Human KVLQT1 gene shows tissue-specific imprinting and encompasses Beckwith-Wiedemann syndrome chromosomal rearrangements

The Kcnq1ot1 long non-coding RNA affects chromatin conformation and expression of Kcnq1, but does not regulate its imprinting in the developing heart

Although many of the questions raised by the discovery of imprinting have been answered, we have not yet accounted for tissue- or stage-specific imprinting. The Kcnq1 imprinted domain exhibits complex tissue-specific expression patterns co-existing with a domain-wide cis-acting control element. Transcription of the paternally expressed antisense non-coding RNA Kcnq1ot1 silences some neighboring genes in the embryo, while others are unaffected. Kcnq1 is imprinted in early cardiac development but becomes biallelic after midgestation. To explore this phenomenon and the role of Kcnq1ot1, we used allele-specific assays and chromosome conformational studies in wild-type mice and mice with a premature termination mutation for Kcnq1ot1. We show that Kcnq1 imprinting in early heart is established and maintained independently of Kcnq1ot1 expression, thus excluding a role for Kcnq1ot1 in repressing Kcnq1, even while silencing other genes in the domain. The exact timing of the mono- to biallelic transition is strain-dependent, with the CAST/EiJ allele becoming activated earlier and acquiring higher levels than the C57BL/6J allele. Unexpectedly, Kcnq1ot1 itself also switches to biallelic expression specifically in the heart, suggesting that tissue-specific loss of imprinting may be common during embryogenesis. The maternal Kcnq1ot1 transcript is shorter than the paternal ncRNA, and its activation depends on an alternative transcriptional start site that bypasses the maternally methylated promoter. Production of Kcnq1ot1 on the maternal chromosome does not silence Cdkn1c. We find that in later developmental stages, however, Kcnq1ot1 has a role in modulating Kcnq1 levels, since its absence leads to overexpression of Kcnq1, an event accompanied by an aberrant three-dimensional structure of the chromatin. Thus, our studies reveal regulatory mechanisms within the Kcnq1 imprinted domain that operate exclusively in the heart on Kcnq1, a gene crucial for heart development and function. We also uncover a novel mechanism by which an antisense non-coding RNA affects transcription through regulating chromatin flexibility and access to enhancers.

Effects of perfusion and dynamic loading on human neocartilage formation in alginate hydrogels

Dynamic loading and perfusion culture environments alone are known to enhance cartilage extracellular matrix (ECM) production in dedifferentiated articular chondrocytes. In this study, we explored whether a combination of these factors would enhance these processes over a free-swelling (FS) condition using adult human articular chondrocytes embedded in 2% alginate. The alginate constructs were placed into a bioreactor for perfusion (P) only (100 μL/per minute) or perfusion and dynamic compressive loading (PL) culture (20% for 1 h, at 0.5 Hz), each day. Control FS alginate gels were maintained in six-well static culture. Gene expression analysis was conducted on days 7 and 14, while cell viability, immunostaining, and mechanical property testing were performed on day 14 only. Total glycosaminoglycan (GAG) content and GAG synthesis were assessed after 14 days. Col2a1 mRNA expression levels were significantly higher (at least threefold; p<0.05) in both bioreactor conditions compared with FS by days 7 and 14. For all gene studies, no significant differences were seen between P and PL treatments. Aggrecan mRNA levels were not significantly altered in any condition although both GAG/DNA and (35)S GAG incorporation studies indicated higher GAG retention and synthesis in the FS treatment. Collagen type II protein deposition was low in all samples, link protein distribution was more diffuse in FS condition, and aggrecan deposition was located in the outer regions of the alginate constructs in both bioreactor conditions, yet more uniformly in the FS condition. Catabolic gene expression (matrix metalloproteinase 3 [MMP3] and inducible nitric oxide synthase [iNOS]) was higher in bioreactor conditions compared with FS, although iNOS expression levels decreased to approximately fourfold less than the FS condition by day 14. Our data indicate that conditions created in the bioreactor enhanced both anabolic and catabolic responses, similar to other loading studies. Perfusion was sufficient alone to promote this dual response. PL increased the deposition of aggrecan surrounding cells compared with the other conditions; however, overall low GAG retention in the bioreactor system was likely due to both perfusion and catabolic conditions created. Optimal conditions, which permit appropriate anabolic and catabolic processes for accumulation of ECM and tissue remodeling for neocartilage development, specifically for humans, are needed.

The role of environmental factors in regulating the development of cartilaginous grafts engineered using osteoarthritic human infrapatellar fat pad-derived stem cells

Engineering functional cartilaginous grafts using stem cells isolated from osteoarthritic human tissue is of fundamental importance if autologous tissue engineering strategies are to be used in the treatment of diseased articular cartilage. It has previously been demonstrated that human infrapatellar fat pad (IFP)-derived stem cells undergo chondrogenesis in pellet culture; however, the ability of such cells to generate functional cartilaginous grafts has not been adequately addressed. The objective of this study was to explore how environmental conditions regulate the functional development of cartilaginous constructs engineered using diseased human IFP-derived stem cells (FPSCs). FPSCs were observed to display a diminished chondrogenic potential upon encapsulation in a three-dimensional hydrogel compared with pellet culture, synthesizing significantly lower levels of glycosaminoglycan and collagen on a per cell basis. To engineer more functional cartilaginous grafts, we next explored whether additional biochemical and biophysical stimulations would enhance chondrogenesis within the hydrogels. Serum stimulation was observed to partially recover the diminished chondrogenic potential within hydrogel culture. Over 42 days, stem cells that had first been expanded in a low-oxygen environment proliferated extensively on the outer surface of the hydrogel in response to serum stimulation, assembling a dense type II collagen-positive cartilaginous tissue resembling that formed in pellet culture. The application of hydrostatic pressure did not further enhance extracellular matrix synthesis within the hydrogels, but did appear to alter the spatial accumulation of extracellular matrix leading to the formation of a more compact tissue with superior mechanically functionality. Further work is required in order to recapitulate the environmental conditions present during pellet culture within scaffolds or hydrogels in order to engineer more functional cartilaginous grafts using human osteoarthritic FPSCs.

Inorganic polyphosphate stimulates cartilage tissue formation

Clinical utilization of tissue-engineered cartilage constructs has been limited by their inferior mechanical properties compared to native articular cartilage. A number of strategies have been investigated to increase the accumulation of major extracellular matrix components within in vitro-formed cartilage, including the administration of growth factors and mechanical stimulation. In this study, the anabolic effect of inorganic polyphosphates, a linear polymer of orthophosphate residues linked by phosphoanhydride bonds, was demonstrated in both chondrocyte cultures and native articular cartilage cultured ex vivo. Compared to untreated controls, polyphosphate treatment of three-dimensional primary chondrocyte cultures induced increased glycosaminoglycan and collagen accumulation in a concentration- and chain length-dependent manner. This effect was transient, because chondrocytes express exopolyphosphatases that hydrolyze polyphosphate. The anabolic effect of polyphosphates was accompanied by a lower rate of DNA increase within the chondrocyte cultures treated with inorganic polyphosphate. Inorganic polyphosphate enhances cartilage matrix accumulation and is a promising approach to improve the quality of tissue-engineered cartilage constructs.

Genomic imprinting of the type 3 thyroid hormone deiodinase gene: regulation and developmental implications

BACKGROUND

In recent years, findings in a number of animal and human models have ignited renewed interest in the type 3 deiodinase (D3), the main enzyme responsible for the inactivation of thyroid hormones. The induction of D3 in models of illness and injury has raised critical questions about the physiological significance of reduced thyroid hormone availability in those states. Phenotypes in transgenic mice lacking this enzyme also point to important developmental roles for D3. A critical determinant of D3 expression is genomic imprinting, an epigenetic phenomenon that regulates a small number of dosage-critical genes in the mammalian genome. The D3 gene (Dio3) is imprinted and preferentially expressed from one of the alleles in most tissues.

