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T H Vu

Publications and source records attributed to T H Vu.

At least 55 records · Page 3Linked to original sources
PubMed1998

Tissue-specific imprinting of the mouse insulin-like growth factor II receptor gene correlates with differential allele-specific DNA methylation.

Imprinted genes may be expressed uniparentally in a tissue- and development-specific manner. The insulin-like growth factor II receptor gene (Igf2r), one of the first imprinted genes to be identified, is an attractive candidate for studying the molecular mechanism of genomic imprinting because it is transcribed monoallelically in the mouse but biallelically in humans. To identify the factors that control genomic imprinting, we examined allelic expression of Igf2r at different ages in interspecific mice. We found that Igf2r is not always monoallelically expressed. Paternal imprinting of Igf2r is maintained in peripheral tissues, including liver, kidney, heart, spleen, intestine, bladder, skin, bone, and skeletal muscle. However, in central nervous system (CNS), Igf2r is expressed from both parental alleles. Southern analysis of the Igf2r promoter (region 1) revealed that, outside of the CNS where Igf2r is monoallelically expressed, the suppressed paternal allele is fully methylated while the expressed maternal allele is completely unmethylated. In CNS, however, both parental alleles are unmethylated in region 1. The importance of DNA methylation in the maintenance of the genomic imprint was also confirmed by the finding that Igf2r imprinting was relaxed by 5-azacytidine treatment. The correlation between genomic imprinting and allelic Igf2r methylation in CNS and other tissues thus suggests that the epigenetic modification in the promoter region may function as one of the major factors in maintaining the monoallelic expression of Igf2r.

Alleles↗
PubMed1998

Clinical manifestations of mitochondrial DNA depletion.

OBJECTIVE: We studied five new patients with mitochondrial DNA (mtDNA) depletion to better define the clinical spectrum of this disorder. BACKGROUND: mtDNA depletion has been associated with myopathy or hepatopathy, or both, in infants and young children. Involvement of the CNS and peripheral nervous system has not been clearly established. METHODS: We reviewed the clinical course and performed morphologic, biochemical, and genetic analyses of muscle samples from five patients. RESULTS: Age at onset ranged from 3 months to 5 years, and one patient survived until age 10 1/2 years. Two patients had laboratory and clinical features reminiscent of dystrophinopathy, two had evidence of brain involvement, and two had peripheral neuropathy. Muscle biopsy specimens in all patients showed abundant ragged-red fibers. Biochemistry showed cytochrome c oxidase deficiency in all patients tested and decreased activities of other respiratory chain complexes in some. CONCLUSIONS: Inheritance appeared to be autosomal recessive, suggesting that mutations in nuclear DNA are responsible for mtDNA depletion. mtDNA depletion should be considered in children with mitochondrial disorders of uncertain etiology, and criteria for diagnosis are proposed.

Blotting, Southern↗
PubMed1998

Mitochondrial DNA depletion in a patient with long survival.

We studied a 29-year-old woman with myopathy since childhood with evidence of mitochondrial DNA (mtDNA) depletion. Muscle biopsy sample showed cytochrome c oxidase (COX)-negative fibers. Biochemistry showed COX deficiency. Southern blot analysis showed 76% depletion of mtDNA as compared with controls. This patient's clinical course suggests that long survival is possible in some patients with mtDNA depletion.

Adult↗
PubMed1997

Repression of hepatitis B virus (HBV) transgene and HBV-induced liver injury by low protein diet.

Persistent infection with hepatitis B virus (HBV) is one of the primary risk factors for human hepatocellular carcinoma (HCC). In a human ecological study, we have shown that, in addition to HBV, animal food consumption also significantly contributes to the variance of HCC. To test the interacting effect of HBV and animal food consumption on the development of HCC, we investigated HBV expression in HBV transgenic mice fed three levels of casein diet. HBV expression in transgenic animals was substantially inhibited when dietary casein was reduced from the traditional level of 22% to the level of 6%. Northern analysis revealed that suppression of HBV was derived from both the upstream albumin promoter and the internal HBV promoter. Immunochemical staining of liver sections indicated that only a few hepatocytes around the central vein expressed viral surface antigen (HBsAg) in the 6% casein animals, whereas virtually all hepatocytes stained positively for HBsAg in the 22% dietary casein animals. Serum HBsAg concentrations at 4 months were increased by 1.6-, 2.1-, and 5.1- fold over baseline for animals fed the 6%, 14%, and 22% casein diets, respectively. Correspondingly, liver injury was much less severe in animals fed 6% casein diet than in those fed 14% and 22% casein diets. These results demonstrate that a low casein diet is a potent suppresser of HBV transgene and HBV-induced liver injury, suggesting that diet management may be a practical means to aid in the control HBV infection.

