Diagnostic Accuracy and Scope of Intraoperative Transoral Ultrasound and Transoral Ultrasound-Guided Fine-Needle Aspiration of Retropharyngeal Masses

The use of transoral sonography-guided fine-needle aspiration for intraoperative localization of retropharyngeal masses has been described by Fornage et al. The purpose of this study was to assess the accuracy of this technique. We reviewed the images and medical records of 26 patients with a retropharyngeal lesion suspicious for a metastatic lymph node of Rouviere identified on CT and/or PET/CT. There were 14 patients with a history of thyroid cancer, 7 with mucosal squamous cell carcinoma, 1 with renal cell carcinoma, 1 with parotid acinic cell cancer, 1 with metastatic colon adenocarcinoma, and 2 with no history of cancer. Intraoperative transoral sonography was performed using a commercially available endovaginal transducer. A transoral sonography-guided fine-needle aspiration was performed with a 25-cm-long 20-ga Chiba needle through a needle guide attached to the transducer shaft. Cytopathologic results were categorized as malignant, benign, or nondiagnostic. Transoral sonography and transoral sonography-guided fine-needle aspiration were performed in all patients. A diagnostic specimen was obtained in 25 of 26 (96%) patients with a 100% overall accuracy. Twelve patients underwent subsequent transoral resection of the retropharyngeal mass. In each patient, surgical pathology confirmed the fine-needle aspiration biopsy result. In 4 patients, transoral sonography-guided injection of methylene blue was used to facilitate intraoperative localization of the metastatic retropharyngeal mass. Transoral sonography and transoral sonography-guided fine-needle aspiration of suspicious masses in the retropharyngeal space are highly accurate procedures for identification and cytologic evaluation of benign and metastatic lymph nodes of Rouviere and for presurgical localization.

Role of vitamin D in cell-cell interaction of fetal endothelial progenitor cells and umbilical cord endothelial cells in a preeclampsia-like model

Maternal endothelial dysfunction is a cental feature of preeclampsia (PE), a hypertensive disorder of pregnancy. Factors in the maternal circulation are thought to contribute to this endothelial dysfunction. Although understudied, factors in the fetal circulation may influence fetal endothelial cell interactions with endothelial progenitor cells as critical steps in placental angiogenesis. We hypothesize that cell-cell interactions that are important for pregnancy health are impaired by fetal serum from PE pregnancies and that 1,25(OH)₂-vitamin D₃ attenuates the negative effects of this serum on cell function. We tested the ability of fetal cord blood-derived endothelial progenitor cells [endothelial colony-forming cells (ECFCs)] to invade into established monolayers and capillary tubule-like structures of human fetal umbilical venous endothelial cells (HUVECs), while in the presence/absence of fetal cord serum from uncomplicated or PE pregnancies, and tested the ability of 1,25(OH)₂-vitamin D₃ to modulate the serum-mediated effects. PE cord serum reduced the invasion of fetal ECFCs into HUVEC monolayers or tubule networks. Vitamin D attenuated these effects of PE fetal serum on endothelial functional properties. Immunocytochemical studies revealed involvement of VE-cadherin contacts in interactions between ECFCs and mature fetal endothelial cells. PE cord serum reduces the ability of fetal endothelial progenitor cells to incorporate into fetal endothelial cell networks. Physiologic concentrations of vitamin D reverse these PE serum-mediated effects. These data appear consistent with lines of evidence that vitamin D has antipreeclampsia effects.

Solitary Parathyroid Adenoma Localization in Technetium Tc99m Sestamibi SPECT and Multiphase Multidetector 4D CT

BACKGROUND AND PURPOSE

Minimally invasive parathyroid surgery relies critically on image guidance, but data comparing the efficacy of various imaging modalities are scarce. Our aim was to perform a blinded comparison of the localizing capability of technetium Tc99m sestamibi SPECT, multiphase multidetector 4D CT, and the combination of these 2 modalities (technetium Tc99m sestamibi SPECT + multiphase multidetector 4D CT).

MATERIALS AND METHODS

We reviewed the records of 31 (6 men, 25 women; median age, 56 years) consecutive patients diagnosed with biochemically confirmed primary hyperparathyroidism between November 2009 and March 2010 who underwent preoperative technetium Tc99m sestamibi SPECT and multiphase multidetector 4D CT performed on the same scanner with pathologic confirmation by resection of a single parathyroid adenoma. Accuracy was determined separately for localization to the correct side and quadrant using surgical localization as the standard of reference.

