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T H Vu

Publications and source records attributed to T H Vu.

At least 19 recordsLinked to original sources
PubMed2006

Cross-species clues of an epigenetic imprinting regulatory code for the IGF2R gene.

The epigenetic marks on the IGF2R gene that encodes a receptor responsible for IGF-II degradation consist of differentially methylated DNA in association with multiple modifications on the associated histones. We review these epigenetic marks across various species during the evolution of IGF2R imprinting. Both IGF2 and IGF2R genesare imprinted in the mammal lineage that diverged from Monotremata approximately 150 million years ago. While IGF2 is consistently imprinted in all mammals following its divergence, IGF2R imprinting disappears in the Euarchonta lineage, including human species, approximately 75 million years ago. Differential DNA methylation marks on the two parental alleles correlate with imprinting in all imprinted genes including IGF2R. While the DNA methylation marks in the IGF2R promoter region 1 (DMR1) correlate with IGF2R allelic expression, the DNA methylation marks in the intron region 2 (DMR2) fail to correlate with IGF2R imprinting status in a number of species. Human IGF2R and mouse neuronal Igf2r are not imprinted despite the presence of DMR2. We have noted that human IGF2R is not imprinted in more than 100 informative samples including various tumor tissues. Furthermore, opossum (Marsupialia) IGF2R is consistently imprinted despite the absence of DMR2. These lines of evidence indicate that DNA methylation marks in DMR2 are neither necessary nor sufficient for consistent imprinting of IGF2R across species. Histone modification marks, however, correlate more consistently with the tissue-specific and species-specific imprinting status of IGF2R in human and mouse. Acetylated histone H3 and H4 and methylated lysine 4 of H3 (H3-K4Me) associate with transcriptionally active alleles while tri-methylated lysine 9 of H3 (H3-K9Me3) marks the silenced alleles. In the mouse, an antisense non-coding transcript called Air is transcribed from DMR2 on the paternal allele, and this imprinted transcript plays a central role in Igf2r imprinting. Mouse Igf2r imprinting depends on an Air RNA while the existence of AIR in other species is unknown. Overall, DNA methylation, histone acetylation, and histone methylation play a vital role in coordinating IGF2R allelic expression across all species. Rare monoallelic or skewed allelic expression of human IGF2R and their biological importance warrants further rigorous study.

Animals↗
PubMed2002

Mitochondrial DNA depletion: mutations in thymidine kinase gene with myopathy and SMA.

BACKGROUND: The mitochondrial DNA (mtDNA) depletion syndrome (MDS) is an autosomal recessive disorder of early childhood characterized by decreased mtDNA copy number in affected tissues. Recently, MDS has been linked to mutations in two genes involved in deoxyribonucleotide (dNTP) metabolism: thymidine kinase 2 (TK2) and deoxy-guanosine kinase (dGK). Mutations in TK2 have been associated with the myopathic form of MDS, and mutations in dGK with the hepatoencephalopathic form. OBJECTIVES: To further characterize the frequency and clinical spectrum of these mutations, the authors screened 20 patients with myopathic MDS. RESULTS: No patient had dGK gene mutations, but four patients from two families had TK2 mutations. Two siblings were compound heterozygous for a previously reported H90N mutation and a novel T77M mutation. The other siblings harbored a homozygous I22M mutation, and one of them had evidence of lower motor neuron disease. The pathogenicity of these mutations was confirmed by reduced TK2 activity in muscle (28% to 37% of controls). CONCLUSIONS: These results show that the clinical expression of TK2 mutations is not limited to myopathy and that the myopathic form of MDS is genetically heterogeneous.

Child, Preschool↗
PubMed2001

Divergent evolution in M6P/IGF2R imprinting from the Jurassic to the Quaternary.