SCOPE OF REVIEW

In the context of the physiological significance of D3 and the characteristics and purported origins of genomic imprinting, we review the current knowledge about the epigenetic mechanisms specifying gene dosage in the Dio3 locus.

MAJOR CONCLUSIONS

Altered Dio3 dosage is detrimental to development, suggesting that the level of thyroid hormone action needs to be exquisitely tailored in a timely fashion to the requirements of particular tissues. An appropriate Dio3 dosage is the result of the coordinated action of certain genomic elements and epigenetic marks in the Dlk1-Dio3 domain.

GENERAL SIGNIFICANCE

The imprinting of Dio3 prompts intriguing questions about why the level of thyroid hormone signaling should be regulated in this rare epigenetic manner, and to what extent altered Dio3 expression due to aberrant imprinting may be implicated in human conditions. This article is part of a Special Issue entitled Thyroid hormone signalling.

Channeling dysglycemia: ion-channel variations perturbing glucose homeostasis

Maintaining blood glucose homeostasis is a complex process that depends on pancreatic islet hormone secretion. Hormone secretion from islets is coupled to calcium entry which results from regenerative islet cell electrical activity. Therefore, the ionic mechanisms that regulate calcium entry into islet cells are crucial for maintaining normal glucose homeostasis. Genome-wide association studies (GWAS) have identified single-nucleotide polymorphisms (SNPs), including five located in or near ion-channel or associated subunit genes, which show an association with human diseases characterized by dysglycemia. This review focuses on polymorphisms and mutations in ion-channel genes that are associated with perturbations in human glucose homeostasis and discusses their potential roles in modulating pancreatic islet hormone secretion.

Variants in the 3' untranslated region of the KCNQ1-encoded Kv7.1 potassium channel modify disease severity in patients with type 1 long QT syndrome in an allele-specific manner

Aims

Heterozygous mutations in KCNQ1 cause type 1 long QT syndrome (LQT1), a disease characterized by prolonged heart rate-corrected QT interval (QTc) and life-threatening arrhythmias. It is unknown why disease penetrance and expressivity is so variable between individuals hosting identical mutations. We aimed to study whether this can be explained by single nucleotide polymorphisms (SNPs) in KCNQ1's 3′ untranslated region (3′UTR).

Methods and results

This study was performed in 84 LQT1 patients from the Academic Medical Center in Amsterdam and validated in 84 LQT1 patients from the Mayo Clinic in Rochester. All patients were genotyped for SNPs in KCNQ1's 3′UTR, and six SNPs were found. Single nucleotide polymorphisms rs2519184, rs8234, and rs10798 were associated in an allele-specific manner with QTc and symptom occurrence. Patients with the derived SNP variants on their mutated KCNQ1 allele had shorter QTc and fewer symptoms, while the opposite was also true: patients with the derived SNP variants on their normal KCNQ1 allele had significantly longer QTc and more symptoms. Luciferase reporter assays showed that the expression of KCNQ1's 3′UTR with the derived SNP variants was lower than the expression of the 3′UTR with the ancestral SNP variants.

Conclusion

Our data indicate that 3′UTR SNPs potently modify disease severity in LQT1. The allele-specific effects of the SNPs on disease severity and gene expression strongly suggest that they are functional variants that directly alter the expression of the allele on which they reside, and thereby influence the balance between proteins stemming from either the normal or the mutant KCNQ1 allele.

Maternal gametic transmission of translocations or inversions of human chromosome 11p15.5 results in regional DNA hypermethylation and downregulation of CDKN1C expression

Beckwith-Wiedemann syndrome (BWS) is an overgrowth syndrome associated with genetic or epigenetic alterations in one of two imprinted domains on chromosome 11p15.5. Rarely, chromosomal translocations or inversions of chromosome 11p15.5 are associated with BWS but the molecular pathophysiology in such cases is not understood. In our series of 3 translocation and 2 inversion patients with BWS, the chromosome 11p15.5 breakpoints map within the centromeric imprinted domain, 2. We hypothesized that either microdeletions/microduplications adjacent to the breakpoints could disrupt genomic sequences important for imprinted gene regulation. An alternate hypothesis was that epigenetic alterations of as yet unknown regulatory DNA sequences, result in the BWS phenotype. A high resolution Nimblegen custom microarray was designed representing all non-repetitive sequences in the telomeric 33 Mb of the short arm of human chromosome 11. For the BWS-associated chromosome 11p15.5 translocations and inversions, we found no evidence of microdeletions/microduplications. DNA methylation was also tested on this microarray using the HpaII tiny fragment enrichment by ligation-mediated PCR (HELP) assay. This high-resolution DNA methylation microarray analysis revealed a gain of DNA methylation in the translocation/inversion patients affecting the p-ter segment of chromosome 11p15, including both imprinted domains. BWS patients that inherited a maternal translocation or inversion also demonstrated reduced expression of the growth suppressing imprinted gene, CDKN1C in Domain 2. In summary, our data demonstrate that translocations and inversions involving imprinted domain 2 on chromosome 11p15.5, alter regional DNA methylation patterns and imprinted gene expression in cis, suggesting that these epigenetic alterations are generated by an alteration in "chromatin context".

New insights into the pathogenesis of Beckwith-Wiedemann and Silver-Russell syndromes: contribution of small copy number variations to 11p15 imprinting defects

The imprinted 11p15 region is organized in two domains, each of them under the control of its own imprinting control region (ICR1 for the IGF2/H19 domain and ICR2 for the KCNQ1OT1/CDKN1C domain). Disruption of 11p15 imprinting results in two fetal growth disorders with opposite phenotypes: the Beckwith-Wiedemann (BWS) and the Silver-Russell (SRS) syndromes. Various 11p15 genetic and epigenetic defects have been demonstrated in BWS and SRS. Among them, isolated DNA methylation defects account for approximately 60% of patients. To investigate whether cryptic copy number variations (CNVs) involving only part of one of the two imprinted domains account for 11p15 isolated DNA methylation defects, we designed a single nucleotide polymorphism array covering the whole 11p15 imprinted region and genotyped 185 SRS or BWS cases with loss or gain of DNA methylation at either ICR1 or ICR2. We describe herein novel small gain and loss CNVs in six BWS or SRS patients, including maternally inherited cis-duplications involving only part of one of the two imprinted domains. We also show that ICR2 deletions do not account for BWS with ICR2 loss of methylation and that uniparental isodisomy involving only one of the two imprinted domains is not a mechanism for SRS or BWS.

Genomic imprinting: the emergence of an epigenetic paradigm

The emerging awareness of the contribution of epigenetic processes to genome function in health and disease is underpinned by decades of research in model systems. In particular, many principles of the epigenetic control of genome function have been uncovered by studies of genomic imprinting. The phenomenon of genomic imprinting, which results in some genes being expressed in a parental--origin-specific manner, is essential for normal mammalian growth and development and exemplifies the regulatory influences of DNA methylation, chromatin structure and non-coding RNA. Setting seminal discoveries in this field alongside recent progress and remaining questions shows how the study of imprinting continues to enhance our understanding of the epigenetic control of genome function in other contexts.

Hydrogels for the repair of articular cartilage defects

The repair of articular cartilage defects remains a significant challenge in orthopedic medicine. Hydrogels, three-dimensional polymer networks swollen in water, offer a unique opportunity to generate a functional cartilage substitute. Hydrogels can exhibit similar mechanical, swelling, and lubricating behavior to articular cartilage, and promote the chondrogenic phenotype by encapsulated cells. Hydrogels have been prepared from naturally derived and synthetic polymers, as cell-free implants and as tissue engineering scaffolds, and with controlled degradation profiles and release of stimulatory growth factors. Using hydrogels, cartilage tissue has been engineered in vitro that has similar mechanical properties to native cartilage. This review summarizes the advancements that have been made in determining the potential of hydrogels to replace damaged cartilage or support new tissue formation as a function of specific design parameters, such as the type of polymer, degradation profile, mechanical properties and loading regimen, source of cells, cell-seeding density, controlled release of growth factors, and strategies to cause integration with surrounding tissue. Some key challenges for clinical translation remain, including limited information on the mechanical properties of hydrogel implants or engineered tissue that are necessary to restore joint function, and the lack of emphasis on the ability of an implant to integrate in a stable way with the surrounding tissue. Future studies should address the factors that affect these issues, while using clinically relevant cell sources and rigorous models of repair.