RESULTS

Surgical resection identified 14 left and 17 right parathyroid adenomas and 2 left inferior, 12 left superior, 11 right inferior, and 6 right superior parathyroid adenomas. For left/right localization, technetium Tc99m sestamibi SPECT achieved an accuracy of 93.5% (29 of 31), multiphase multidetector 4D CT achieved 96.8% accuracy (30 of 31), and technetium Tc99m sestamibi SPECT + multiphase multidetector 4D CT achieved 96.8% accuracy (30 of 31). For quadrant localization, technetium Tc99m sestamibi SPECT accuracy was 67.7% (21 of 31), multiphase multidetector 4D CT accuracy was 87.1% (27 of 31), and technetium Tc99m sestamibi SPECT + multiphase multidetector 4D CT accuracy was 93.5% (29 of 31). Reader diagnostic confidence was consistently ranked lowest for technetium Tc99m sestamibi SPECT and highest for technetium Tc99m sestamibi SPECT + multiphase multidetector 4D CT.

CONCLUSIONS

For left/right localization of parathyroid adenomas, all modalities performed equivalently. For quadrant localization, technetium Tc99m sestamibi SPECT + multiphase multidetector 4D CT is superior to technetium Tc99m sestamibi SPECT.

Minor changes in the macrocyclic ligands but major consequences on the efficiency of gold nanoparticles designed for radiosensitization

Many studies have been devoted to adapting the design of gold nanoparticles to efficiently exploit their promising capability to enhance the effects of radiotherapy. In particular, the addition of magnetic resonance imaging modality constitutes an attractive strategy for enhancing the selectivity of radiotherapy since it allows the determination of the most suited delay between the injection of nanoparticles and irradiation. This requires the functionalization of the gold core by an organic shell composed of thiolated gadolinium chelates. The risk of nephrogenic systemic fibrosis induced by the release of gadolinium ions should encourage the use of macrocyclic chelators which form highly stable and inert complexes with gadolinium ions. In this context, three types of gold nanoparticles (Au@DTDOTA, Au@TADOTA and Au@TADOTAGA) combining MRI, nuclear imaging and radiosensitization have been developed with different macrocyclic ligands anchored onto the gold cores. Despite similarities in size and organic shell composition, the distribution of gadolinium chelate-coated gold nanoparticles (Au@TADOTA-Gd and Au@TADOTAGA-Gd) in the tumor zone is clearly different. As a result, the intravenous injection of Au@TADOTAGA-Gd prior to the irradiation of 9L gliosarcoma bearing rats leads to the highest increase in lifespan whereas the radiophysical effects of Au@TADOTAGA-Gd and Au@TADOTA-Gd are very similar.

Identifying multi-locus chromatin contacts in human cells using tethered multiple 3C

Background

Several recently developed experimental methods, each an extension of the chromatin conformation capture (3C) assay, have enabled the genome-wide profiling of chromatin contacts between pairs of genomic loci in 3D. Especially in complex eukaryotes, data generated by these methods, coupled with other genome-wide datasets, demonstrated that non-random chromatin folding correlates strongly with cellular processes such as gene expression and DNA replication.

Results

We describe a genome architecture assay, tethered multiple 3C (TM3C), that maps genome-wide chromatin contacts via a simple protocol of restriction enzyme digestion and religation of fragments upon agarose gel beads followed by paired-end sequencing. In addition to identifying contacts between pairs of loci, TM3C enables identification of contacts among more than two loci simultaneously. We use TM3C to assay the genome architectures of two human cell lines: KBM7, a near-haploid chronic leukemia cell line, and NHEK, a normal diploid human epidermal keratinocyte cell line. We confirm that the contact frequency maps produced by TM3C exhibit features characteristic of existing genome architecture datasets, including the expected scaling of contact probabilities with genomic distance, megabase scale chromosomal compartments and sub-megabase scale topological domains. We also confirm that TM3C captures several known cell type-specific contacts, ploidy shifts and translocations, such as Philadelphia chromosome formation (Ph+) in KBM7. We confirm a subset of the triple contacts involving the IGF2-H19 imprinting control region (ICR) using PCR analysis for KBM7 cells. Our genome-wide analysis of pairwise and triple contacts demonstrates their preference for linking open chromatin regions to each other and for linking regions with higher numbers of DNase hypersensitive sites (DHSs) to each other. For near-haploid KBM7 cells, we infer whole genome 3D models that exhibit clustering of small chromosomes with each other and large chromosomes with each other, consistent with previous studies of the genome architectures of other human cell lines.