M6P/IGF2R imprinting first appeared approximately 150 million years ago following the divergence of prototherian from therian mammals. Although M6P/IGF2R is clearly imprinted in opossums and rodents, its imprint status in humans remains ambiguous. It is also still unknown if M6P/IGF2R imprinting was an ancestral mammalian epigenotype or if it evolved convergently. We report herein that M6P/IGF2R is imprinted in Artiodactyla, as it is in Rodentia and Marsupialia, but that it is not imprinted in Scandentia, Dermoptera and Primates, including ringtail lemurs and humans. These results are most parsimonious with a single ancestral origin of M6P/IGF2R imprinting followed by a lineage-specific disappearance of M6P/IGF2R imprinting in Euarchonta. The absence of M6P/IGF2R imprinting in extant primates, due to its disappearance from the primate lineage over 75 million years ago, demonstrates that imprinting at this locus does not predispose to human disease. Moreover, the divergent evolution of M6P/IGF2R imprinting predicts that the success of in vitro embryo procedures such as cloning may be species dependent.

Animals↗
PubMed2001

Myopathy with tubulin-reactive crystalline inclusions.

A 61-year-old man with muscle aches and persistently elevated serum creatine kinase had aggregates of randomly oriented, rhomboidal or rectangular protein crystalline inclusions in the sarcoplasm of type II fibers. Immunochemical studies showed strong reactivity of the inclusions to tubulin antibodies, suggesting that these unique crystalline inclusions may be a consequence of altered synthesis, processing, or degradation of tubulin.

Crystallization↗
PubMed2001

Tissue-specific alternate splicing of human telomerase reverse transcriptase (hTERT) influences telomere lengths during human development.

Direct genetic manipulations have shown that telomerase-mediated telomere elongation plays a key role in determining cellular replicative capacity and senescence. The mechanisms regulating the production of an active telomerase enzyme are still predominantly unknown, although roles for transcriptional control of hTERT, alternative-splicing of hTERT transcripts, and post-translational phosphorylation of hTERT protein have been advocated. Here we show that hTERT is alternatively spliced in specific patterns by different tissue types during human development. Alternative splicing often prohibits the expression of hTERT protein containing functional reverse transcriptase domains. In these instances, telomerase activity is absent, leading to shortening of telomeres. The specific pattern of hTERT mRNA variants in human development provides evidence that alternative splicing is non-random and participates in the regulation of telomerase activity.

Alternative Splicing↗
PubMed2001

Defects of intergenomic communication: autosomal disorders that cause multiple deletions and depletion of mitochondrial DNA.

Depletion and multiple deletions of mitochondrial DNA (mtDNA) have been associated with a growing number of autosomal diseases that have been classified as defects of intergenomic communication. MNGIE, an autosomal recessive disorder associated with mtDNA alterations is due to mutations in thymidine phosphorylase that may cause imbalance of the mitochondrial nucleotide pool. Subsequently, mutations in the mitochondrial proteins adenine nucleotide translocator 1, Twinkle, and polymerase gamma have been found to cause autosomal dominant progressive external ophthalmoplegia with multiple deletions of mtDNA. Uncovering the molecular bases of intergenomic communication defects will enhance our understanding of the mechanisms responsible for maintaining mtDNA integrity.

Chromosome Disorders↗
PubMed2001

Neuropathological features of mitochondrial disorders.

Genetic defects affecting the mitochondrial respiratory chain comprise an important cause of encephalomyopathies. Considering the structural complexity of the respiratory chain, its dual genetic control, and the numerous nuclear genes required for proper assembly of the enzyme complexes, the phenotypic heterogeneity is not surprising. From a neuropathological view point, application of in situ hybridization and immunohistochemistry to study the choroid plexus and brain-blood barrier in "prototypes" of mitochondrial encephalopathies have revealed alterations that we think are important in the pathogenesis of central nervous system dysfunction in these disorders. As the role of the blood-cerebrospinal fluid (CSF) and brain-blood barriers in mitochondrial encephalopathies is better understood, manipulation of their functions offers promises for therapeutic interventions.

Blood-Brain Barrier↗
PubMed2001

Don't mess with the matrix.

