and carcinogenesis].
When the mammalian oocyte is fertilized, a unit is formed which requires the collaboration of the parental cell genomes. In this collaboration, however, a fraction of the autosomal parental genes are provided with different values by a memory from the germ cell maturation process. In the article the importance of genomic imprinting by the parental cell genomes is discussed in terms of the regulation of embryonic development and with regard to tumourigenesis.
Cell Differentiation↗
Order of probe and nuclear protein extract addition can determine specificity of protein--DNA complexes in tested mobility shift assays.
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DNA↗
Expression of the human PDGF-B gene is regulated by both positively and negatively acting cell type-specific regulatory elements located in the first intron.
Potential cis-acting regulatory elements of the human platelet derived growth factor-B (PDGF-B) gene were identified by DNase I hypersensitive site mapping. The transcription unit was examined for the presence of hypersensitive sites in chromatin DNA isolated from human term placental cytotrophoblasts, human placental fibroblasts, the JEG-3 choriocarcinoma cell line and the U2-OS osteosarcoma cell line. A number of cell type-specific hypersensitive sites were identified, all within the 1st intron. Transient transfection of JEG-3 cells with CAT constructs containing regions of the c-sis 1st intron linked to the basal c-sis promoter identified a cell type-specific positive regulatory activity within the intron, composed of at least two distinct elements. One element appeared to be specific for JEG-3 cells, while the other was also active in U2-OS cells. The overall positive regulatory activity of the 1st intron region was specific for JEG-3 cells, but did not function as a classically defined enhancer, as it was orientation-dependent (unless stably integrated into chromatin DNA). In addition, the activator appears to require interaction with the c-sis promoter, as little or no activation was seen when either the SV40 or human beta-globin promoters were substituted for the c-sis promoter. The 1st intron also contained a negative regulatory element, which was specific for U2-OS cells and silenced an abnormally high basal c-sis promoter activity in these cells. The complexity of the transcriptional control of the PDGF-B gene is discussed.
Base Sequence↗
Angiogenesis during human extraembryonic development involves the spatiotemporal control of PDGF ligand and receptor gene expression.
We have examined the role of platelet-derived growth factor (PDGF) ligand and receptor genes in the angiogenic process of the developing human placenta. In situ hybridization analysis of first trimester placentae showed that most microcapillary endothelial cells coexpress the PDGF-B and PDGF beta-receptor genes. This observation indicates that PDGF-B may participate in placental angiogenesis by forming autostimulatory loops in capillary endothelial cells to promote cell proliferation. Endothelial cells of macro blood vessels maintained high PDGF-B expression, whereas PDGF beta-receptor mRNA was not detectable. In contrast, PDGF beta-receptor mRNA was readily detectable in fibroblast-like cells and smooth muscle cells in the surrounding intima of intermediate and macro blood vessels. Taken together, these data suggest that the PDGF-B signalling pathway appears to switch from an autocrine to a paracrine mechanism to stimulate growth of surrounding PDGF beta-receptor-positive mesenchymal stromal cells. Smooth muscle cells of the blood vessel intima also expressed the PDGF-A gene, the protein product of which is presumably targeted to the fibroblast-like cells of the mesenchymal stroma as these cells were the only ones expressing the PDGF alpha-receptor. PDGF-A expression was also detected in columnar cytotrophoblasts where it may have a potential role in stimulating mesenchymal cell growth at the base of the growing placental villi. We discuss the possibility that the regulation of the PDGF-B and beta-receptor gene expression might represent the potential targets for primary angiogenic factors.
Blotting, Northern↗
Levels of myc protein, as analyzed by flow cytometry, correlate with cell growth potential in malignant B-cell lymphomas.
We have analyzed c-myc protein expression during the cell cycle in malignant B-cell lymphomas by dual flow cytometric detection of a fluoresceinated polyclonal anti-myc antibody and propidium iodide which binds stochiometrically to DNA. The data obtained were correlated to other parameters of cell activation such as histopathological grading, expression of the activation antigen 4F2, light scatter (proportional to cellular volume), DNA synthesis and percentage of S-phase cells. The c-myc protein level was strongly correlated to parameters of DNA synthesis/content. In addition, the oncoprotein level was largely unvarying from the late G1 phase through the rest of the cell cycle in both malignant cells and normal purified B cells stimulated to proliferate in vitro.
B-Lymphocytes↗
Insulin-like growth factor 2 and short-range stimulatory loops in control of human placental growth.
Substructures of the first-trimester human placenta (within 3 months post-conception) display 'pseudo-malignant' properties. We show here, by in situ hybridization, that the insulin-like growth factor 2 (IGF-2) gene expression is particularly active in the cytotrophoblasts, which dominate these structures. Because the majority of placental IGF-2 mRNA is polysomal in extracts of first-trimester placenta, the spatial pattern of IGF-2 transcripts generally also defines the pattern of IGF-2 production. In primary trophoblast cultures, rendered quiescent by serum starvation. IGF-2 performs as a human embryonic growth factor by activating cell cycle entry/progression. Although both type 1 and 2 IGF receptor mRNAs can be found co-distributed with IGF-2 mRNA during placental development (supporting an autocrine role for IGF-2), these occasional patterns are confined to cytotrophoblasts with low proliferative potential. The reciprocity in ligand and receptor expression patterns are discussed in terms of rate-limiting steps in the involvement of IGF-2 in the proliferative phenotype of the early human placenta.
Cell Division↗
Growth factors, protooncogenes and human placental development.
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Female↗
Blastocyst implantation precedes induction of insulin-like growth factor II gene expression in human trophoblasts.
The cytotrophoblast cell population of the human embryonic conceptus proliferates rapidly during the first month following blastocyst implantation. Since the trophectoderm lineage is established in preimplantation morula/blastocysts, the scenario underlying initiation and maintenance of the rapid proliferative phenotype of cytotrophoblasts is a central issue. The insulin-like growth factor II (IGF-II) gene is highly expressed in proliferative cytotrophoblasts of first trimester placenta and performs as a placenta growth factor. To establish a temporal correlation between IGF-II expression and initiation of highly proliferative trophoblasts in human development, we employed in situ hybridization analysis of the expression of the IGF-II and human chorionic gonadotropin beta-subunit (beta-HCG) genes in human pre- and postimplantation development. The data show that the appearance of high steady-state levels of IGF-II transcripts in trophoblasts is a postimplantation event, whereas beta-HCG transcripts can already be detected in preimplantation development. This observation makes a role for endogenously produced IGF-II in the normal development of preimplantation embryos unlikely, but suggests that endogenously produced IGF-II participates in the formation and subsequent expansion of the rapid proliferative phenotype of the trophoblastic shell, following implantation.
Blastocyst↗
Transcription of protooncogenes during stimulation of normal human B lymphocytes.
Protooncogenes play important roles in the regulation of growth and differentiation of normal cells. In this study we have examined the cell cycle-dependent regulation of transcription of various protooncogenes after stimulation of human peripheral blood B lymphocytes. The transcriptional rate of various genes was determined by means of a nuclear run-on assay. We found that several protooncogenes were transcriptionally activated after stimulation (myc, p53, K-ras, H-ras, sis and ets), but with different kinetics of induction. In contrast, some oncogenes, especially those encoding membrane-associated or cytoplasmatic proteins like abl, rel or mil/raf, were transcribed at a relatively constant rate during the cell cycle.
B-Lymphocytes↗