Conclusion

TM3C is a simple protocol for ascertaining genome architecture and can be used to identify simultaneous contacts among three or four loci. Application of TM3C to a near-haploid human cell line revealed large-scale features of chromosomal organization and multi-way chromatin contacts that preferentially link regions of open chromatin.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1236-7) contains supplementary material, which is available to authorized users.

Loss of IGF2 imprinting is associated with abrogation of long-range intrachromosomal interactions in human cancer cells

Nuclear architecture and chromatin geography are important factors in the regulation of gene expression, as these components may play a vital epigenetic role both in normal physiology as well as in the initiation and progression of malignancies. Using a modification of the chromosome conformation capture (3C) technique, we examined long-range chromatin interactions of the imprinted human IGF2 gene. We demonstrate that numerous intrachromosomal interactions occur along both parental alleles in normal tissues, where the IGF2 is paternally expressed, as well as in normal liver where gene expression is biallelic. Long-range and allele-specific interactions occur between the IGF2/H19 imprinting control region-1 (ICR1) and ICR2, a region which regulates an imprinted gene cluster nearly a megabase distant from IGF2. Loss of genomic imprinting is a common epigenetic event in cancer, and long-range interactions have not been examined in malignant cells. In cancer cell lines in which IGF2 imprinting is maintained (MOI), essentially all of the 3C interactions seen in normal cells were preserved. However, in cells in which IGF2 imprinting was lost (LOI), nearly all of the long-range chromatin interactions involving IGF2 were abrogated. A three-dimensional computer model depicts the physical interactions between the IGF2 promoter and ICR1 in MOI cells, while the model of LOI lung cancer cells is flattened with few long-range interactions. This dramatic change in the three-dimension configuration of the chromatin at the IGF2 locus in LOI cancer cells suggests that the loss of imprinting may lead to a variety of changes in gene expression in addition to changes in IGF2 transcription.

A complex deoxyribonucleic acid looping configuration associated with the silencing of the maternal Igf2 allele

Alternate interactions between the H19 imprinting control region (ICR) and one of the two Igf2 differentially methylated regions has been proposed as a model regulating the reciprocal imprinting of Igf2 and H19. To study the conformation of this imprint switch, we performed a systematic structural analysis across the 140 kb of the mouse Igf2-H19 region, which includes enhancers located both between the two genes as well as downstream of H19, by using a scanning chromosome conformation capture (3C) technique. Our results suggest that on the active paternal Igf2 allele, the various enhancers have direct access to the Igf2 promoters, whereas the imprinted silent maternal Igf2 allele assumes a complex three-dimensional knotted loop that keeps the enhancers away from the Igf2 promoters and allows them to interact with the H19 promoter. This complex DNA looping of the maternal allele is formed by interactions involving differentially methylated region 1, the ICR, and enhancers. Binding of CTC-binding factor to the maternal, unmethylated ICR in conjunction with the presence of multicomplex components including interchromosomal interactions, create a barrier blocking the access of all enhancers to Igf2, thereby silencing the maternal Igf2. This silencing configuration exists in newborn liver, mouse embryonic fibroblast, and embryonic stem cells and persists during mitosis, conferring a mechanism for epigenetic memory.

Correction of aberrant imprinting of IGF2 in human tumors by nuclear transfer-induced epigenetic reprogramming

Loss of genomic imprinting of insulin-like growth factor II (IGF2) is a hallmark of many human neoplasms. We attempted to correct this aberrant epigenotype by transferring nuclei from human tumor cells that showed loss of IGF2 imprinting into enucleated mouse and human fibroblasts that had maintained normal IGF2 imprinting. After nuclear transfer, the abnormal biallelic expression of IGF2 in tumor nuclei transiently converted to normal monoallelic imprinted expression in the reconstructed diploid cells. In tetraploid hybrid cells, however, normal IGF2 imprinting was permanently restored in the tumor genome. Inhibition of the synthesis of putative trans imprinting factors with cycloheximide led to loss of IGF2 imprinting in normal cultured fibroblasts, suggesting that normal cells produce proteins that act in trans to induce or maintain genomic imprinting. These data demonstrate that an abnormal tumor epigenotype can be corrected by in vitro reprogramming, and suggest that loss of imprinting is associated with the loss of activity of non-CTCF trans imprinting factor(s) that are either inactivated or mutated in tumors.

