New p57KIP2 mutations in Beckwith-Wiedemann syndrome

Pivotal functions and impact of long con-coding RNAs on cellular processes and genome integrity

Recent advances in uncovering the mysteries of the human genome suggest that long non-coding RNAs (lncRNAs) are important regulatory components. Although lncRNAs are known to affect gene transcription, their mechanisms and biological implications are still unclear. Experimental research has shown that lncRNA synthesis, subcellular localization, and interactions with macromolecules like DNA, other RNAs, or proteins can all have an impact on gene expression in various biological processes. In this review, we highlight and discuss the major mechanisms through which lncRNAs function as master regulators of the human genome. Specifically, the objective of our review is to examine how lncRNAs regulate different processes like cell division, cell cycle, and immune responses, and unravel their roles in maintaining genomic architecture and integrity.

The various regulatory functions of long noncoding RNAs in apoptosis, cell cycle, and cellular senescence

Long noncoding RNAs (lncRNAs) are a group of noncoding cellular RNAs involved in significant biological phenomena such as differentiation, cell development, genomic imprinting, adjusting the enzymatic activity, regulating chromosome conformation, apoptosis, cell cycle, and cellular senescence. The misregulation of lncRNAs interrupting normal biological processes has been implicated in tumor formation and metastasis, resulting in cancer. Apoptosis and cell cycle, two main biological phenomena, are highly conserved and intimately coupled mechanisms. Hence, some cell cycle regulators can influence both programmed cell death and cell division. Apoptosis eliminates defective and unwanted cells, and the cell cycle enables cells to replicate themselves. The improper regulation of apoptosis and cell cycle contributes to numerous disorders such as neurodegenerative and autoimmune diseases, viral infection, anemia, and mainly cancer. Cellular senescence is a tumor-suppressing response initiated by environmental and internal stress factors. This phenomenon has recently attained more attention due to its therapeutic implications in the field of senotherapy. In this review, the regulatory roles of lncRNAs on apoptosis, cell cycle, and senescence will be discussed. First, the role of lncRNAs in mitochondrial dynamics and apoptosis is addressed. Next, the interaction between lncRNAs and caspases, pro/antiapoptotic proteins, and also EGFR/PI3K/PTEN/AKT/mTORC1 signaling pathway will be investigated. Furthermore, the effect of lncRNAs in the cell cycle is surveyed through interaction with cyclins, cdks, p21, and wnt/β-catenin/c-myc pathway. Finally, the function of essential lncRNAs in cellular senescence is mentioned.

The Rare Association of Cleft Lip and/or Palate and Wilms Tumor

There is currently no recognized connection between the occurrence of cleft lip and/or palate (CL/P) and Wilms tumor (WT). A retrospective review of cleft team records (2001-2015) revealed 3 cases of children, all male, with concomitant diagnoses of CL/P and WT treated at our institution. These patients presented as infants for care of their CL/P, all with additional congenital anomalies, developmental delays, and growth delays. Between the ages of 1 and 4 years, each was diagnosed with WT, which was treated with chemotherapy and partial nephrectomy, +/- radiation, leading to full remission in all cases.

Behavioural abnormalities in a novel mouse model for Silver Russell Syndrome

Silver Russell Syndrome (SRS) syndrome is an imprinting disorder involving low birth weight with complex genetics and diagnostics. Some rare SRS patients carry maternally inherited microduplications spanning the imprinted genes CDKN1C, PHLDA2, SLC22A18 and KCNQ1, suggesting that overexpression of one of more of these genes contributes to the SRS phenotype. While this molecular alteration is very rare, feeding difficulties are a very common feature of this condition. Given that SRS children also have very low body mass index, understanding the underpinning biology of the eating disorder is important, as well as potential co-occurring behavioural alterations. Here, we report that a mouse model of this microduplication exhibits a number of behavioural deficits. The mice had a blunted perception of the palatability of a given foodstuff. This perception may underpin the fussiness with food. We additionally report hypoactivity, unrelated to anxiety or motoric function, and a deficit in the appropriate integration of incoming sensory information. Importantly, using a second genetic model, we were able to attribute all altered behaviours to elevated expression of a single gene, Cdkn1c. This is the first report linking elevated Cdkn1c to altered behaviour in mice. Importantly, the findings from our study may have relevance for SRS and highlight a potentially underreported aspect of this disorder.

