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PubMed2005

Patients with familial biparental hydatidiform moles have normal methylation at imprinted genes.

In molar tissues from patients with recurrent biparental hydatidiform moles, we could previously demonstrate that differentially methylated regions (DMRs) of four imprinted genes are abnormally methylated on the maternal alleles. It remained unclear if this abnormal methylation originated de novo in the molar tissues or if it is even recognizable in the patient somatic tissues. To address this question, we investigated the DNA methylation of four imprinted genes in total blood from the two sister-patients. Here, we show that both patients retain normal methylation levels at the DMRs of the four genes in blood tissues. For two maternally expressed genes, we could use informative SNPs to follow the inheritance of the abnormally methylated maternal alleles in the molar tissues. We find that the transmitted abnormally methylated maternal alleles to the moles originated from the maternal grandmother and that the same alleles are not methylated in the patients. Our data suggest that the abnormal methylation in familial biparental molar tissues was acquired de novo in the patients'germline as a result of a false reprogramming or during the postzygotic development of the conceptuses that led to moles.

Alleles↗
PubMed1983

The structure and nucleotide sequence of the 5' end of the human c-myc oncogene.

We have established the structure and nucleotide sequence of the 5' end of the human c-myc oncogene, using a cloned genomic fragment isolated from a fetal liver library (clone lambda MC41) and cloned cDNA from the human leukemic cell line K562. The human c-myc oncogene consists of three exons and two introns. Primer extension of the human c-myc mRNA of three different cell lines and S1 nuclease protection experiments served to establish the position of two transcription initiation sites. The splicing site of the first exon-intron boundary was determined by comparative analysis of the sequences of the genomic and cDNA clones. The first exon contains termination codons in all three reading frames and no translation initiation signals, confirming our previous observation that the c-myc mRNA has a long 5' noncoding sequence. This first exon also was found to be utilized in the formation of c-myc mRNAs in a variety of human cell lines.

Base Sequence↗
PubMed1998

Identification of the Meg1/Grb10 imprinted gene on mouse proximal chromosome 11, a candidate for the Silver-Russell syndrome gene.

In a systematic screen for maternally expressed imprinted genes using subtraction hybridization with androgenetic and normal fertilized mouse embryos, seven candidate maternally expressed genes (Megs) have been isolated, including the H19 and p57(Kip2) genes that are known to be maternally expressed. Herein, we demonstrate that an imprinted gene, Meg1, is apparently identical to Grb10 (growth factor receptor-bound protein 10), which is located on mouse proximal chromosome 11. Grb10 protein was reported to bind to the insulin receptor and/or the insulin-like growth factor (IGF) I receptor via its src homology 2 domain and to inhibit the associated tyrosine kinase activity that is involved in the growth promoting activities of insulin and IGFs (IGF-I and -II). Thus, it is probable that Meg1/Grb10 is responsible for the imprinted effects of prenatal growth retardation or growth promotion caused by maternal or paternal duplication of proximal chromosome 11 with reciprocal deficiencies (MatDp.prox11 or PatDp.prox11), respectively. In the human, it has been reported that the maternal uniparental disomy 7 is responsible for the Silver-Russell syndrome (SRS) whose effects include pre- and postnatal growth retardation and other dysmorphologies. The human homologue GRB10 on chromosome 7q11.2-12 is a candidate gene for Silver-Russell syndrome.

Animals↗
PubMed1999

Enhancer competition between H19 and Igf2 does not mediate their imprinting.

The linked H19 and Igf2 genes on mouse distal chromosome 7 are subject to genomic imprinting. Competition between the promoters of the genes for transcription from shared enhancers has been proposed as an explanation for the coordinate expression and reciprocal imprinting of these two genes. To test this model, we have used Cre-loxP technology to generate in mice a conditional deletion of the H19 promoter and structural gene that leaves no transcription unit in the locus. Contrary to the prediction of enhancer competition we find that transcriptional activity from the H19 promoter is not required for the imprinted silencing of the Igf2 gene.

Alleles↗
PubMed1997

Genomic deletion of an imprint maintenance element abolishes imprinting of both insulin-like growth factor II and H19.