CTCF mediates interchromosomal colocalization between Igf2/H19 and Wsb1/Nf1

Gene transcription may be regulated by remote enhancer or insulator regions through chromosome looping. Using a modification of chromosome conformation capture (3C) and fluorescence in situ hybridization, we found that one allele of the insulin-like growth factor 2 (Igf2)/H19 imprinting control region (ICR) on chromosome 7 colocalized with one allele of Wsb1/Nf1 on chromosome 11. Omission of CCCTC-binding factor (CTCF) or deletion of the maternal ICR abrogated this association and altered Wsb1/Nf1 gene expression. These findings demonstrate that CTCF mediates an interchromosomal association, perhaps by directing distant DNA segments to a common transcription factory, and the data provide a model for long-range allele-specific associations between gene regions on different chromosomes that suggest a framework for DNA recombination and RNA trans-splicing.

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.

Defects of intergenomic communication: where do we stand?

An expanding number of autosomal diseases has been associated with mitochondrial DNA (mtDNA) depletion and multiple deletions. These disorders have been classified as defects of intergenomic communication because mutations of the nuclear DNA are thought to disrupt the normal cross-talk that regulates the integrity and quantity of mtDNA. In 1989, autosomal dominant progressive external ophthalmoplegia with multiple deletions of mitochondrial DNA was the first of these disorders to be identified. Two years later, mtDNA depletion syndrome was initially reported in infants with severe hepatopathy or myopathy. The causes of these diseases are still unclear, but genetic linkage studies have identified three chromosomal loci for AD-PEO. Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE), an autosomal recessive disorder associated with both mtDNA depletion and multiple deletions, is now known to be due to loss-of-function mutations in the gene encoding thymidine phosphorylase. Increased plasma thymidine levels in MNGIE patients suggest that imbalanced nucleoside and nucleotide pools in mitochondria may lead to impaired replication of mtDNA. Future research will certainly lead to the identification of additional genetic causes of intergenomic communication defects and will likely provide insight into the normal "dialogue" between the two genomes.

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.

Promoter-restricted histone code, not the differentially methylated DNA regions or antisense transcripts, marks the imprinting status of IGF2R in human and mouse

Imprinting of the mouse Igf2r depends upon an intronic differentially methylated DNA region (DMR) and the presence of the Air antisense transcript. However, biallelic expression of mouse Igf2r in brain occurs despite the presence of Air, and biallelic expression of human IGF2R in peripheral tissues occurs despite the presence of an intronic DMR. We examined histone modifications throughout the mouse and human Igf2r/IGF2R using chromatin immuno-precipitation (ChIP) assays in combination with quantitative real time PCR. Methylation of Lys4 and Lys9 of histone H3 in the promoter regions marks the active and silenced alleles, respectively. We measured di- and tri-methyl Lys4 and Lys9 across the Igf2r and Air promoters. While both di- and tri-methyl Lys4 marked the active Igf2r and the active Air allele, tri-methyl Lys9, but not di-methyl Lys9, marked the suppressed Air allele. We show here that enrichment of parental allele-specific histone modifications in the promoter region, rather than the presence of DNA methylation or antisense transcription, correctly identifies the tissue- and species- specific imprinting status of Igf2r/IGF2R. We discuss these findings in light of recent progress in identifying specific components of the epigenetic marks in imprinted genes.

Epigenetic regulation of Igf2/H19 imprinting at CTCF insulator binding sites

The mouse insulin-like growth factor II (Igf2) and H19 genes are located adjacent to each other on chromosome 7q11-13 and are reciprocally imprinted. It is believed that the allelic expression of these two genes is regulated by the binding of CTCF insulators to four parent-specific DNA methylation sites in an imprinting control center (ICR) located between these two genes. Although monoallelically expressed in peripheral tissues, Igf2 is biallelically transcribed in the CNS. In this study, we examined the allelic DNA methylation and CTCF binding in the Igf2/H19 imprinting center in CNS, hypothesizing that the aberrant CTCF binding as one of the mechanisms leads to biallelic expression of Igf2 in CNS. Using hybrid F1 mice (M. spretus males x C57BL/6 females), we showed that in CNS, CTCF binding sites in the ICR were methylated exclusively on the paternal allele, and CTCF bound only to the unmethylated maternal allele, showing no differences from the imprinted peripheral tissues. Among three other epigenetic modifications examined, histone H3 lysine 9 methylation correlated well with Igf2 allelic expression in CNS. These results suggest that CTCF binding to the ICR alone is not sufficient to insulate the Igf2 maternal promoter and to regulate the allelic expression of the gene in the CNS, thus challenging the aberrant CTCF binding as a common mechanism for lack of Igf2 imprinting in CNS. Further studies should be focused on the identification of factors that are involved in histone methylation and CTCF-associated factors that may be needed to coordinate Igf2 imprinting.