The role of imprinted genes in fetal growth abnormalities

Epigenetics, and in particular imprinted genes, have a critical role in the development and function of the placenta, which in turn has a central role in the regulation of fetal growth and development. A unique characteristic of imprinted genes is their expression from only one allele, maternal or paternal and dependent on parent of origin. This unique expression pattern may have arisen as a mechanism to control the flow of nutrients from the mother to the fetus, with maternally expressed imprinted genes reducing the flow of resources and paternally expressed genes increasing resources to the fetus. As a result, any epigenetic deregulation affecting this balance can result in fetal growth abnormalities. Imprinting-associated disorders in humans, such as Beckwith-Wiedemann and Angelman syndrome, support the role of imprinted genes in fetal growth. Similarly, assisted reproductive technologies in animals have been shown to affect the epigenome of the early embryo and the expression of imprinted genes. Their role in disorders such as intrauterine growth restriction appears to be more complex, in that imprinted gene expression can be seen as both causative and protective of fetal growth restriction. This protective or compensatory effect needs to be explored more fully.

High amplitude direct compressive strain enhances mechanical properties of scaffold-free tissue-engineered cartilage

Adult cartilage has a limited healing capacity. Damages resulting from disease or injury increase over time and cause severe pain. One approach to reinstate the cartilage function is tissue engineering (TE). However, the generation of TE cartilage is time consuming and expensive and its properties are so far suboptimal. As in vivo cartilage is subject to loading, it is assumed that mechanical stimulation may enhance the quality of TE cartilage. In this study the short-term influence of variable compressive strain amplitudes on mechanical and biochemical properties of scaffold-free TE cartilage was investigated. Primary porcine chondrocytes were isolated, proliferated, redifferentiated, and transferred onto hydroxyapatite carriers, resulting in scaffold-free cartilage-carrier constructs. These constructs were placed in a custom-made bioreactor. Compression amplitudes of 5%, 10%, and 20% were applied. In each experiment four constructs were loaded with dynamic compression (3000 cycles/day, 1 Hz) for 14 days and four constructs served as unloaded control. The cartilage was evaluated biochemically, histological, and mechanically. No difference in glycosaminoglycan or collagen content between the loaded and the control groups was found. However, a positive correlation between compression amplitude and normalized Young's modulus was detected (R(2)=0.59, p<0.001). The highest compression amplitude of 20% had the strongest positive effect on the mechanical properties of the TE cartilage (Young's modulus increase of 241±28% compared to unloaded control). The data presented suggest that preconditioning with higher load amplitudes might be an attractive way of generating stiffer tissue and may help accelerating the cultivation of mechanically competent TE cartilage.

Heritability of early repolarization: a population-based study

BACKGROUND

Early repolarization (ER), defined by J-point elevation in 12-lead ECG, was recently associated with increased risk for idiopathic ventricular fibrillation and cardiovascular mortality. The determinants of ER are unknown. We investigated its heritability in a large, family-based cohort.

METHODS AND RESULTS

The study sample comprised 1877 individuals from 505 white nuclear families representative of the British general population. Standard 12-lead ECGs were evaluated for the presence of ER, defined as J-point elevation of ≥0.1 mV in at least 2 adjacent inferior (II, III, and aVF) or anterolateral (I, aVL, and V(4) through V(6)) leads. Narrow sense heritability estimates were computed adjusting for age, age(2), and sex. The prevalence of ER was 7.7% (n=145) in the whole cohort, 5.9% (n=56) in parents, and 9.6% (n=89) in offspring. Heritability estimate for the presence of ER was calculated at h(2)=0.49 (standard error=0.14; P=2.7*10(-4)) and was higher when restricted to its presence in inferior leads (h(2)=0.61, standard error=0.18, P=4.3*10(-4)) or for the notching ER morphology (h(2)=0.81, standard error=0.19, P=2.4*10(-5)). Individuals with at least 1 affected parent had a 2.5-fold increased risk for presenting with ER on ECG (odds ratio, 2.54; 95% confidence interval, 1.33 to 4.84; P=0.005). Familial transmission was more frequent when the mother was affected (odds ratio, 3.84; 95% confidence interval, 1.41 to 10.43; P=0.008) than when the father was affected (odds ratio, 1.82; 95% confidence interval, 0.82 to 4.03; P=0.141), although this difference was not statistically significant (P=0.18).

CONCLUSIONS

ER is a heritable phenotype. Offspring of ER-positive parents have a 2.5-fold increased risk of presenting with ER on their ECG.

Beckwith-Wiedemann syndrome

Beckwith-Wiedemann syndrome (BWS) is an imprinting disorder characterized by overgrowth, tumor predisposition, and congenital malformations. Approximately 85% of reported BWS cases are sporadic, while the remaining 15% are familial. BWS is caused by epigenetic or genomic alterations which disrupt genes in one or both of the two imprinted domains on chromosome 11p15.5. In each domain, an imprinting center regulates the expression of imprinted genes in cis. Normally in domain 1, insulin-like growth factor 2 (IGF2) and the untranslated mRNA H19 are monoallelically expressed. In BWS, increased expression of IGF2 occurs via several mechanisms. In domain 2, CDKN1C, a growth repressor, and an untranslated RNA, KCNQ1OT1, are normally expressed monoallelically. In cases of BWS, several mechanisms result in reduced expression of CDKN1C. Recent reports of BWS cases have identified mutations outside the chromosome 11p15.5 critical region, thereby broadening the challenges in the diagnosis and genetic counseling of individuals and families with BWS.

Focal congenital hyperinsulinism in a patient with septo-optic dysplasia

BACKGROUND

An infant diagnosed as having hypopituitarism and on adequate hydrocortisone replacement therapy was referred to a tertiary endocrine unit at 5 weeks of age with persistent hypoglycemia that required a high rate of intravenous glucose infusion (up to 18 mg/kg•min⁻¹) to maintain euglycemia.

INVESTIGATIONS

A controlled hypoglycemia screen was performed to measure levels of plasma glucose, insulin, C-peptide and 3-β-hydroxybutyrate concentrations. The pancreas was analyzed by fluorine-18-L-3,4-dihydroxyphenylalanine ((18)F-DOPA) PET scan. Genetic analyses were performed on the peripheral blood leukocytes, and loss of heterozygosity within the resected focal lesion of the pancreas was investigated by microsatellite analysis. A glucagon stimulation test helped determine pituitary function, and an MRI of the brain and pituitary gland was performed to define the anatomy of the intracranial structures and the pituitary gland.

DIAGNOSIS

Focal form of congenital hyperinsulinism localized to the head of the pancreas, septo-optic dysplasia and pituitary hormone deficiencies.

MANAGEMENT

Resection of the focal lesion from the head of the pancreas and hormonal replacement therapy for hypopituitarism.