Clinical and molecular analyses of Beckwith-Wiedemann syndrome: Comparison between spontaneous conception and assisted reproduction techniques

Beckwith-Wiedemann syndrome (BWS) is an overgrowth syndrome characterized by an excessive prenatal and postnatal growth, macrosomia, macroglossia, and hemihyperplasia. The molecular basis of this syndrome is complex and heterogeneous, involving genes located at 11p15.5. BWS is correlated with assisted reproductive techniques. BWS in individuals born following assisted reproductive techniques has been found to occur four to nine times higher compared to children with to BWS born after spontaneous conception. Here, we report a series of 187 patients with to BWS born either after assisted reproductive techniques or conceived naturally. Eighty-eight percent of BWS patients born via assisted reproductive techniques had hypomethylation of KCNQ1OT1:TSS-DMR in comparison with 49% for patients with BWS conceived naturally. None of the patients with BWS born via assisted reproductive techniques had hypermethylation of H19/IGF2:IG-DMR, neither CDKN1 C mutations nor patUPD11. We did not find differences in the frequency of multi-locus imprinting disturbances between groups. Patients with BWS born via assisted reproductive techniques had an increased frequency of advanced bone age, congenital heart disease, and decreased frequency of earlobe anomalies but these differences may be explained by the different molecular background compared to those with BWS and spontaneous fertilization. We conclude there is a correlation of the molecular etiology of BWS with the type of conception. © 2016 Wiley Periodicals, Inc.

p57(Kip2) knock-in mouse reveals CDK-independent contribution in the development of Beckwith-Wiedemann syndrome

CDKN1C encodes the cyclin-CDK inhibitor p57(Kip2) (p57), a negative regulator of the cell cycle and putative tumour suppressor. Genetic and epigenetic alterations causing loss of p57 function are the most frequent cause of Beckwith-Wiedemann syndrome (BWS), a genetic disorder characterized by multiple developmental anomalies and increased susceptibility to tumour development during childhood. So far, BWS development has been attributed entirely to the deregulation of proliferation caused by loss of p57-mediated CDK inhibition. However, a fraction of BWS patients have point mutations in CDKN1C located outside of the CDK inhibitory region, suggesting the involvement of other parts of the protein in the disease. To test this possibility, we generated knock-in mice deficient for p57-mediated cyclin-CDK inhibition (p57(CK) (-) ), the only clearly defined function of p57. Comparative analysis of p57(CK) (-) and p57(KO) mice provided clear evidence for CDK-independent roles of p57 and revealed that BWS is not caused entirely by CDK deregulation, as several features of BWS are caused by the loss of CDK-independent roles of p57. Thus, while the genetic origin of BWS is well understood, our results underscore that the underlying molecular mechanisms remain largely unclear. To probe these mechanisms further, we determined the p57 interactome. Several partners identified are involved in genetic disorders with features resembling those caused by CDKN1C mutation, suggesting that they could be involved in BWS pathogenesis and revealing a possible connection between seemingly distinct syndromes. Copyright © 2016 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Diagnosis and Management of Hereditary Adrenal Cancer

Benign adrenocortical tumours (ACT) are relatively frequent lesions; on the contrary, adrenocortical carcinoma (ACC) is a rare and aggressive malignancy with unfavourable prognosis. Recent advances in the molecular understanding of adrenal cancer offer promise for better therapies in the future. Many of these advances stem from the molecular elucidation of genetic conditions predisposing to the development of ACC. Six main clinical syndromes have been described to be associated with hereditary adrenal cancer. In these conditions, genetic counselling plays an important role for the early detection and follow-up of the patients and the affected family members.