Animals↗
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↗
PubMed1997

Mapping of the mutations present in the genome of the Rift Valley fever virus attenuated MP12 strain and their putative role in attenuation.

The MP12 attenuated strain of Rift Valley fever virus was obtained by 12 serial passages of a virulent isolate ZH548 in the presence of 5-fluorouracil (Caplen et al., 1985. Mutagen-directed attenuation of Rift Valley fever virus as a method for vaccine development. J. Gen. Virol., 66, 2271-2277). The comparison of the M segment of the two strains has already been reported by Takehara et al. (Takehara et al., 1989. Identification of mutations in the M RNA of a candidate vaccine strain of Rift Valley fever virus. Virology 169, 452-457). We have completed the comparison and found that altogether a total of nine, 12 and four nucleotides were changed in the L, M and S segments of the two strains, respectively. Three mutations induced amino acid changes in the L protein but none of them was located in the recognized motifs conserved among RNA dependent polymerases. In the S segment, a single change modified an amino acid in the NSs protein and in the M segment, seven of the mutations resulted in amino acid changes in each of the four encoded G1, G2, 14 kDa and 78 kDa proteins. Characterization of the MP12 virus indicated that determinants for attenuation were present in each segment and that they were introduced progressively during the 12 passages in the presence of the mutagen (Saluzzo and Smith, 1990. Use of reassortant viruses to map attenuating and temperature-sensitive mutations of the Rift Valley fever virus MP-12 vaccine. Vaccine 8, 369-375). Passages 4 and 7-9 were found to be essential for introduction of temperature-sensitive lesions and attenuation. In an attempt to correlate some of the mutations with the attenuated or temperature-sensitive phenotypes, we determined by sequencing the passage level at which the different mutations appeared. This work should help to address the question of the role of the viral gene products in Rift Valley fever pathogenesis.

Animals↗
PubMed1997

Modulation of Igf2 genomic imprinting in mice induced by 5-azacytidine, an inhibitor of DNA methylation.

The adjacent genes, insulin-like growth factor 2 (Igf2) and H19, are imprinted in both mouse and human. While Igf2 is expressed from the paternal allele, H19 is transcribed exclusively from the maternal allele. To explore the underlying mechanism of Igf2 and H19 imprinting, we studied the effect of DNA demethylation on allelic expression by injecting mice with the demethylating agent 5-azacytidine (5-aza-C). We observed a > or = 2-fold increase in the abundance of Igf2 mRNA in liver from treated mice compared with that of control mice. There was no significant change in Igf2 or H19 expression in brain. In the 5-aza-C-treated mice, there was dramatic modulation of Igf2 imprinting. In some tissues, Igf2 was expressed biallelically, while in other tissues, the paternal allele was silenced and the normally imprinted maternal allele was expressed, an example of allelic switching. There was no change in the normal biallelic pattern of Igf2 expression in brain. H19, on the other hand, remained imprinted in all tissues in mice treated with 5-aza-C. These results provide the first example of a pharmacological manipulation of genomic imprinting of an endogenous gene in vivo and further implicate DNA methylation as an important factor in maintaining the differential allelic expression of the Igf2 gene.

Animals↗
PubMed1996

Increased expression of the insulin-like growth factor-II gene in Wilms' tumor is not dependent on loss of genomic imprinting or loss of heterozygosity.

Loss of imprinting of insulin-like growth factor-II gene (IGF2) and/or loss of heterozygosity at the 11p15 loci have been postulated to be responsible for IGF2 overexpression in Wilms' tumor. In order to delineate the mechanism of IGF2 overexpression in Wilms' tumors, we have genotyped the 11p15-11p13 chromosomal region and determined allelic expression of IGF2 and H19 in both tumor tissue and in normal adjacent kidney tissue from 40 patients with Wilms' tumor. In five of the eight subjects informative for the ApaI IGF2 polymorphism, loss of imprinting of IGF2 was observed in both normal and tumor tissues. A significant increase (>5-fold) in IGF2 expression in tumor tissues compared to the normal adjacent kidney tissue was observed regardless of the IGF2 imprinting or the chromosome 11p15 heterozygosity status. In each case, the overexpression of IGF2 in the tumors was accompanied by activation of all four IGF2 promoters. Our data indicate that alterations of IGF2 imprinting occurred in normal adjacent kidney tissue before tumorigenesis and that the IGF2 overexpression in Wilms' tumor tissue occurs through a loss of heterozygosity- or loss of imprinting-independent process.