Molecular genetics of long QT syndrome

Long QT syndrome (LQTS) is a cardiac disorder associated with sudden death especially in young, seemingly healthy individuals. It is characterised by abnormalities of the heart beat detected as lengthening of the QT interval during cardiac repolarisation. The incidence of LQTS is given as 1 in 2000 but this may be an underestimation as many cases go undiagnosed, due to the rarity of the condition and the wide spectrum of symptoms. Presently 12 genes associated with LQTS have been identified with differing signs and symptoms, depending on the locus involved. The majority of cases have mutations in the KCNQ1 (LQT1), KCNH2 (LQT2) and SCN5A (LQT3) genes. Genetic testing is increasingly used when a clearly affected proband has been identified, to determine the nature of the mutation in that family. Unfortunately tests on probands may be uninformative, especially if the defect does not lie in the set of genes which are routinely tested. Novel mutations in these known LQTS genes and additional candidate genes are still being discovered. The functional implications of these novel mutations need to be assessed before they can be accepted as being responsible for LQTS. Known epigenetic modification affecting KCNQ1 gene expression may also be involved in phenotypic variability of LQTS. Genetic diagnosis of LQTS is thus challenging. However, where a disease associated mutation is identified, molecular diagnosis can be important in guiding therapy, in family testing and in determining the cause of sudden cardiac death. New developments in technology and understanding offer increasing hope to families with this condition.

A genomic imprinting defect in mice traced to a single gene

Mammalian androgenones have two paternally or sperm-derived genomes. In mice (Mus musculus) they die at peri-implantation due to the misexpression of imprinted genes-the genes that are expressed monoallelically according to the parent of origin. The misexpressions involved are poorly defined. To gain further insight, we examined the causes of midgestation death of embryos with paternal duplication (PatDp) of distal chromosome 7 (dist7), a region replete with imprinted genes. PatDp(dist7) embryos have a similar phenotype to mice with a knockout of a maternally expressed imprinted gene, Ascl2 [achaete-scute complex homolog-like 2 (Drosophila)], and their death at midgestation could result from two inactive paternal copies of this gene. However, other dist7 misexpressions could duplicate this phenotype, and the potential epistatic load is undefined. We show that an Ascl2 transgene is able to promote the development of PatDp(dist7) embryos to term, providing strong evidence that Ascl2 is the only imprinted gene in the genome for which PatDp results in early embryonic death. While some of the defects in perinatal transgenic PatDp(dist7) fetuses were consistent with known misexpressions of dist7 imprinted genes, the overall phenotype indicates a role for additional undefined misexpressions of imprinted genes. This study provides implications for the human imprinting-related fetal overgrowth disorder, Beckwith-Wiedemann syndrome.

The importance of imprinting in the human placenta

As a field of study, genomic imprinting has grown rapidly in the last 20 years, with a growing figure of around 100 imprinted genes known in the mouse and approximately 50 in the human. The imprinted expression of genes may be transient and highly tissue-specific, and there are potentially hundreds of other, as yet undiscovered, imprinted transcripts. The placenta is notable amongst mammalian organs for its high and prolific expression of imprinted genes. This review discusses the development of the human placenta and focuses on the function of imprinting in this organ. Imprinting is potentially a mechanism to balance parental resource allocation and it plays an important role in growth. The placenta, as the interface between mother and fetus, is central to prenatal growth control. The expression of genes subject to parental allelic expression bias has, over the years, been shown to be essential for the normal development and physiology of the placenta. In this review we also discuss the significance of genes that lack conservation of imprinting between mice and humans, genes whose imprinted expression is often placental-specific. Finally, we illustrate the importance of imprinting in the postnatal human in terms of several human imprinting disorders, with consideration of the brain as a key organ for imprinted gene expression after birth.

Development of a micromanipulator-based loading device for mechanoregulation study of human mesenchymal stem cells in three-dimensional collagen constructs

Mechanical signal is important for regulating cellular activities, including proliferation, metabolism, matrix production, and orientation. Bioreactors with loading functions can be used to precondition cells in three-dimensional (3D) constructs so as to study the cellular responses to mechanical stimulation. However, full-scale bioreactor is not always an affordable option considering the high cost of equipment and the liter-sized medium with serum and growth factor supplements. In this study, a custom-built loading system was developed by coupling a conventional camera-equipped inverted research microscope with two micromanipulators. The system was programmed to deliver either cyclic compressive loading with different frequencies or static compressive loading for 1 week to investigate the cellular responses of human mesenchymal stem cells (hMSCs) entrapped in a 3D construct consists of reconstituted collagen fibers. Cellular properties, including their alignment, cytoskeleton, and cell metabolism, and properties of matrix molecules, such as collagen fiber alignment and glycosaminoglycan deposition, were evaluated. Using a MatLab-based image analysis program, reorientation of the entrapped cells from a random distribution to a preferred alignment along the loading direction in constructs with both static and cyclic compression has been demonstrated, but no such alignment was found in the free-floating controls. Fluorescent staining on filamentous actin cytoskeleton also confirmed the finding. Nevertheless, the collagen fiber meshwork entrapping the hMSCs remained randomly distributed, and no change in cellular metabolism and glycosaminoglycans production was noted. The current study provides a simple and affordable option toward setting up a mechanoregulation facility based on existing laboratory equipment and sheds new insights on the effect of mechanical loading on the alignment of hMSCs in 3D collagen constructs.

Passaged adult chondrocytes can form engineered cartilage with functional mechanical properties: a canine model

It was hypothesized that previously optimized serum-free culture conditions for juvenile bovine chondrocytes could be adapted to generate engineered cartilage with physiologic mechanical properties in a preclinical, adult canine model. Primary or passaged (using growth factors) adult chondrocytes from three adult dogs were encapsulated in agarose, and cultured in serum-free media with transforming growth factor-beta3. After 28 days in culture, engineered cartilage formed by primary chondrocytes exhibited only small increases in glycosaminoglycan content. However, all passaged chondrocytes on day 28 elaborated a cartilage matrix with compressive properties and glycosaminoglycan content in the range of native adult canine cartilage values. A preliminary biocompatibility study utilizing chondral and osteochondral constructs showed no gross or histological signs of rejection, with all implanted constructs showing excellent integration with surrounding cartilage and subchondral bone. This study demonstrates that adult canine chondrocytes can form a mechanically functional, biocompatible engineered cartilage tissue under optimized culture conditions. The encouraging findings of this work highlight the potential for tissue engineering strategies using adult chondrocytes in the clinical treatment of cartilage defects.

Medium osmolarity and pericellular matrix development improves chondrocyte survival when photoencapsulated in poly(ethylene glycol) hydrogels at low densities

The ability to encapsulate cells over a range of cell densities is important toward mimicking cell densities of native tissues and rationally designing strategies where cell source and/or cell numbers are clinically limited. Our preliminary findings demonstrate that survival of freshly isolated adult bovine chondrocytes dramatically decreases when photoencapsulated in poly(ethylene glycol) hydrogels at low densities (4 million cells/mL). During enzymatic digestion of cartilage, chondrocytes undergo a harsh change in their microenvironment. We hypothesize that the absence of exogenous antioxidants, the hyposmotic environment, and the loss of a protective pericellular matrix (PCM) increase chondrocytes' susceptibility to free radical damage during photoencapsulation. Incorporation of antioxidants and serum into the encapsulation medium improved cell survival twofold compared to phosphate-buffered saline. Increasing medium osmolarity from 330 to 400 mOsm (physiological) improved cell survival by 40% and resulted in approximately 2-fold increase in adenosine triphosphate (ATP) production 24 h postencapsulation. However, cell survival was only temporary. Allowing cells to reproduce some PCM before photoencapsulation in 400 mOsm medium resulted in superior cell survival during and postencapsulation for up to 15 days. In summary, the combination of antioxidants, physiological osmolarity, and the development of some PCM result in an improved robustness against free radical damage during photoencapsulation.

Hyperinsulinism and diabetes: genetic dissection of beta cell metabolism-excitation coupling in mice

The role of metabolism-excitation coupling in insulin secretion has long been apparent, but in recent years, in parallel with studies of human hyperinsulinism and diabetes, genetic manipulation of proteins involved in glucose transport, metabolism, and excitability in mice has brought the central importance of this pathway into sharp relief. We focus on these animal studies and how they provide important insights into not only metabolic and electrical regulation of insulin secretion, but also downstream consequences of alterations in this pathway and the etiology and treatment of insulin-secretion diseases in humans.