Extracellular matrix (ECM) remodeling is critical to morphogenesis and homeostasis. The identification of inactivating mutations in a gene encoding one of its modifying enzymes, matrix metalloproteinase 2 (MMP-2), in people with a hereditary disorder in which the bones disintegrate, represents the first genetic evidence that the proteolysis of the ECM mediates human growth and development. It also underscores the need for an intricate balance between breakdown and deposition of the ECM.

Abnormalities, Multiple↗
PubMed2001

Navajo neurohepatopathy: a mitochondrial DNA depletion syndrome?

Navajo neurohepatopathy (NNH) is an autosomal recessive disease of full-blooded Navajo children living in the Navajo Reservation of southwestern United States. Clinical features of NNH include peripheral and central nervous system involvement, acral mutilation, corneal scarring or ulceration, liver failure, and metabolic and immunologic derangement. The cause of NNH is unknown, but the clinical features of NNH are similar to those of patients with mitochondrial DNA (mtDNA) depletion. Therefore, we studied mtDNA concentration in the liver from 2 patients with NNH. Using histochemical, biochemical, and molecular techniques, we found evidence of mtDNA depletion, and we propose that the primary defect in NNH is in the nuclear regulation of mtDNA copy number.

Citrate (si)-Synthase↗
PubMed2001

Mitochondrial DNA depletion, near-fatal metabolic acidosis, and liver failure in an HIV-infected child treated with combination antiretroviral therapy.

A child with controlled human immunodeficiency virus infection presented with neurologic deterioration, lactic acidosis, and organic aciduria. Muscle biopsy revealed abnormal mitochondrial (mt) morphology, reduced mt enzyme activities, and mtDNA depletion. After adjustment of antiretroviral therapy to a regimen free of nucleoside analogs, marked improvement was seen in clinical status and mt abnormalities.

Acidosis↗
PubMed2000

Matrix metalloproteinase 9 and vascular endothelial growth factor are essential for osteoclast recruitment into developing long bones.

Bone development requires the recruitment of osteoclast precursors from surrounding mesenchyme, thereby allowing the key events of bone growth such as marrow cavity formation, capillary invasion, and matrix remodeling. We demonstrate that mice deficient in gelatinase B/matrix metalloproteinase (MMP)-9 exhibit a delay in osteoclast recruitment. Histological analysis and specialized invasion and bone resorption models show that MMP-9 is specifically required for the invasion of osteoclasts and endothelial cells into the discontinuously mineralized hypertrophic cartilage that fills the core of the diaphysis. However, MMPs other than MMP-9 are required for the passage of the cells through unmineralized type I collagen of the nascent bone collar, and play a role in resorption of mineralized matrix. MMP-9 stimulates the solubilization of unmineralized cartilage by MMP-13, a collagenase highly expressed in hypertrophic cartilage before osteoclast invasion. Hypertrophic cartilage also expresses vascular endothelial growth factor (VEGF), which binds to extracellular matrix and is made bioavailable by MMP-9 (Bergers, G., R. Brekken, G. McMahon, T.H. Vu, T. Itoh, K. Tamaki, K. Tanzawa, P. Thorpe, S. Itohara, Z. Werb, and D. Hanahan. 2000. Nat. Cell Biol. 2:737-744). We show that VEGF is a chemoattractant for osteoclasts. Moreover, invasion of osteoclasts into the hypertrophic cartilage requires VEGF because it is inhibited by blocking VEGF function. These observations identify specific actions of MMP-9 and VEGF that are critical for early bone development.

Animals↗
PubMed2000

Tissue-specific expression of antisense and sense transcripts at the imprinted Gnas locus.