Epigenetic regulation of the taxol resistance-associated gene TRAG-3 in human tumors

TRAG-3, originally identified as a taxol resistance-associated gene from an ovarian carcinoma cell line, is upregulated in many human tumors. Like many tumor antigens, TRAG-3 mRNA is not detectable or is expressed at very low levels in normal fetal and adult human tissues except for testis, where TRAG-3 mRNA transcripts are detected abundantly. TRAG-3 mRNA is frequently overexpressed in tumors but is rarely detected in adjacent normal tissues. To delineate the transcriptional regulation of this tumor antigen, we cloned and sequenced the TRAG-3 promoter. A 539-base pair fragment upstream of the initiation site, which contains two unusual CT repeat stretches, was sufficient to drive the maximum activity of a luciferase reporter gene. Sodium bisulfite sequencing of genomic DNA revealed that the amount of DNA methylation in exon 2 and in the promoter regions is inversely correlated with gene expression. In normal tissues, TRAG-3 is hypermethylated and is thus transcriptionally silenced. In those tumors where TRAG-3 is actively transcribed, the TRAG-3 promoter and exon 2 are hypomethylated. Treatment of a TRAG-3-silenced cell line H23 with the demethylating reagent 5-aza-cytosine reduced DNA methylation and induced TRAG-3 expression in a dose-dependent manner. These results indicate that DNA demethylation is an important epigenetic mechanism that regulates the TRAG-3 tumor antigen in human tumors.

Activating and silencing histone modifications form independent allelic switch regions in the imprinted Gnas gene

Activation and suppression of gene transcription is tightly controlled by epigenetic modifications. The imprinted Gnas1 gene region contains closely juxtaposed maternally expressed (Nesp) and paternally expressed (Nespas, Gnasxl, Exon 1A) transcripts, providing a unique opportunity to study how epigenetic modifications change in nucleosomes from active to silenced promoters. Using 30 polymorphic sites across the Gnas1 gene region in (C57BL/6JxMus spretus) F(1) mice and chromatin immunoprecipitation (ChIP) assays we identified two allelic switch regions (ASRs) that mark boundaries of epigenetic information. We show that activating signals (histone acetylation and methylation of H3 Lys4) and silencing signals (histone methylation of H3 Lys9 and DNA methylation) segregate independently across the ASRs and suggest that these ASRs allow the transcriptional elongation to proceed through the silenced domain of nearby imprinted promoters. We discuss these findings in light of recent progress in the conceptualization of nucleosome remodeling during transcriptional elongation and in the development of histone code.

The histone code regulating expression of the imprinted mouse Igf2r gene

The mouse IGF-II receptor (Igf2r) and its antisense transcript Air are reciprocally imprinted in most normal tissues. Several mechanisms have been hypothesized to explain Igf2r-Air imprinting, including Igf2r silencing by Air, and transcriptional repression of Igf2r-Air by two differentially methylated regions (DMR1 and DMR2). We employed Mus musculus x Mus spretus interspecific mice and chromatin immunoprecipitation (ChIP) to investigate allele-specific histone modifications in the two DMRs. We show that, in both DMRs, the active alleles of both Igf2r, and Air are associated with acetylated histones (H3, and H4), acetyl lysine 9 of histone H3 (H3 K9-Ac), and methyl lysine 4 of histone H3 (H3 K4-Me). The silenced alleles are associated with methylated DNA, deacetylated H3 K9, and unmethylated H3 K4. Allele-specific histone modifications are present in the DMR2 that is established in the gametes and represents the DNA gametic-imprint of the Igf2r. In the DMR2 from liver, kidney, and central nervous system tissues, H3 K9 methylation is associated exclusively with the silenced allele, and H3 S10 phosphorylation with the active alleles. Treatment of fibroblast cells with 5-aza-deoxycytidine and/or Trichostatin A led to partial reactivation of the silenced allele, which correlates with biallelic histone acetylation. In central nervous system, despite the presence of imprinted Air transcripts, biallelic expression of Igf2r occurs. The tissue-specific relaxation of Igf2r imprinting correlates with biallelic histone acetylation, and biallelic H3 K4 methylation in the promoter region of Igf2r (DMR1). We propose a model of the histone code for Igf2r, and Air imprinting that defines histone modifications specific for the putative gametic imprint DMR2, and explains the tissue-specific imprinting of Igf2r in the mouse and the absence of IGF2R imprinting in human.