Alleles↗
PubMed1996

Promoter-specific modulation of insulin-like growth factor II genomic imprinting by inhibitors of DNA methylation.

The insulin-like growth factor II (IGF-II) gene is maternally imprinted in most normal tissues with only the paternal allele being transcribed. In several human tumors, however, IGF-II is expressed from both parental alleles. To explore the underlying mechanism of IGF-II imprinting, we have examined the effect of DNA demethylation in cultured human and mouse astrocyte cells. An increased expression of IGF-II was observed when these cells were treated with the DNA demethylating agents, 5-azacytidine or 2-deoxy-5-azacytidine. Allelic analysis indicated that, following DNA demethylation, the increment in IGF-II mRNA was primarily derived from the normally suppressed maternal allele. Examination of promoter usage revealed that only the most proximal promoter (mP3 in mouse and hP4 in human) responded to DNA demethylating agents, whereas the expression of IGF-II from the other promoters remained unchanged. The enhanced expression of IGF-II from these promoters suggests the presence of a methylation-response element in or near mP3 and hP4. This study indicates that DNA demethylating agents increase IGF-II expression primarily by stimulating the normally imprinted allele through the activation of the most proximal IGF-II promoter.

Animals↗
PubMed1996

Alterations in the promoter-specific imprinting of the insulin-like growth factor-II gene in Wilms' tumor.

The human IGF2 gene, which encodes a mitogenic peptide required for normal fetal development, is overexpressed in many types of tumors. IGF2 is transcribed from four promoters (P1-P4), and in most tissues, the gene is imprinted. In this study, we have analyzed IGF2 promoter usage and determined the allelic expression from each promoter in 19 ApaI- and 22 AluI-heterozygous Wilms' tumors. Loss of IGF2 imprinting (LOI) was observed in 8 ApaI-informative tumors. In these tumors, each parental allele was expressed in equal abundance, indicating that there was complete relaxation of IGF2 imprinting. In each LOI tumor, expression from promoter P1 as well as from the normally imprinted promoters P2-P4 was biallelic. In the 11 ApaI-informative tumors which maintained IGF2 imprinting (maintenance of imprinting), transcription from promoters P2-P4 was always monoallelic, while transcripts from P1 were derived from either one or both alleles. The lack of consistency of IGF2 imprinting of promoter P1 in maintenance of imprinting tumors was also observed in normal fetal tissues of 6 12 weeks gestation, suggesting a similarity in IGF2 regulation between Wilms' tumors and embryonic tissue development. These data suggest that the increased expression of IGF2 in Wilms' tumor may be caused either by biallelic gene expression in LOI tumors from promoters P2-P4 and/or by a reversion to an earlier stage of development which is characterized by increased synthesis of this fetal growth factor.

Alleles↗
PubMed1996

Multiple mitochondrial DNA deletions in sporadic inclusion body myositis: a study of 56 patients.

Inclusion body myositis, a chronic inflammatory disorder, is the most common cause of myopathy in adults over the age of 50. Diagnosis is based on clinical features and distinctive morphological findings by both light and electron microscopy. The causes of inclusion body myositis are still unknown. Ultrastructural mitochondrial changes and ragged-red fibers are common in patients with sporadic inclusion body myositis, and multiple [correction of mutiple] mitochondrial DNA (mtDNA) deletions have been reported in 3 such patients, suggesting that mtDNA mutations may have a pathogenetic role. We studied 56 patients with sporadic inclusion body myositis, using a combination of clinical, morphological, biochemical, and molecular genetic analyses to determine the frequency and the distribution of mtDNA deletions. Using the polymerase chain reaction, we found multiple mtDNA deletions in 73% of patients, compared to 40% of normal age-matched control subjects and 47% of disease control subjects. The presence of deletions correlated with morphological evidence of ragged-red, cytochrome c oxidase-negative fibers, and with defects of complexes I and IV of the electron transport chain. Although aging may account for a proportion of mtDNA deletions in patients with sporadic inclusion body myositis and control subjects, mtDNA alterations may be accelerated in sporadic inclusion body myositis.

Adult↗
PubMed1996

Mitochondrial myopathy simulating spinal muscular atrophy.

A patient with a severe progressive neuromuscular disorder resembling spinal muscular atrophy is reported. The initial muscle biopsy was consistent with a denervating process. DNA analysis did not reveal deletions in exons 7 and 8 of the survival motor neuron gene. Histology, histochemistry, and biochemistry of a second muscle biopsy suggested mitochondrial myopathy accompanying the denervating features. Immunohistochemistry using anti-DNA antibodies revealed only nuclear staining in skeletal muscle, suggesting mitochondrial DNA depletion. In patients with clinical features of spinal muscular atrophy and no deletions in the survival motor neuron gene, mitochondrial DNA depletion should be considered.