Influence of temporary chondroitinase ABC-induced glycosaminoglycan suppression on maturation of tissue-engineered cartilage

OBJECTIVE

A fundamental challenge of cartilage tissue engineering has been the inability to promote collagen synthesis up to native levels. In contrast, recent protocols have demonstrated that glycosaminoglycans (GAG) can be synthesized to native levels in 4-6 weeks of in vitro culture. We hypothesize that rapid GAG synthesis may be an impediment to collagen synthesis, possibly by altering transport pathways of nutrients or synthesis products. In this study, this hypothesis is tested by inducing enzymatic GAG loss in the early culture period of cartilage tissue constructs, and monitoring collagen content at various time points after cessation of enzymatic treatment.

METHODS

In Study 1, to induce breakdown of proteoglycans, chondroitinase ABC (CABC, 0.002U/mL) was continuously added into the culture media for the initial 4 weeks of culture or for 2 weeks starting on day 14 of culture. In Study 2, multiple transient CABC treatments (0.15U/mL, for 2 days) were applied to the matured tissue-engineered constructs.

RESULTS

Continuous and transient CABC treatments significantly increased the collagen concentration of the constructs, improving their tensile properties. The GAG content of the treated constructs recovered quickly to the pretreatment level after 2-3 weeks.

CONCLUSIONS

This study demonstrates that tissue-engineered cartilage constructs with improved tensile properties can be achieved by temporarily suppressing the GAG content enzymatically.

Epigenetic allele silencing and variable penetrance of malignant hyperthermia susceptibility

BACKGROUND

Tissue-specific monoallelic silencing of the RYR1 gene has been proposed as an explanation for variable penetrance of dominant RYR1 mutations in malignant hyperthermia (MH). We examined the hypothesis that monoallelic silencing could explain the inheritance of an MH discordant phenotype in some instances.

METHODS

We analysed parent-offspring transmission data from MH kindreds to assess whether there was any deviation from the expected autosomal dominant Mendelian inheritance pattern. We also evaluated informative single-nucleotide polymorphism (SNP) genotypes in a cohort of unrelated MH patients using genomic DNA (gDNA, prepared from leucocytes) and coding DNA (cDNA, prepared from skeletal muscle). Finally, we examined the segregation of specific mutations at the gDNA and cDNA level within MH families where positive RYR1 gDNA genotype/normal MH phenotype discordance had been observed.

RESULTS

In 2113 transmissions from affected parents, there was a consistent parent-of-origin effect (P<0.001) with affected fathers having fewer affected daughters (20%, 95% CI 17-22%) than affected sons (25%, 95% CI 23-26%) or unaffected daughters (27%, 95% CI 25-30%). No discrepancies were observed between the RYR1 SNP genotypes recorded at the gDNA and cDNA levels. In 14 MH negative individuals from 11 discordant families, the familial mutation was detected in skeletal muscle cDNA in all cases.

CONCLUSIONS

Epigenetic allele silencing may play a role in the inheritance of MH susceptibility, but this is unlikely to involve silencing of RYR1.

Temporal stability and age-related prevalence of loss of imprinting of the insulin-like growth factor-2 gene

BACKGROUND

Loss of genomic imprinting (LOI) of the insulin-like growth factor-2 gene (IGF2) is an epigenetic change involving abnormal activation of the normally silent maternally inherited allele. LOI of IGF2 gene is found in tumor tissue, normal adjoining mucosa and peripheral blood lymphocytes (PBL) of some patients with colorectal cancer (CRC), suggesting that this alteration precedes and is a risk factor for CRC. However, whether LOI of IGF2 is transitory or remains a permanent epigenetic alteration is unknown.

RESULTS

Four-hundred patients, mean age 60.7 years (range 15-95), 287 (80%) Caucasian were studied. This included 210 (51.4%) patients with no colorectal neoplasia, and 190 (48.6) with colorectal neoplasia. LOI of IGF2 was present in all age strata examined, and no statistically significant association across age strata (p trend > 0.05) was noted. Forty-nine patients had repeat analysis of blood imprinting status at a mean follow up time of 38.2 +/- 12.9 months. All but three patients had the same imprinting status at follow up (94% agreement, kappa 0.79, p < 0.001). Genomic imprinting was stable for patients with and without colorectal neoplasia.

METHODS

Standard RT-PCR assays for imprinting analysis of IGF2 were performed on PBL from ApaI informative individuals recruited at baseline and repeated 1 to 3 years later. Prevalence of LOI of IGF2 was also evaluated according to age strata.

CONCLUSION

LOI of the IGF2 gene in PBL appears to be a stable epigenetic phenomenon in most patients. Furthermore, LOI of IGF2 was not associated with age, suggesting an inherited or congenital epigenetic event. These findings support the concept that LOI of IGF2 may be a useful risk factor for CRC predisposition.

Putative imprinted gene expression in uniparental bovine embryo models

Altered patterns of gene expression and the imprinted status of genes have a profound effect on cell physiology and can markedly alter embryonic and fetal development. Failure to maintain correct imprinting patterns can lead to abnormal growth and behavioural problems, or to early pregnancy loss. Recently, it has been reported that the Igf2R and Grb10 genes are biallelically expressed in sheep blastocysts, but monoallelically expressed at Day 21 of development. The present study investigated the imprinting status of 17 genes in in vivo, parthenogenetic and androgenetic bovine blastocysts in order to determine the prevalence of this unique phenomenon. Specifically, the putatively imprinted genes Ata3, Impact, L3Mbtl, Magel2, Mkrn3, Peg3, Snrpn, Ube3a and Zac1 were investigated for the first time in bovine in vitro fertilised embryos. Ata3 was the only gene not detected. The results of the present study revealed that all genes, except Xist, failed to display monoallelic expression patterns in bovine embryos and support recent results reported for ovine embryos. Collectively, the data suggest that monoallelic expression may not be required for most imprinted genes during preimplantation development, especially in ruminants. The research also suggests that monoallelic expression of genes may develop in a gene- and time-dependent manner.

Differential allelic expression in the human genome: a robust approach to identify genetic and epigenetic cis-acting mechanisms regulating gene expression

The recent development of whole genome association studies has lead to the robust identification of several loci involved in different common human diseases. Interestingly, some of the strongest signals of association observed in these studies arise from non-coding regions located in very large introns or far away from any annotated genes, raising the possibility that these regions are involved in the etiology of the disease through some unidentified regulatory mechanisms. These findings highlight the importance of better understanding the mechanisms leading to inter-individual differences in gene expression in humans. Most of the existing approaches developed to identify common regulatory polymorphisms are based on linkage/association mapping of gene expression to genotypes. However, these methods have some limitations, notably their cost and the requirement of extensive genotyping information from all the individuals studied which limits their applications to a specific cohort or tissue. Here we describe a robust and high-throughput method to directly measure differences in allelic expression for a large number of genes using the Illumina Allele-Specific Expression BeadArray platform and quantitative sequencing of RT-PCR products. We show that this approach allows reliable identification of differences in the relative expression of the two alleles larger than 1.5-fold (i.e., deviations of the allelic ratio larger than 60∶40) and offers several advantages over the mapping of total gene expression, particularly for studying humans or outbred populations. Our analysis of more than 80 individuals for 2,968 SNPs located in 1,380 genes confirms that differential allelic expression is a widespread phenomenon affecting the expression of 20% of human genes and shows that our method successfully captures expression differences resulting from both genetic and epigenetic cis-acting mechanisms.