CTCF binding at the insulin-like growth factor-II (IGF2)/H19 imprinting control region is insufficient to regulate IGF2/H19 expression in human tissues

The adjacent IGF2 and H19 genes are imprinted in most normal mouse and human tissues, but imprinting is often lost in tumors. Mouse models suggest that parental-allele specific CCCTC-binding factor (CTCF) binding at the IGF2/H19 imprinting control region (ICR) regulates the expression of these two genes. Using chromatin immunoprecipitation and PCR, we show that in several normal and neoplastic human tissues, CTCF consistently binds unmethylated ICR elements, but CTCF binding does not result in predictable gene expression. In the fetal brain, CTCF binding is monoallelic and specific for the unmethylated ICR, yet IGF2/H19 expression is biallelic. In osteosarcoma tumors, aberrant methylation of the IGF2/H19 ICR results in equally aberrant CTCF binding, yet expression of these genes does not correlate with CTCF binding. This is the first description of chromatin immunoprecipitation for CTCF binding at the human IGF2/H19 ICR, and the results demonstrate that CTCF binding at the IGF2/H19 ICR is insufficient to regulate the expression of IGF2/H19 in many human tissues.

Loss of imprinting of IGF2 sense and antisense transcripts in Wilms' tumor

Human insulin-like growth factor II gene (IGF2) is overexpressed, and its imprinting is disrupted in many tumors, including Wilms' tumor. A transcript that is antisense to IGF2, IGF2-antisense (IGF2-AS), is transcribed from within IGF2 in a reverse orientation. This transcript is also maternally imprinted and overexpressed in Wilms' tumor. IGF2-AS was detected as a 2.2 kb mRNA in Hep 3B cells by Northern blotting, and it encodes a putative 168 amino acid peptide. An alternative splicing mRNA observed predominantly in adult liver encodes an additional putative 199 amino acid peptide. We have examined the expression of IGF2 and IGF2-AS in normal tissue, breast and ovarian tumors, and 25 informative, well-characterized Wilms' tumors and determined the relationship between IGF2 and IGF2-AS imprinting. IGF2-AS was expressed at levels comparable with IGF2 sense expression derived from promoters P1 and P2 in normal tissue and in breast, ovarian, and Wilms' tumor tissues. In Wilms' tumors that demonstrate maintenance of imprinting of IGF2, IGF2-AS was imprinted. In contrast, in tumors which demonstrate LOI of IGF2, only two of six tumors showed loss of imprinting of IGF2-AS, whereas four of six tumors demonstrated maintenance of imprinting for IGF2-AS. The discrepancy between IGF2 and IGF2-AS loss of imprinting in some tumors demonstrates the control complexity of the imprinting status of the various transcripts derived from the IGF2 gene.

Loss of imprinting of IGF2 and H19 in osteosarcoma is accompanied by reciprocal methylation changes of a CTCF-binding site

The adjacent insulin-like growth factor 2 (IGF2) and H19 genes are imprinted in most normal human tissues, but imprinting is often lost in tumors. The mechanisms involved in maintenance of imprinting (MOI) and loss of imprinting (LOI) are unresolved. We show here that osteosarcoma (OS) tumors with IGF2/H19 MOI exhibit allele-specific differential methylation of a CTCF-binding site upstream of H19. LOI of IGF2 or H19 in OS occurs in a mutually exclusive manner, and occurs with monoallelic expression of the other gene. Bisulfite sequencing reveals IGF2 LOI occurs with biallelic CpG methylation of the CTCF-binding site, while H19 LOI occurs with biallelic hypomethylation of this site. Our data demonstrate that IGF2 LOI and H19 LOI are accompanied by reciprocal methylation changes at a critical CTCF-binding site. We propose a model in which incomplete gain or loss of methylation at this CTCF-binding site during tumorigenesis explains the complex and often conflicting expression patterns of IGF2 and H19 in tumors.

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.

An imprinted PEG1/MEST antisense expressed predominantly in human testis and in mature spermatozoa

PEG1 (or MEST) is an imprinted gene located on human chromosome 7q32 that is expressed predominantly from the paternal allele. In the mouse, Peg1/Mest is associated with embryonic growth and maternal behavior. Human PEG1 is transcribed from two promoters; the transcript from promoter P1 is derived from both parental alleles, and the transcript from P2 is exclusively from the paternal allele. We characterized the P1 and P2 transcripts in various normal and neoplastic tissues. In the normal tissues, PEG1 was transcribed from both promoters P1 and P2, whereas in six of eight neoplastic tissues, PEG1 was transcribed exclusively from promoter P1. Bisulfite sequencing demonstrated high levels of CpG methylation in the P2 region of DNA from a lung tumor. In the region between P1 and P2, we identified a novel transcript, PEG1-AS, in an antisense orientation to PEG1. PEG1-AS is a spliced transcript and was detected as a strong 2.4-kilobase band on a Northern blot. PEG1-AS and PEG1 P2-sense transcript were expressed exclusively from the paternal allele. Fragments of DNA from within the 1.5-kilobase region between PEG1-AS and the P2 exon were ligated to a pGL3 luciferase reporter vector and transfected into NCI H23 cells. This DNA exhibited strong promoter activity in both the sense and antisense directions, indicating that PEG1-AS and P2 exon share a common promoter region. Treatment of the transfected DNA fragments with CpG methylase abolished the promoter activity. Of interest, PEG1-AS was expressed predominantly in testis and in mature motile spermatozoa, indicating a possible role for this transcript in human sperm physiology and fertilization.