Insulin-like growth factor II (Igf2) is maternally imprinted in normal tissues with only the paternal copy of the gene being transcribed, whereas the contiguous gene H19 is paternally imprinted. Dysregulation of IGF2 imprinting is commonly observed in Wilms' tumor and other human tumors. Previous work comparing promoter-specific imprinting of human and mouse Igf2 suggested the presence of a cis element upstream of Igf2 that regulates or maintains the imprinting of three downstream promoters. To explore the molecular mechanism of maintenance of genomic imprinting, we targeted the region between insulin 2 and Igf2, where the cis imprint maintenance element (IME) resides in mouse fibroblasts. In those clones in which the targeting vector was randomly integrated into the genome, mouse Igf2 remained imprinted. However, when the targeted region containing the IME was deleted by homologous recombination, whether from the paternal or maternal allele, activation of the imprinted maternal allele of Igf2 was observed. In addition, there was a loss of H19 imprinting when the IME was deleted. The requirement of IME from both parental alleles for the maintenance of genomic imprinting thus suggests the importance of a spatial structure of DNA around Igf2 and H19. Modifications in the IME, like abnormal methylation in Wilms' tumors, may represent a novel mechanism for loss of genomic imprinting.

Animals↗
PubMed2002

Dual promoter structure of mouse and human fatty acid translocase/CD36 genes and unique transcriptional activation by peroxisome proliferator-activated receptor alpha and gamma ligands.

Fatty acid translocase (FAT)/CD36 is a glycoprotein involved in multiple membrane functions including uptake of long-chain fatty acids and oxidized low density lipoprotein. In mice, expression of the gene is regulated by peroxisome proliferator-activated receptor (PPAR) alpha in the liver and by PPAR gamma in the adipose tissues (Motojima, K., Passilly, P. P., Peters, J. M., Gonzalez, F. J., and Latruffe, N. (1998) J. Biol. Chem. 273, 16710-16714). However, the time course of PPAR alpha ligand-induced expression of FAT/CD36 in the liver, and also in the cultured hepatoma cells, is significantly slower than those of other PPAR alpha target genes. To study the molecular mechanism of the slow transcriptional activation of the gene by a PPAR ligand, we first cloned the 5' ends of the mRNA and then the mouse gene promoter region from a genomic bacterial artificial chromosome library. Sequencing analyses showed that transcription of the gene starts at two initiation sites 16 kb apart and splicing occurs alternatively, producing at least three mRNA species with different 5'-noncoding regions. The PPAR alpha ligand-responsive promoter in the liver was identified as the new upstream promoter where we found several possible binding sites for lipid metabolism-related transcriptional factors but not for PPAR. Neither promoter responded to a PPAR alpha ligand in the in vitro or in vivo reporter assays using cultured hepatoma cells and the liver of living mice. We also have cloned the human FAT/CD36 gene from a bacterial artificial chromosome library and identified a new independent promoter that is located 13 kb upstream of the previously reported promoter. Only the upstream promoter responded to PPAR alpha and PPAR gamma ligands in a cell type-specific manner. The absence of PPRE in the responding upstream promoter region, the delayed activation by the ligand, and the results of the reporter assays all suggested that transcriptional activation of the FAT/CD36 gene by PPAR ligands is indirectly dependent on PPAR.

5' Untranslated Regions↗
PubMed1999

Methylation imprinting of H19 and SNRPN genes in human benign ovarian teratomas.

In humans, studies of female germ cells are very limited by ethics. The current study investigated the usefulness of benign ovarian teratomas as a substitute for ova in analyses of imprinted genes. Twenty-five human benign ovarian teratomas were typed with 45 microsatellite DNA markers and classified according to their genotypic features. Two oppositely imprinted genes, H19 and SNRPN, were then chosen for analysis of their methylation states in these tumors. These analyses revealed that benign ovarian teratomas consist of a mixture of genetically and epigenetically heterogeneous cell populations. In contrast to previous reports, we could document only one case rising from germ cells by meiosis-II nondisjunction. H19 and SNRPN were methylated in individual teratomas to various degrees, ranging from normal somatic cell to expected ovum levels. The allele with residual methylation of H19 was consistent with that methylated in the patient's blood DNA, thus being of paternal origin. Degrees of H19 hypomethylation and SNRPN hypermethylation increased as the cellular origin of the tumors advanced in oogenesis and were closely correlated in individual teratomas. These results could be best explained by the assumption that the primary imprinting is a progressively organized process and suggest that the establishment of primary imprints on different genes might be mechanistically linked, even when those genes are oppositely imprinted.

Autoantigens↗
PubMed2002

Association of in vitro fertilization with Beckwith-Wiedemann syndrome and epigenetic alterations of LIT1 and H19.