We describe a new methodology to identify individual differences in the expression of the two copies of one gene. This is achieved by comparing the mRNA level of the two alleles using a heterozygous polymorphism in the transcript as marker. We show that this approach allows an exhaustive survey of cis-acting regulation in the genome; we can identify allelic expression differences due to epigenetic mechanisms of gene regulation (e.g. imprinting or X-inactivation) as well as differences due to the presence of polymorphisms in regulatory elements. The direct comparison of the expression of both alleles nullifies possible trans-acting regulatory effects (that influence equally both alleles) and thus complements the findings from gene expression association studies. Our approach can be easily applied to any cohort of interest for a wide range of studies. It notably allows following up association signals and testing whether a gene sitting on a particular haplotype is over- or under-expressed, or can be used for screening cancer tissues for aberrant gene expression due to newly arisen mutations or alteration of the methylation patterns.

Cohesin mediates transcriptional insulation by CCCTC-binding factor

Cohesin complexes mediate sister-chromatid cohesion in dividing cells but may also contribute to gene regulation in postmitotic cells. How cohesin regulates gene expression is not known. Here we describe cohesin-binding sites in the human genome and show that most of these are associated with the CCCTC-binding factor (CTCF), a zinc-finger protein required for transcriptional insulation. CTCF is dispensable for cohesin loading onto DNA, but is needed to enrich cohesin at specific binding sites. Cohesin enables CTCF to insulate promoters from distant enhancers and controls transcription at the H19/IGF2 (insulin-like growth factor 2) locus. This role of cohesin seems to be independent of its role in cohesion. We propose that cohesin functions as a transcriptional insulator, and speculate that subtle deficiencies in this function contribute to 'cohesinopathies' such as Cornelia de Lange syndrome.

Molecular aspects of the congenital and acquired Long QT Syndrome: clinical implications

The Long QT Syndrome (LQTS) is a complex and multi-factorial disorder that predisposes to life-threatening ventricular arrhythmias. Both hereditary and acquired subforms have been identified over the years. Recently, it has become clear that the interaction of multiple acquired and genetic aetiologic factors (e.g. disease modifiers) play an important role in differentiating genotype into a continuous spectrum of clinical or subclinical phenotypes. The genotype-phenotype correlation thereby remains very unpredictable in asymptomatic patients, raising important concerns for clinical practice and also for drug development. Therefore, this review aims at providing a comprehensive overview on LQTS highlighting the molecular mechanisms of arrhythmogenesis involved in both the hereditary and the acquired subtypes of the disorder. From this perspective this manuscript then focuses on how the genotype translates into phenotype. A logical overview is provided with the multitude of hereditary and acquired factors that are involved and of the complexity of the interactions that ultimately result in the heterogeneous expressivity and the unpredictability of the phenotype. Based on recent basic and clinical data this review further aims at providing an update on the clinical properties and management of LQT patients including diagnostic work-up and therapy.

Epigenetic and phenotypic consequences of a truncation disrupting the imprinted domain on distal mouse chromosome 7

The distal end of mouse chromosome 7 (Chr 7) contains a large cluster of imprinted genes. In this region two cis-acting imprinting centers, IC1 (H19 DMR) and IC2 (KvDMR1), define proximal and distal subdomains, respectively. To assess the functional independence of IC1 in the context of Chr 7, we developed a recombinase-mediated chromosome truncation strategy in embryonic stem cells and generated a terminal deletion allele, DelTel7, with a breakpoint in between the two subdomains. We obtained germ line transmission of the truncated Chr 7 and viable paternal heterozygotes, confirming the absence of developmentally required paternally expressed genes distal of Ins2. Conversely, maternal transmission of DelTel7 causes a midgestational lethality, consistent with loss of maternally expressed genes in the IC2 subdomain. Expression and DNA methylation analyses on DelTel7 heterozygotes demonstrate the independent imprinting of IC1 in absence of the entire IC2 subdomain. The evolutionarily conserved linkage between the subdomains is therefore not required for IC1 imprinting on Chr 7. Importantly, the developmental phenotype of maternal heterozygotes is rescued fully by a paternally inherited deletion of IC2. Thus, all the imprinted genes located in the region and required for normal development are silenced by an IC2-dependent mechanism on the paternal allele.

The Use of Ultrasonication to Aid Recellularization of Acellular Natural Tissue Scaffolds for Use in Anterior Cruciate Ligament Reconstruction

Tissue engineering offers a promising solution to the replacement of anterior cruciate ligament. A decellularized porcine patella tendon scaffold was produced by immersing whole tissues sequentially in hypotonic buffer, 0.1% (w/v) sodium dodecyl sulfate (SDS) in hypotonic buffer, and nuclease solution prior to sterilization with 0.1% (w/v) peracetic acid. Initial studies revealed that primary human tenocytes would attach to, but failed to penetrate into, the decellularized scaffold. A novel use of ultrasonication was therefore developed to allow extrinsic cells to migrate into the acellular scaffold. Various intensities of ultrasonication were tested in order to produce a microscopically more open porous matrix without damaging the overall architecture of the scaffold. Ultrasonication treatment with the intensity of 360 W and a pulse time of 1 s for a total of 1 min was found to be the optimal treatment. This process did not have a significant effect upon the biochemical constituents (collagen, glycosaminoglycans), nor did it denature the collagen. Moreover, the acellular sonicated scaffold retained the essential biomechanical characteristics of the native tissue. Primary human tenocytes penetrated into the center of whole acellular sonicated scaffolds over a 3-week period in static culture. The viability of the cells in the center of the scaffold (depth of circa 2.5 mm) was, however, compromised. To circumvent the problem of nutrient limitation, acellular sonicated scaffolds were split into fascicular scaffolds (500 mum thick). Cells seeded onto the fascicular scaffolds penetrated throughout the scaffold and remained viable after 3 weeks of culture. This study has shown that an acellular biocompatible tendon scaffold can be produced using 0.1% (w/v) SDS and that ultrasonication can provide a novel method to enhance the recellularization of decellularized natural tissues.

Genomic organization and imprinting of the Peg3 domain in bovine

Using multiple mammalian genomic sequences, we have analyzed the evolution and imprinting of several genes located in the Peg3 domain, including Mim1 (approved name, Mimt1), Usp29, Zim3, and Zfp264. A series of comparative analyses shows that the overall genomic structure of this 500-kb imprinted domain has been well maintained throughout mammalian evolution but that several lineage-specific changes have also occurred in each species. In the bovine domain, Usp29 has lost its protein-coding capability, Zim3 has been duplicated, and the expression of Zfp264 has become biallelic in brain and testis, which differs from paternal expression of mouse Zfp264 in brain. In contrast, the two transcript genes of cow, Mim1 and Usp29, both lacking protein-coding capability, are still expressed mainly from the paternal allele, indicating the imprinting of these two genes in cow. The imprinting of Mim1 and Usp29 along with Peg3 is the most evolutionarily selected feature in this imprinted domain, suggesting significant function of these three genes, either as protein-coding or as untranslated transcript genes.

A single hERG mutation underlying a spectrum of acquired and congenital long QT syndrome phenotypes

The long QT syndrome (LQTS) is a multi-factorial disorder that predisposes to life-threatening arrhythmias. Both hereditary and acquired subforms have been identified. Here, we present clinical and biophysical evidence that the hERG mutation c.1039 C>T (p.Pro347Ser or P347S) is responsible for both the acquired and the congenital phenotype. In one case the genotype remained silent for years until the administration of several QT-prolonging drugs resulted into a full-blown phenotype, that was reversible upon cessation of these compounds. On the other hand the mutation was responsible for a symptomatic congenital LQTS in a Dutch family, displaying a substantial heterogeneity of the clinical symptoms. Biophysical characterization of the p.Pro347Ser potassium channels using whole-cell patch clamp experiments revealed a novel pathogenic mechanism of reciprocal changes in the inactivation kinetics combined with a dominant-negative reduction of the functional expression in the heterozygous situation, yielding a modest genetic predisposition for LQTS. Our data show that in the context of the multi-factorial aetiology underlying LQTS a modest reduction of the repolarizing power can give rise to a spectrum of phenotypes originating from one mutation. This observation increases the complexity of genotype-phenotype correlations in more lenient manifestations of the disease and underscores the difficulty of predicting the expressivity of the LQTS especially for mutations with a more subtle impact such as p.Pro347Ser.