Biopsy↗
PubMed1996

Lack of effect of recombinant human growth hormone (GH) on muscle morphology and GH-insulin-like growth factor expression in resistance-trained elderly men.

Vastus lateralis muscle samples were obtained by needle biopsy from 18 healthy elderly men (65-82 yr) participating in a double blind, placebo (PL)-controlled trial of recombinant human GH (rhGH) and exercise and assessed for muscle morphology and skeletal muscle tissue expression of GH and insulin-like growth factors (IGFs). Subjects initially underwent progressive resistance training for 14 weeks and were then randomized to receive either rhGH (0.02 mg/kg BW.day, sc) or PL while undertaking a further 10 weeks of training. Muscle samples were obtained at baseline and at 14 and 24 weeks. The mean (+/- SEM) cross-sectional areas of type I and II fibers were similar (type I, 3891 +/- 167 microns2; type II, 3985 +/- 200 microns2) at baseline and increased (P < 0.01) by 16.2 +/- 4.1% and 11.8 +/- 3.8%, respectively, after the initial 14-week training period. After treatment (weeks 14-24), two-way repeated measures ANOVA revealed a main effect of time for type I (P < 0.01) and type II fibers (P < 0.05), but no group effect or interaction. The increase in cross-sectional area for the PL group was significant (P = 0.01) for type I (11.5 +/- 3.6%) and approached significance (P = 0.06) for type II fibers (11.1 +/- 5.6%). For rhGH, the change in type I (6.3 +/- 5.9%) and II (7.1 +/- 5.2%) fiber area was not significant. No apparent change in tissue GH receptor, IGF-I, IGF-I receptor, IGF-II, or IGF-II receptor messenger ribonucleic acids occurred as a result of exercise after the 14-week pretreatment period or after treatment with rhGH or PL. These results indicate that rhGH administration in exercising elderly men does not augment muscle fiber hypertrophy or tissue GH-IGF expression and suggests that deficits in the GH-IGF-I axis with aging do not inhibit the skeletal muscle tissue response to training.

Aged↗
PubMed1996

Imprinting and expression of insulin-like growth factor-II and H19 in normal breast tissue and breast tumor.

Insulin-like growth factor (IGF)-II is a mitogenic peptide that has been reported to play an important role in the formation and growth of a variety of tumors. In most tissues, the IGF-II gene (IGF2) is parentally imprinted, with only the paternal allele being expressed. IGF2 messenger RNA (mRNA) and protein are overexpressed in some benign and malignant tumors. H19, a tumor suppressor gene located directly downstream from IGF2, is also genomically imprinted, but the paternal allele is silenced. It has been suggested that alterations in the imprinting of these two genes, which are located at chromosome 11p15.5, may lead to a malignant diathesis. We examined 18 fresh-frozen (FF) breast tumors with their adjacent normal breast tissue and 14 sets of paraffin-embedded formalin-fixed tissues for IGF2 and H19 gene expression and imprinting. IGF2 mRNA and H19 RNA could be quantitated in 15 of the 18 FF tumors. Although three of these tumors showed a > or = 2-fold increase in IGF2 expression when compared with the normal control tissues, the average abundance of IGF2 mRNA in 8 of 15 FF samples was < 50% that observed in the normal tissue. The expression of H19 RNA in these tumors was increased by > or = 2-fold in 5 tumors, but decreased by < or = 50% in 6 tumors when compared with normal adjacent tissue. By examining the ApaI and CA-repeat polymorphisms in the IGF2 gene, we found that the imprinting of IGF2 was maintained in all but 2 of the 17 informative subjects. H19 imprinting was maintained in all 18 informative fresh-frozen and paraffin-embedded formalin-fixed samples. Our data suggest that alterations in IGF2 and H19 gene expression and loss of imprinting do not occur reliably in breast cancer.

Alleles↗
PubMed1995

Renal growth hormone--insulin-like growth factor-I system in acute renal failure.