Recent data in humans and animals suggest that assisted reproductive technology (ART) might affect the epigenetics of early embryogenesis and might cause birth defects. We report the first evidence, to our knowledge, that ART is associated with a human overgrowth syndrome-namely, Beckwith-Wiedemann syndrome (BWS). In a prospective study, the prevalence of ART was 4.6% (3 of 65), versus the background rate of 0.8% in the United States. A total of seven children with BWS were born after ART-five of whom were conceived after intracytoplasmic sperm injection. Molecular studies of six of the children indicate that five of the six have specific epigenetic alterations associated with BWS-four at LIT1 and one at both LIT1 and H19. We discuss the implications of our finding that ART is associated with human overgrowth, similar to the large offspring syndrome reported in ruminants.

Adult↗
PubMed2001

Deletion of a nuclease-sensitive region between the Igf2 and H19 genes leads to Igf2 misregulation and increased adiposity.

The insulin-like growth factor 2 gene (Igf2) is imprinted in most somatic tissues of the mouse with the exception of the choroid plexus and leptomeninges of the brain, where it is expressed from both alleles. The imprinting of Igf2 is dependent upon an imprinting control region (ICR) that lies 90 kb 3' of the gene and acts as a chromatin insulator to block enhancers that lie further 3' on the chromosome. Based on this model we would expect that enhancers of brain-specific expression of Igf2 would lie 5' of the ICR, and thus be insensitive to its action. Here we describe a 12 kb deletion of a region 5' of the ICR that is hypersensitive to nuclease digestion in chromatin. Its deletion results in a biallelic decrease in expression of Igf2, but not H19, in the brain, consistent with the proposal that it encodes a positive regulatory element. In addition, the deletion results in a minor relaxation of Igf2 imprinting in skeletal muscle and tongue. Lastly, the reduction in IGFII expression in the adult is accompanied by increased fat deposition and occasional obesity. Overweight animals are hypophagic, suggesting that IGFII affects fat metabolism rather than feeding behavior in adult mice.

Animals↗
PubMed1996

Mouse/human sequence divergence in a region with a paternal-specific methylation imprint at the human H19 locus.

We have identified a region with characteristics of a paternal-specific methylation imprint at the human H19 locus. This region, extending from -2.0 kb upstream to the start of transcription, is heavily methylated in sperm and on the paternal allele in somatic cells. This methylation was preserved during pre-implantation. Structural analysis revealed the presence of CpG islands and a large direct repeat with a 400 bp sequence reiterated several times, but no significant sequence homology to the corresponding region of the mouse H19 gene. These findings could suggest a role for secondary DNA structure in genomic imprinting across the species, and they also present a puzzling aspect of the evolution of the H19 regulatory region in human and mouse.

Alleles↗
PubMed2000

The H19 methylation imprint is erased and re-established differentially on the parental alleles during male germ cell development.

Differences in DNA methylation distinguish the maternal and paternal alleles of many imprinted genes. Allele-specific methylation that is inherited from the gametes and maintained throughout development has been proposed as a candidate imprinting mark. To determine how methylation is established in the germline, we have analyzed the allelic methylation patterns of the maternally expressed, paternally methylated H19 gene during gametogenesis in the mouse embryo. We show here that both parental alleles are devoid of methylation in male and female mid-gestation embryonic germ cells, suggesting that methylation imprints are erased in the germ cells prior to this time. In addition, we demonstrate that the subsequent hypermethylation of the paternal and maternal alleles in the male germline occurs at different times. Although the paternal allele becomes hypermethylated during fetal stages, methylation of the maternal allele begins during perinatal stages and continues postnatally through the onset of meiosis. The differential acquisition of methylation on the parental H19 alleles during gametogenesis implies that the two unmethylated alleles can still be distinguished from each other. Thus, in the absence of DNA methylation, other epigenetic mechanism(s) appear to maintain parental identity at the H19 locus during male germ cell development.

Alleles↗
PubMed2005

IVF results in de novo DNA methylation and histone methylation at an Igf2-H19 imprinting epigenetic switch.