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.

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.

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.

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.

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.

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.

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.

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.

Allele-specific histone acetylation accompanies genomic imprinting of the insulin-like growth factor II receptor gene

The mouse insulin-like growth factor II receptor (Igf2r) gene encodes two reciprocally imprinted RNA transcripts: paternally imprinted Igf2r sense and maternally imprinted Igf2r antisense. Although DNA methylation has been implicated in the initiation and maintenance of genomic imprinting, acetylation of core histones has recently been appreciated as another important factor that regulates gene expression. To determine whether histone acetylation participates in the regulation of Igf2r imprinting, we examined the relative abundance of acetylated histones in interspecific mice (M. spretus x C57BL/6). Oligonucleosomes derived from liver were immunoprecipitated with acetyl-histone antiserum and were analyzed for the allelic distribution of DNA from the region of the sense and antisense Igf2r promoters. In nucleosomes associated with the Igf2r sense promoter, histone acetylation was demonstrated on the maternal allele, which is transcriptionally active. There was much less histone acetylation on the suppressed paternal allele. In nucleosomes associated with the Igf2r antisense promoter, the active paternal allele was heavily acetylated, whereas the suppressed maternal allele was underacetylated. Treatment of cultured fibroblasts with the histone deacetylase inhibitor Trichostatin A induces partial relaxation of genomic imprinting as well as decreased DNA methylation of both Igf2r sense and antisense promoters. These results demonstrate that increases in histone acetylation can lead to decreased DNA methylation, thereby modulating the regulation of the imprinted expression of Igf2r sense and antisense transcripts.

Comparative genome analysis of the mouse imprinted gene impact and its nonimprinted human homolog IMPACT: toward the structural basis for species-specific imprinting

Mouse Impact is a paternally expressed gene encoding an evolutionarily conserved protein of unknown function. Here we identified IMPACT, the human homolog of Impact, on chromosome 18q11. 2-12.1, a region syntenic to the mouse Impact locus. IMPACT was expressed biallelically in brain and in various tissues from two informative fetuses and in peripheral blood from an informative adult. To reveal the structural basis for the difference in allelic expression between the two species, we elucidated complete genome sequences for both mouse Impact ( approximately 38 kb) and human IMPACT ( approximately 30 kb). Sequence comparison revealed that the two genes share a well-conserved exon-intron organization but bear significantly different CpG islands. The mouse island lies in the first intron and contains characteristic tandem repeats. Furthermore, this island serves as a differentially methylated region (DMR) consisting of a hypermethylated maternal allele and an unmethylated paternal allele. Intriguingly, this intronic island is missing from the nonimprinted human IMPACT, whose sole CpG island spans the first exon, lacks any apparent repeats, and escapes methylation on both chromosomes. These results suggest that the intronic DMR plays a role in the imprinting of Impact.

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.

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.

Mitochondrial neurogastrointestinal encephalomyopathy: an autosomal recessive disorder due to thymidine phosphorylase mutations

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is an autosomal recessive disorder defined clinically by severe gastrointestinal dysmotility; cachexia; ptosis, ophthalmoparesis, or both; peripheral neuropathy; leukoencephalopathy; and mitochondrial abnormalities. The disease is caused by mutations in the thymidine phosphorylase (TP) gene. TP protein catalyzes phosphorolysis of thymidine to thymine and deoxyribose 1-phosphate. We identified 21 probands (35 patients) who fulfilled our clinical criteria for MNGIE. MNGIE has clinically homogeneous features but varies in age at onset and rate of progression. Gastrointestinal dysmotility is the most prominent manifestation, with recurrent diarrhea, borborygmi, and intestinal pseudo-obstruction. Patients usually die in early adulthood (mean, 37.6 years; range, 26-58 years). Cerebral leukodystrophy is characteristic. Mitochondrial DNA (mtDNA) has depletion, multiple deletions, or both. We have identified 16 TP mutations. Homozygous or compound heterozygous mutations were present in all patients tested. Leukocyte TP activity was reduced drastically in all patients tested, 0.009 +/- 0.021 micromol/hr/mg (mean +/- SD; n = 16), compared with controls, 0.67 +/- 0.21 micromol/hr/mg (n = 19). MNGIE is a recognizable clinical syndrome caused by mutations in thymidine phosphorylase. Severe reduction of TP activity in leukocytes is diagnostic. Altered mitochondrial nucleoside and nucleotide pools may impair mtDNA replication, repair, or both.