The renal growth hormone--insulin-like growth factor-I system in acute ischemic renal failure. Recovery from acute tubular necrosis (ATN) is accelerated by IGF-I therapy. Furthermore, the local renal growth hormone-IGF-I system may participate in the natural repair. We examined the IGF-I system in rat kidneys subjected to 60 minute ischemia compared to sham operated controls. Two days after injury, growth hormone receptor mRNA and IGF-I mRNA levels fell approximately 9 to 33% of control values. This was associated with a reduction in kidney immunoreactive IGF-I levels. In contrast, IGF-I receptor mRNA abundance was unchanged. However, plasma membrane IGF-I receptor binding on day 2 and day 7 was near double the control values (P < 0.01). Scatchard analysis revealed a near twofold increase in receptor number. Since receptor mRNA levels were unchanged, this implies receptor protein up-regulation. In contrast to unchanged IGF-I receptor mRNA levels, the abundance of mRNA levels of insulin-like growth factor binding proteins (IGFBP) -2, -3, -4 and -5 fell approximately 14 to 62% of control levels day 2 after injury (P < 0.05), suggesting reduced IGFBP production. Thus, the renal response to ischemic ATN, namely, low IGFBP mRNA levels and high IGF-I receptor number, may function to increase IGF-I bioavailability and thereby enhance the reparative actions of local and circulating IGF-I in ischemic ATN.

Acute Kidney Injury↗
PubMed1995

The human insulin-like growth factor-II promoter P1 is not restricted to liver: evidence for expression of P1 in other tissues and for a homologous promoter in baboon liver.

The human insulin-like growth factor (IGF)-II gene (IGF2) contains 4 different promoters (P1-P4), three of which (P2-P4) are homologous to the 3 promoters found in murine IGF-II genes. IGF-II is abundantly expressed in adult humans and primates, but IGF2 is only expressed in brain in adult rat and mouse. Previously, promoter P1 had been found exclusively in human adult liver but not in other human tissues or in rat or mouse liver. Although mouse liver does not express a homologue of human P1 mRNA, 5' "pseudo-exons" which are homologues of human exons 2 and 3 have been identified in murine IGF2. Based on the published DNA sequences of human exon 2 and the homologous murine pseudo-exon psi 1, we designed a 5'-oligonucleotide common to both human and murine IGF2 and a 3'-oligonucleotide primer from coding exon 7. We amplified specific cDNA from human and baboon livers, but no specific band was seen in rat or mouse liver. Chain-termination DNA sequencing confirmed that the P1 mRNA sequence from baboon liver shares 90% homology with human P1 mRNA in the 5' noncoding region (exons 2 and 3). Mature baboon IGF-II peptide is identical to human IGF-II, but there are 7 amino acid differences in the E region of the IGF-II prohormone. In humans, IGF-II mRNA transcripts containing P1 were also found in human myometrium and myomas. Our results demonstrate that the P1 promoter of the IGF-II gene is present in human and baboon adult liver, although it is absent from murine liver. In humans, promoter P1 is also utilized in tissues other than adult liver. We speculate that promoter P1 may be an important factor in persistent IGF-II synthesis.

Adult↗
PubMed1995

Insulin-like growth factor II in uterine smooth-muscle tumors: maintenance of genomic imprinting in leiomyomata and loss of imprinting in leiomyosarcomata.

Uterine leiomyosarcomata, malignant smooth-muscle tumors that may arise from existing leiomyomata or directly from the myometrium, have been shown to oversecrete insulin-like growth factor II (IGF-II). It has been shown recently that the IGF-II gene (IGF2) is maternally imprinted in both mice and humans. Only the paternal allele of IGF2 is usually expressed, except in adult liver and in the central nervous system in which biallelic expression is seen. Recently, loss of IGF2 imprinting has been reported in Wilms' tumor and in several other malignancies, and it has been suggested that biallelic expression of the gene leads to overexpression of IGF-II peptide and increased mitogenic activity. Using the ApaI restriction enzyme polymorphism in exon 9 of IGF2, we examined the expression of IGF2 in five informative uterine leiomyosarcomata and found that IGF2 was expressed biallelically in two tumors. In contrast, five samples of normal myometrium and six informative benign uterine leiomyomata showed monoallelic expression of IGF2. The incidence of heterozygosity at this locus was markedly lower in patients with leiomyosarcoma (6%) than in the healthy population (42% heterozygous; P < 0.01). H19, a gene that is imprinted in normal tissues, was expressed monoallelically in all informative normal and neoplastic uterine tumors. In contrast, the IGF-II receptor gene was expressed from both alleles in all tissues examined, confirming the finding that the human IGF-II receptor gene is not imprinted in humans. This study provides further evidence that relaxation of IGF2 genomic imprinting occurs not only in childhood tumors but also in adult-onset tumors, and it suggests a novel epigenetic mechanism for oncogenesis throughout life.

Base Sequence↗