Recent studies suggest that IVF and assisted reproduction technologies (ART) may result in abnormal genomic imprinting, leading to an increased frequency of Angelman syndrome (AS) and Beckwith-Weidemann syndrome (BWS) in IVF children. To learn how ART might alter the epigenome, we examined morulas and blastocysts derived from C57BL/6J X M. spretus F1 mice conceived in vivo and in vitro and determined the allelic expression of four imprinted genes: Igf2, H19, Cdkn1c and Slc221L. IVF-derived mouse embryos that were cultured in human tubal fluid (HTF) (Quinn's advantage) media displayed a high frequency of aberrant H19 imprinting, whereas in vivo and IVF embryos showed normal maternal expression of Cdkn1c and normal biallelic expression of Igf2 and Slc221L. Embryonic stem (ES) cells derived from IVF blastocysts also showed abnormal Igf2/H19 imprinting. Allele-specific bisulphite PCR reveals abnormal DNA methylation at a CCCTC-binding factor (CTCF) site in the imprinting control region (ICR), as the normally unmethylated maternal allele acquired a paternal methylation pattern. Chromatin immunoprecipitation (ChIP) assays indicate an increase of lysine 4 methylation (dimethyl Lys4-H3) on the paternal chromatin and a gain in lysine 9 methylation (trimethyl Lys9-H3) on the maternal chromatin at the same CTCF-binding site. Our results indicate that de novo DNA methylation on the maternal allele and allele-specific acquisition of histone methylation lead to aberrant Igf2/H19 imprinting in IVF-derived ES cells. We suggest that ART, which includes IVF and various culture media, might cause imprinting errors that involve both aberrant DNA methylation and histone methylation at an epigenetic switch of the Igf2-H19 gene region.

Animals↗
PubMed1992

Nuclear-encoded chloroplast ribosomal protein L12 of Nicotiana tabacum: characterization of mature protein and isolation and sequence analysis of cDNA clones encoding its cytoplasmic precursor.

Poly(A)+ mRNA isolated from Nicotiana tabacum (cv. Petite Havana) leaves was used to prepare a cDNA library in the expression vector lambda gt11. Recombinant phage containing cDNAs coding for chloroplast ribosomal protein L12 were identified and sequenced. Mature tobacco L12 protein has 44% amino acid identity with ribosomal protein L7/L12 of Escherichia coli. The longest L12 cDNA (733 nucleotides) codes for a 13,823 molecular weight polypeptide with a transit peptide of 53 amino acids and a mature protein of 133 amino acids. The transit peptide and mature protein share 43% and 79% amino acid identity, respectively, with corresponding regions of spinach chloroplast ribosomal protein L12. The predicted amino terminus of the mature protein was confirmed by partial sequence analysis of HPLC-purified tobacco chloroplast ribosomal protein L12. A single L12 mRNA of about 0.8 kb was detected by hybridization of L12 cDNA to poly(A)+ and total leaf RNA. Hybridization patterns of restriction fragments of tobacco genomic DNA probed with the L12 cDNA suggested the existence of more than one gene for ribosomal protein L12. Characterization of a second cDNA with an identical L12 coding sequence but a different 3'-noncoding sequence provided evidence that at least two L12 genes are expressed in tobacco.

Amino Acid Sequence↗
PubMed2001

Culture of preimplantation mouse embryos affects fetal development and the expression of imprinted genes.

Culture of preimplantation mammalian embryos and cells can influence their subsequent growth and differentiation. Previously, we reported that culture of mouse embryonic stem cells is associated with deregulation of genomic imprinting and affects the potential for these cells to develop into normal fetuses. The purpose of our current study was to determine whether culture of preimplantation mouse embryos in a chemically defined medium (M16) with or without fetal calf serum (FCS) can affect their subsequent development and imprinted gene expression. Only one third of the blastocysts that had been cultured from two-cell embryos in M16 medium complemented with FCS developed into viable Day 14 fetuses after transfer into recipients. These M16 + FCS fetuses were reduced in weight as compared with controls and M16 fetuses and had decreased expression of the imprinted H19 and insulin-like growth factor 2 genes associated with a gain of DNA methylation at an imprinting control region upstream of H19. They also displayed increased expression of the imprinted gene Grb10. The growth factor receptor binding gene Grb7, in contrast, was strongly reduced in its expression in most of the M16 + FCS fetuses. No alterations were detected for the imprinted gene MEST: Preimplantation culture in the presence of serum can influence the regulation of multiple growth-related imprinted genes, thus leading to aberrant fetal growth and development.

Animals↗
PubMed1998

Studying early nodulin gene ENOD40 expression and induction by nodulation factor and cytokinin in transgenic alfalfa.