Syndromes and Disorders Associated with Omphalocele (I): Beckwith–Wiedemann Syndrome

Beckwith-Wiedemann syndrome (BWS, OMIM 130650) is characterized by macrosomia, macroglossia, visceromegaly, hemihypertrophy, abdominal wall defects, ear creases/pits, neonatal hypoglycemia, polyhydramnios, placentomegaly, placental mesenchymal dysplasia, cardiac defects, nevus flammeus, hemangiomata, and an increased frequency of embryonal tumors. This article provides an overview of BWS including the genetics, genetic diagnosis, genotype/epigenotype-phenotype correlations, association with assisted reproductive technology, and prenatal diagnosis. Omphalocele is an important sonographic marker for BWS. Prenatal detection of omphalocele, fetal overgrowth, polyhydramnios, increased abdominal circumference, placentomegaly and/or placental mesenchymal dysplasia should alert one to the possibility of BWS and prompt a genetic investigation and counseling for BWS.

Paternally Inherited Submicroscopic Duplication at 11p15.5 Implicates Insulin-like Growth Factor II in Overgrowth and Wilms' Tumorigenesis

Loss of imprinting at insulin-like growth factor II (IGFII), in association with H19 silencing, has been described previously in a subgroup of Beckwith-Wiedemann syndrome (BWS) patients who have an elevated risk for Wilms' tumor. An equivalent somatic mutation occurs in sporadic Wilms' tumor. We describe a family with overgrowth in three generations and Wilms' tumor in two generations, with paternal inheritance of a cis-duplication at 11p15.5 spanning the BWS IC1 region and including H19, IGFII, INS, and TH. The duplicated region was below the limit of detection by high-resolution karyotyping and fluorescence in situ hybridization, has a predicted minimum size of 400 kb, and was confirmed by genotyping and gene-dosage analysis on a CytoChip comparative genomic hybridization bacterial artificial chromosome array. IGFII is the only known paternally expressed oncogene mapping within the duplicated region and our findings directly implicate IGFII in Wilms' tumorigenesis and add to the mutation spectrum that increases the effective dose of IGFII. Furthermore, this study raises the possibility that sporadic cases of overgrowth and Wilms' tumor, presenting with apparent gain of methylation at IC1, may be explained by submicroscopic paternal duplications. This finding has important implications for determining the transmission risk in these disorders.

Mechanical Loading-Dependence of mRNA Expressions of Extracellular Matrices of Chondrocytes Inoculated into Elastomeric Microporous Poly(L-lactide-co-ε-caprolactone) Scaffold

The temporal response of young rabbit chondrocyte metabolism (including biosynthesis of extracellular matrix macromolecules such as collagen and aggrecan, both of which are essential components of normal cartilage tissue, and their messenger ribonucleic acid (mRNA) expression) in microporous elastomeric scaffolds made of poly(L-lactide-co-epsilon-caprolactone) subjected to different compressive regimes (loading frequency, loading duration per cycle, loading period, and continuous or intermittent compression) were studied over a 6-day culture period at 10% of compressive strain. A continuous dynamic compression improved the production of sulfated glycosaminoglycan (S-GAG), most of which was released into the culture medium upon loading. High mRNA expression of type II collagen was exhibited at a frequency of 0.1 Hz. Little frequency dependency was observed for aggrecan. An intermittent loading (24-h cycle of loading and unloading) or short loading and unloading duration per cycle-compression regime maintained high levels of mRNA expression. This strongly suggests that well-controlled mechanical conditioning regimes may control the gene expression of key metabolic substances relevant to functional cartilage tissue while the degree of release of these substances into the culture medium is minimized.

Molecular and genomic characterisation of cryptic chromosomal alterations leading to paternal duplication of the 11p15.5 Beckwith-Wiedemann region

BACKGROUND

Beckwith-Wiedemann syndrome (BWS) is an overgrowth disorder with increased risk of paediatric tumours. The aetiology involves epigenetic and genetic alterations affecting the 11p15 region, methylation of the differentially methylated DMR2 region being the most common defect, while less frequent aetiologies include mosaic paternal 11p uniparental disomy (11patUPD), maternally inherited mutations of the CDKN1C gene, and hypermethylation of DMR1. A few patients have cytogenetic abnormalities involving 11p15.5.

METHODS

Screening of 70 trios of BWS probands for 11p mosaic paternal UPD and for cryptic cytogenetic rearrangements using microsatellite segregation analysis identified a profile compatible with paternal 11p15 duplication in two patients.

RESULTS

Fluorescence in situ hybridisation analysis revealed in one case the unbalanced translocation der(21)t(11;21)(p15.4;q22.3) originated from missegregation of a cryptic paternal balanced translocation. The second patient, trisomic for D11S1318, carried a small de novo dup(11)(p15.5p15.5), resulting from unequal recombination at paternal meiosis I. The duplicated region involves only IC1 and spares IC2/LIT1, as shown by fluorescent in situ hybridisation (FISH) mapping of the proximal duplication breakpoint within the amino-terminal part of KvLQT1.

CONCLUSIONS

An additional patient with Wolf-Hirschorn syndrome was shown by FISH studies to carry a der(4)t(4;11)(p16.3;p15.4), contributed by a balanced translocation father. Interestingly, refined breakpoint mapping on 11p and the critical regions on the partner 21q and 4p chromosomal regions suggested that both translocations affecting 11p15.4 are mediated by segmental duplications. These findings of chromosomal rearrangements affecting 11p15.5-15.4 provide a tool to further dissect the genomics of the BWS region and the pathogenesis of this imprinting disorder.

Glucose Concentration and Medium Volume Influence Cell Viability and Glycosaminoglycan Synthesis in Chondrocyte-Seeded Alginate Constructs

Increasing the thickness of tissue-engineered cartilage is associated with loss of chondrocyte viability and biosynthetic activity at the tissue center. Exceptionally high volumes of culture medium, however, can maintain cellularity and glycosaminoglycan synthesis throughout 4-mm-thick constructs. We hypothesized that glucose supplementation could replicate the augmentation of tissue formation achieved by medium volume. Chondrocyte-alginate constructs (40x10(6) cells/mL) were cultured for 14 days in 0.4-6.4 mL/10(-6) cells of either low- (5.1 mM) or high- (20.4 mM) glucose medium. Glucose was critical to chondrocyte viability, and glucose uptake increased significantly (P < .001) with both medium volume and glucose supplementation. After 14 days, constructs cultured in 0.4 mL/10(-6) cells of low-glucose medium had a mass of 172 +/- 6.1 mg and glycosaminoglycan (GAG) content of 0.32 +/- 0.03 mg (mean +/- standard deviation). A 4-fold increase in medium volume increased the final construct mass by 44% and GAG content by 207%. An equivalent increase in glucose supply in the absence of volume change increased these parameters by just 10% and 73%, respectively. A similar trend was observed from 0.8 to 3.2 mL/10(-6) cells, when maximal values of construct GAG content and mass were obtained. Therefore, medium volume remains an important consideration for the optimal culture of tissue-engineered cartilage.