The mouse Gnas gene encodes an important signal transduction protein, the alpha subunit of the stimulatory G protein, G(s). In humans, partial deficiency of G(s)alpha, the alpha subunit of G(s), results in the hormone-resistance syndrome pseudohypoparathyroidism type 1a. The mouse Gnas (and the human GNAS1) locus is transcribed from three promoter regions. Transcripts from P1, which encode Nesp55, are derived from the maternal allele only. Transcripts from P2 encode Xlalphas and are derived only from the paternal allele, while transcripts from P3 encode the alpha subunit and are from both parental alleles. The close proximity of reciprocal imprinting suggests the presence of important putative imprinting elements in this region. In this report, we demonstrate that the reciprocal imprinting occurs in normal tissues of interspecific (Mus spretus x C57BL/6) mice. Transcripts from P1 are most abundant in CNS (pons and medulla) in contrast to the more ubiquitous expression from P2 and P3. In the P1-P2 genomic region, we have identified an antisense transcript that starts 2.2 kb upstream of the P2 exon and spans the P1 region. While the P1 transcript is derived from the maternal allele, the P1-antisense (Gnas-as) is derived only from the paternal allele in most but not all tissues. Although both the Nesp55 region and the Gnas-as transcripts are present in cerebral cortex, adrenal, and spleen, Gnas-as is abundant in some tissues in which transcription from the Nesp55 region is negligible. Furthermore, the Nesp55 region transcripts remain strictly imprinted in tissues that lack Gnas-as. Our results suggest that multiple imprinting elements, including the unique Gnas-as, regulate the allelic expression of the Nesp55 region sense transcript.

Animals↗
PubMed2000

Allelic expression of the putative tumor suppressor gene p73 in human fetal tissues and tumor specimens.

p73, a proposed tumor suppressor, shares significant amino acid sequence homology with p53. However, p73 is rarely mutated in tumors but it has been suggested that p73 is monoallelically expressed in some tissues. This latter feature would predispose p73 to gene inactivation because a single genetic 'hit' or the loss of the expressed parental allele would leave the cell without p73 activity. We examined the allelic expression of p73 in normal fetal tissues and in ovarian cancer and Wilms' tumor. We found that p73 was biallelically expressed in all fetal tissues, except in brain, where differential expression of the two parental alleles was observed. Biallelic expression of p73 was also observed in paired samples of ovary cancer and Wilms' tumor. Loss of heterozygosity of p73 occurred at relatively low rates in tumors: one of 11 informative samples (9.1%) of ovarian cancer and two of 19 (10.1%) Wilms' tumors. These data demonstrate that p73 is biallelically expressed in most tissues, thus excluding genomic imprinting as a molecular mechanism to predispose to allelic inactivation of p73 in human tumors.

Alleles↗
PubMed2000

Symmetric and asymmetric DNA methylation in the human IGF2-H19 imprinted region.

The two contiguous IGF2 (human insulin-like growth factor II) and H19 genes are reciprocally imprinted in both human and mouse. In most tissues, IGF2 is transcribed only from the paternal chromosome while H19 is transcribed only from the maternal allele. The presence of a differential methylation region (DMR) on the two parental alleles at the 5' flanking region of H19 has been proposed to constitute the gametic imprint, which controls the reciprocal allelic expression of the two genes. Using bisulfite genomic sequencing, we have assessed the methylation status of cytosine (including 154 CpG sites) in six CpG-rich regions of the human IGF2-H19 genes. In a CpG island near promoter P3 of the IGF2 gene, more than 99.8% of all cytosines were converted to thymidine by sodium bisulfite mutagenesis, indicating that none of the CpGs was methylated. In the IGF2 exon 8-9 region, mosaic methylation of 56 CpG sites was observed in fetal tissues and in adult blood DNA. In contrast to the mosaic methylation of IGF2, the allelic methylation of the human H19 DMR was uniform. In the CpG region located 2 kb upstream (-2362 to -1911) of the H19 transcription site, all 25 CpG sites were completely methylated on only one parental allele. Uniform allele-specific methylation was also observed in the CpG island proximal to the H19 promoter (-711 to -290) with complete methylation of all 25 CpG sites in one parental allele. In contrast, the CpG region in the H19 promoter (-292 to +15) was mosaically methylated in all tissues. In addition, cytosine was methylated at three CpNpG and GpNpC sites on the top DNA strand and one CpNpG site on the bottom DNA strand from the fetal brain. The cytosines at CpG sites were methylated on both DNA strands (symmetric methylation) while cytosines at the CpNpG and GpNpC sites were methylated on only one DNA strand (asymmetric methylation). The asymmetric methylation was associated with tissue-specific disruption of H19 genomic imprinting in fetal brain.