ENOD40, an early nodulin gene, is expressed following inoculation with Rhizobium meliloti or by adding R. meliloti-produced nodulation (Nod) factors or the plant hormone cytokinin to uninoculated roots. We isolated two MsENOD40 clones, designated MsENOD40-1 and MsENOD40-2, with distinct promoters from an alfalfa (Medicago sativa cv Chief) genomic library. The promoters were fused to the reporter gene uidA (gus), and the constructs were introduced into alfalfa. We observed that the MsENOD40-1 construct was expressed almost exclusively under symbiotic conditions. The MsENOD40-2 construct was transcribed under both symbiotic and nonsymbiotic conditions and in nonnodular and nodular tissues. Both MsENOD40 promoter-gus constructs were similarly expressed as nodules developed, and both were expressed in roots treated with 6-benzylaminopurine or purified Nod factor. However, no blue color was detected in nodule-like structures induced by the auxin transport inhibitor N-1-(naphthyl)phthalamic acid on roots of plants containing the MsENOD40-1 promoter construct, whereas pseudonodules from plants containing the MsENOD40-2 promoter construct stained blue. A 616-bp region at the distal 5' end of the promoter is important for proper spatial expression of MsENOD40 in nodules and also for Nod-factor and cytokinin-induced expression.

Bacterial Proteins↗
PubMed1997

A 5' 2-kilobase-pair region of the imprinted mouse H19 gene exhibits exclusive paternal methylation throughout development.

The imprinted mouse H19 gene is hypermethylated on the inactive paternal allele in somatic tissues and sperm. Previous observations from a limited analysis have suggested that methylation of a few CpG dinucleotides in the region upstream from the start of transcription may be the mark that confers parental identity to the H19 alleles. Here we exploit bisulfite mutagenesis coupled with genomic sequencing to derive the methylation status of 68 CpGs that reside in a 4-kb region 5' to the start of transcription. This method reveals a 2-kb region positioned between 2 and 4 kb upstream from the start of transcription that is strikingly differentially methylated in midgestation embryos. At least 12 of the cytosine residues in this region are exclusively methylated on the paternal allele in blastocysts. In contrast, a 350-bp promoter-proximal region is less differentially methylated in midgestation embryos and, like most of the genome, is largely devoid of methylation on both alleles in blastocysts. We also demonstrate exclusive expression of the maternal H19 allele in the embryos that exhibit paternal methylation of the upstream 2-kb region. These data suggest that the 2-kb differentially methylated region acts as a key regulatory domain for imprinted H19 expression.

Alleles↗
PubMed1997

Ribonucleic acid expression of the clustered imprinted genes, p57KIP2, insulin-like growth factor II, and H19, in adrenal tumors and cultured adrenal cells.

The recently cloned cyclin-dependent kinase inhibitor gene p57KIP2 is genomically imprinted and located on human chromosome 11p15.5. This region contains two other imprinted genes, insulin-like growth factor II (IGF-II) and H19, both of which seem to be implicated in adrenal neoplasms. We analyzed the expression of the putative tumor suppressor p57KIP2 gene by Northern blotting in normal and hyperplastic adrenals, adrenocortical tumors, and pheochromocytomas. The expression of p57KIP2 messenger ribonucleic acid (mRNA) correlated positively with H19 and negatively with IGF-II RNA in adrenocortical tissues. p57KIP2 mRNA (and H19 RNA) was abundantly expressed in normal human adrenals, adrenocortical adenomas from patients with Cushing's or Conn's syndrome or without clinical evidence of hormone overproduction, hyperplastic adrenals, and tumor-adjacent adrenal tissues, in which IGF-II mRNA expression was low. In most adrenocortical carcinomas and virilizing adrenal adenomas, very low levels of both p57KIP2 and H19 RNAs were observed, whereas IGF-II was highly expressed. In pheochromocytomas, p57KIP2 and H19 RNA expression was highly variable, but on the average it was about 45% and 27%, respectively, of that in normal and tumor-adjacent adrenals. In cultured adrenocortical cells, ACTH and dibutyryl cAMP treatment slightly reduced the predominant 1.7-kilobase (kb) transcript of p57KIP2 gene, but induced a 2.5-kb transcript with a simultaneous increase in H19 RNA expression. The stimulatory effect of ACTH on the 2.5-kb p57KIP2 and H19 transcript accumulation was enhanced by exogenous IGF-II and IGF-I. Our data show that p57KIP2 and H19 RNAs are expressed usually in parallel in normal and pathological adrenocortical tissues. The decreased expression of both p57KIP2 and H19 RNAs in conjunction with elevated IGF-II mRNA expression in hormonally active adrenocortical carcinomas suggests that the loss of expression of the putative tumor suppressor genes p57KIP2 and H19 may be involved in the pathogenesis of these neoplasms.

Adrenal Gland Neoplasms↗