Skipping of Exon 1 in the KCNQ1 Gene Causes Jervell and Lange-Nielsen Syndrome

The Jervell and Lange-Nielsen syndrome (JLNS) is a rare autosomal recessive form of the long QT syndrome linked with a profound hearing loss caused by mutations affecting both alleles of either the KCNQ1 or the KCNE1 gene. We carried out a mutant screening of the KCNQ1 and KCNE1 genes in a clinical diagnosed German family with JLNS. Family members were examined by single strand conformation polymorphism analysis and PCR and amplified products were characterized by DNA sequence analysis. We identified a splice donor mutation of exon 1 in the KCNQ1 gene (G477+1A). Analysis of lymphocyte RNA by RT-PCR revealed that two symptomatic patients, homozygous for the mutant allele, exclusively produce KCNQ1 transcripts lacking exon 1 leading to a frameshift that introduced a premature termination codon at exon 4. Mutant subunits, functionally characterized in Xenpous oocytes, were unable to form homomeric channels but strongly reduced IKs (slowly activating delayed rectifier potassium current) in vitro (mutant isoforms 1 and 2 by 62 and 86%, respectively), a fact supposed to lead to severely affected heterozygous individuals. However, individuals heterozygous for the mutant allele exhibit an asymptomatic cardiac phenotype. Thus, the observed dominant-negative effect of mutant subunits in vitro is absent in vivo leaving heterozygous individuals unaffected. These data suggest mechanisms that prevent production of truncated KCNQ1 channel subunits in cardiomyocytes of individuals heterozygous for the mutant allele.

Epigenetic allele silencing unveils recessive RYR1 mutations in core myopathies

Epigenetic regulation of gene expression is a source of genetic variation, which can mimic recessive mutations by creating transcriptional haploinsufficiency. Germline epimutations and genomic imprinting are typical examples, although their existence can be difficult to reveal. Genomic imprinting can be tissue specific, with biallelic expression in some tissues and monoallelic expression in others or with polymorphic expression in the general population. Mutations in the skeletal-muscle ryanodine-receptor gene (RYR1) are associated with malignant hyperthermia susceptibility and the congenital myopathies central core disease and multiminicore disease. RYR1 has never been thought to be affected by epigenetic regulation. However, during the RYR1-mutation analysis of a cohort of patients with recessive core myopathies, we discovered that 6 (55%) of 11 patients had monoallelic RYR1 transcription in skeletal muscle, despite being heterozygous at the genomic level. In families for which parental DNA was available, segregation studies showed that the nonexpressed allele was maternally inherited. Transcription analysis in patients' fibroblasts and lymphoblastoid cell lines indicated biallelic expression, which suggests tissue-specific silencing. Transcription analysis of normal human fetal tissues showed that RYR1 was monoallelically expressed in skeletal and smooth muscles, brain, and eye in 10% of cases. In contrast, 25 normal adult human skeletal-muscle samples displayed only biallelic expression. Finally, the administration of the DNA methyltransferase inhibitor 5-aza-deoxycytidine to cultured patient skeletal-muscle myoblasts reactivated the transcription of the silenced allele, which suggests hypermethylation as a mechanism for RYR1 silencing. Our data indicate that RYR1 undergoes polymorphic, tissue-specific, and developmentally regulated allele silencing and that this unveils recessive mutations in patients with core myopathies. Furthermore, our data suggest that imprinting is a likely mechanism for this phenomenon and that similar mechanisms could play a role in human phenotypic heterogeneity.

Parentally imprinted allele typing at a short tandem repeat locus in intron 1a of imprinted gene KCNQ1

A short tandem repeat (STR) in the intron 1a of paternally imprinted gene, KCNQ1, is evaluated as a new probe for use in parentally imprinting allele (PIA) typing. This typing can determine the inheritance of one allele from father by the methylation difference. Allelic and genotypic frequencies of the STR were determined using samples from 175 unrelated Japanese and 170 unrelated Germans. The polymorphism information contents were 0.652 and 0.634 for the Japanese and the Germans, respectively, indicating usefulness in individual identification. This method was applied to five Japanese families consisting of 19 individuals. Genomic DNA was digested by methylation-sensitive restriction endonucleases, HhaI and HapII, followed by PCR amplification using two-step sandwich primer sets and the products were analyzed on polyacrylamide gel electrophoresis. For all of the families, each child's paternal allele given by PIA typing corresponded to one of the two alleles from father, not the two from mother, that were determined by the STR genotyping. The results demonstrate that this STR probe is feasible for use in PIA typing and that its typing method can contribute to paternity testing.

Genome-wide survey of imprinted genes

The developmental failure of mammalian parthenogenote has been a mystery for a long time and posed a question as to why bi-parental reproduction is necessary for development to term. In the 1980s, it was proven that this failure was not due to the genetic information itself, but to epigenetic modification of genomic DNA. In the following decade, several studies successfully identified imprinted genes which were differentially expressed in a parent-of-origin-specific manner, and it was shown that the differential expression depended on the pattern of DNA methylation. These facts prompted development of genome-wide systematic screening methods based on DNA methylation and differential gene expression to identify imprinted genes. Recently computational approaches and microarray technology have been introduced to identify imprinted genes/loci, contributing to the expansion of our knowledge. However, it has been shown that the gene silencing derived from genomic imprinting is accomplished by several mechanisms in addition to direct DNA methylation, indicating that novel approaches are further required for comprehensive understanding of genomic imprinting. To unveil the mechanism of developmental failure in mammalian parthenogenote, systematic screenings for imprinted genes/loci have been developed. In this review, we describe genomic imprinting focusing on the history of genome-wide screening.

Localization of Type VI Collagen in Tissue-Engineered Cartilage on Polymer Scaffolds

Together, the chondrocyte and its pericellular matrix have been collectively termed the chondron. Current opinion is that the pericellular matrix has both protective and signalling functions between chondrocyte and extracellular matrix. Formation of a native chondrocyte pericellular matrix or chondron structure might therefore be advantageous when tissue engineering a functional hyaline cartilage construct. The presence of chondrons has not been previously described in cartilage engineered on a scaffold. In this paper, we describe a modified immunochemical method to detect collagen VI, a key molecular marker for the pericellular matrix, and an investigation of type VI collagen distribution in engineered hyaline cartilage constructs. Cartilage constructs were engineered from adult human or bovine hyaline chondrocytes cultured on sponge or nonwoven fiber based HYAFF 11 scaffolds. Type VI collagen was detected in all constructs, but a distinctive, high-density, chondron-like distribution of collagen VI was present only in constructs exhibiting additional features of hyaline cartilage engineered using nonwoven HYAFF 11. Chondron structures were localized in areas of the extracellular matrix displaying strong collagen II and GAG staining of constructs where type II collagen composed a high percentage (over 65%) of the total collagen.

The KCNQ1 potassium channel: from gene to physiological function

The voltage-gated KCNQ1 (KvLQT1, Kv7.1) potassium channel plays a crucial role in shaping the cardiac action potential as well as in controlling the water and salt homeostasis in several epithelial tissues. KCNQ1 channels in these tissues are tightly regulated by auxiliary proteins and accessory factors, capable of modulating the properties of the channel complexes. This paper reviews the current knowledge about the KCNQ1 channel with a major focus on interacting proteins and physiological functions.

L3mbtl, the mouse orthologue of the imprinted L3MBTL, displays a complex pattern of alternative splicing and escapes genomic imprinting

L3mbtl encodes a member of the Polycomb group of proteins, which function as transcriptional repressors in large protein complexes. The Drosophila D-l(3)mbt protein is considered a tumor suppressor since its inactivation results in brain tumors. The human L3MBTL gene lies in a region of chromosome 20 frequently deleted in patients with myeloid malignancies and has been proposed as a candidate 20q tumor suppressor gene. Recently we have shown that L3MBTL undergoes monoallelic methylation in hematopoietic tissues and is transcribed from the paternally derived allele. The mouse L3mbtl gene is located on chromosome 2, a region of syntenic homology with human chromosome 20, and in a region containing a number of genes subject to epigenetic regulation. Here we analyze the genomic structure and alternative splicing of L3mbtl and assess its imprinting status in mouse. L3mbtl displays a complex pattern of alternative splicing involving both 5' noncoding and coding exons and is transcribed from two promoters. Unlike its human counterpart, L3mbtl escapes imprinting and there is no differential methylation of its CpG island.