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.

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.

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.

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.

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.

VEGF couples hypertrophic cartilage remodeling, ossification and angiogenesis during endochondral bone formation

Hypertrophic chondrocytes in the epiphyseal growth plate express the angiogenic protein vascular endothelial growth factor (VEGF). To determine the role of VEGF in endochondral bone formation, we inactivated this factor through the systemic administration of a soluble receptor chimeric protein (Flt-(1-3)-IgG) to 24-day-old mice. Blood vessel invasion was almost completely suppressed, concomitant with impaired trabecular bone formation and expansion of hypertrophic chondrocyte zone. Recruitment and/or differentiation of chondroclasts, which express gelatinase B/matrix metalloproteinase-9, and resorption of terminal chondrocytes decreased. Although proliferation, differentiation and maturation of chondrocytes were apparently normal, resorption was inhibited. Cessation of the anti-VEGF treatment was followed by capillary invasion, restoration of bone growth, resorption of the hypertrophic cartilage and normalization of the growth plate architecture. These findings indicate that VEGF-mediated capillary invasion is an essential signal that regulates growth plate morphogenesis and triggers cartilage remodeling. Thus, VEGF is an essential coordinator of chondrocyte death, chondroclast function, extracellular matrix remodeling, angiogenesis and bone formation in the growth plate.

Lack of reciprocal genomic imprinting of sense and antisense RNA of mouse insulin-like growth factor II receptor in the central nervous system

Two models have been proposed to account for the molecular mechanism underlying genomic imprinting of the insulin-like growth factor II receptor gene (Igf2r): expression-competition and promoter DNA methylation. To examine which model best explains the regulation of Igf2r imprinting, we examined the allelic expression of endogenous Igf2r sense and antisense RNAs in mice. In peripheral tissues, Igf2r sense and antisense RNAs show a reciprocal pattern of imprinting and DNA methylation between the two parental alleles: the sense RNA is monoallelically expressed only from the maternal promoter which is unmethylated in region 1, and the antisense RNA is derived solely from the paternal promoter which is unmethylated in region 2. The paternal promoter of sense Igf2r and the maternal promoter of antisense Igf2r are hypermethylated and are transcriptionally suppressed. In CNS, the genomic imprinting of Igf2r sense and antisense RNAs is uncoupled: both parental promoters of Igf2r gene coding for sense RNA are unmethylated and are biallelically used for transcription. In contrast, antisense RNA of Igf2r is derived only from the paternal allele that is unmethylated in region 2, while the methylated maternal allele is silent. Uncoupling of genomic imprinting of Igf2r sense and antisense RNAs in CNS correlates with DNA methylation of the appropriate promoter region, thus favoring the model of DNA methylation over that of antisense as the chief regulator of Igf2r genomic imprinting.

Kearns-Sayre syndrome: unusual pattern of expression of subunits of the respiratory chain in the cerebellar system

Kearns-Sayre syndrome (KSS) is a sporadic multisystem disorder of oxidative phosphorylation associated with clonally expanded rearrangements of mitochondrial DNA (mtDNA). Mitochondrial dysfunction in the central nervous system of patients with KSS accounts for the neurological manifestations of the disease. To gain further insight into the pathogenesis of neuronal dysfunction in KSS, we used antibodies against mtDNA-encoded and nuclear DNA-encoded subunits of the mitochondrial respiratory chain to study the expression of these proteins in the cerebellar cortex, dentate nucleus, and inferior olivary nucleus from 2 autoptic cases of KSS. Neuropathological examination showed a moderate loss of Purkinje cells and spongiform degeneration of the cerebellar white matter. By using immunohistochemistry, we found a decreased expression of mtDNA-encoded proteins only in neurons of the dentate nucleus. We suggest that mitochondrial abnormalities in the dentate nucleus in conjunction with loss of Purkinje cells and spongiform degeneration of the cerebellar white matter may be important factors in the genesis of the cerebellar dysfunction in KSS.