Adult↗
PubMed2000

Proteinases in bone resorption: obvious and less obvious roles.

Bone resorption is critical for the development and the maintenance of the skeleton, and improper regulation of bone resorption leads to pathological situations. Proteinases are necessary for this process. In this review, we show that this need of proteinases is not only because they are required for the solubilization of bone matrix, but also because they are key components of the mechanism that determines where and when bone resorption will be initiated. Moreover, there are indications that proteinases may also determine whether resorption will be followed by bone formation. Some of the proteinases involved in these different steps of the resorption processes were recently identified, as for instance cathepsin K, MMP-9 (gelatinase B), and interstitial collagenase. However, there is also increasing evidence showing that the critical proteinase(s) may vary depending on the bone type or on other factors.

Bone Diseases↗
PubMed2000

Regulation of telomerase by alternate splicing of human telomerase reverse transcriptase (hTERT) in normal and neoplastic ovary, endometrium and myometrium.

Telomerase extends telomeric repeats at the ends of linear chromosomes, thereby prolonging the replicative capacity of cells. To investigate possible regulatory mechanisms of telomerase, we measured telomerase enzyme activity, human telomerase RNA (hTR) and human telomerase reverse transcriptase (hTERT) mRNA in normal and neoplastic ovary, endometrium and myometrium. Telomerase activity was detected in most malignancies and in normal endometrium but not in myometrial leiomyoma, normal myometrium or normal ovary. hTR was expressed in all tissue samples. hTERT mRNA was expressed in many tissue samples, and no tissue sample exhibited telomerase activity without expressing hTERT mRNA. However, the presence of hTR and hTERT mRNA was not sufficient for telomerase activity. Alternate splicing of hTERT produced mRNAs lacking critical reverse transcriptase (RT) motifs in both normal and neoplastic tissues. Only tissues expressing hTERT containing complete A and B RT motifs demonstrated telomerase activity. Finally, several normal ovarian tissues and myometrial leiomyomas lacked telomerase activity despite expressing hTR and hTERT containing complete A and B RT motifs. This was not seen in ovarian and myometrial malignancies, where the expression of hTR and hTERT containing complete A and B RT motifs was sufficient for telomerase activity. We conclude that in ovarian and uterine tissues, the presence of a functional telomerase complex is regulated at multiple levels, including hTERT transcription and alternative splicing of hTERT transcripts. The lack of telomerase activity in several normal but not malignant tissues expressing hTR and hTERT containing complete A and B RT motifs suggests that there are further mechanisms for suppressing telomerase activity downstream of hTERT transcription and mRNA splicing, and these mechanisms have been lost during neoplastic transformation.

Adenocarcinoma↗
PubMed2000

Analysis of mtDNA deletions in muscle by in situ hybridization.

We compared the distribution of deleted mitochondrial DNA (Delta-mtDNA) in skeletal muscle of a patient with autosomal recessive (AR) and another with autosomal dominant (AD) progressive external ophthalmoplegia (PEO) by in situ hybridization (ISH). The patients studied had similar numbers of fibers deficient in cytochrome c oxidase (COX) activity (13.6% and 12.8%) and fibers with mitochondrial proliferation (5.5% and 5.3%). ISH suggested that each COX-deficient fiber contained a single species of Delta-mtDNA. Most deletions ablated the region between the genes encoding adenosine triphosphate (ATP) synthase subunit 8 and cytochrome b. Fibers that appeared to be depleted of mtDNA were also present. We conclude that muscle from patients with autosomally inherited PEO contains not only Delta-mtDNA but also focal depletion of mtDNA and that the distribution of these mtDNA defects appears to be similar. These changes most likely represent the common consequence of whatever genetic factors are responsible for the generation of Delta-mtDNA.

Adult↗