Recommendations of the Scientific Committee of the Italian Beckwith-Wiedemann Syndrome Association on the diagnosis, management and follow-up of the syndrome

Beckwith-Wiedemann syndrome (BWS) is the most common (epi)genetic overgrowth-cancer predisposition disorder. Given the absence of consensual recommendations or international guidelines, the Scientific Committee of the Italian BWS Association (www.aibws.org) proposed these recommendations for the diagnosis, molecular testing, clinical management, follow-up and tumor surveillance of patients with BWS. The recommendations are intended to allow a timely and appropriate diagnosis of the disorder, to assist patients and their families, to provide clinicians and caregivers optimal strategies for an adequate and satisfactory care, aiming also at standardizing clinical practice as a national uniform approach. They also highlight the direction of future research studies in this setting. With recent advances in understanding the disease (epi)genetic mechanisms and in describing large cohorts of BWS patients, the natural history of the disease will be dissected. In the era of personalized medicine, the emergence of specific (epi)genotype-phenotype correlations in BWS will likely lead to differentiated follow-up approaches for the molecular subgroups, to the development of novel tools to evaluate the likelihood of cancer development and to the refinement and optimization of current tumor screening strategies.

CONCLUSIONS

In this article, we provide the first comprehensive recommendations on the complex management of patients with Beckwith-Wiedemann syndrome.

Tumor Suppressor Inactivation in the Pathogenesis of Adult T-Cell Leukemia

Tumor suppressor functions are essential to control cellular proliferation, to activate the apoptosis or senescence pathway to eliminate unwanted cells, to link DNA damage signals to cell cycle arrest checkpoints, to activate appropriate DNA repair pathways, and to prevent the loss of adhesion to inhibit initiation of metastases. Therefore, tumor suppressor genes are indispensable to maintaining genetic and genomic integrity. Consequently, inactivation of tumor suppressors by somatic mutations or epigenetic mechanisms is frequently associated with tumor initiation and development. In contrast, reactivation of tumor suppressor functions can effectively reverse the transformed phenotype and lead to cell cycle arrest or death of cancerous cells and be used as a therapeutic strategy. Adult T-cell leukemia/lymphoma (ATLL) is an aggressive lymphoproliferative disease associated with infection of CD4 T cells by the Human T-cell Leukemia Virus Type 1 (HTLV-I). HTLV-I-associated T-cell transformation is the result of a multistep oncogenic process in which the virus initially induces chronic T-cell proliferation and alters cellular pathways resulting in the accumulation of genetic defects and the deregulated growth of virally infected cells. This review will focus on the current knowledge of the genetic and epigenetic mechanisms regulating the inactivation of tumor suppressors in the pathogenesis of HTLV-I.

Novel fetal and maternal sonographic findings in confirmed cases of Beckwith-Wiedemann syndrome

OBJECTIVE

The objective of the study was to examine the prenatal anomalies in fetuses with Beckwith-Wiedemann syndrome (BWS).

METHODS

The study included a retrospective assessment of 12 pregnancies that were seen at three tertiary referral centres (Universities of Tübingen, Bonn, and Cologne/Germany). The genetic mutation, the results of the second trimester ultrasound examination, and the outcome of the pregnancies are shown. Biometric data were transformed into z-values.

RESULTS

Median gestational age at the time of examination was 22.6 (range 19.0-29.7) weeks of gestation. In all cases, the head circumference (HC) and the femur length (FL) were within the normal range, but the HC-FL ratio was above the 95th centile in 75% of the cases. An exomphalos, macroglossia, and visceromegaly were observed in 67%, 50%, and 83% of the cases, and in 58% and 83%, there were polyhydramnios and placentamegaly respectively. The fetal pancreas was identified in three quarters of the cases. A third of the women had large, overstimulation-like ovaries, although each pregnancy was conceived naturally. In four cases, beta-human chorionic gonadotropin (hCG) levels were measured and mean hCG levels were 498 106 IU/L.

DISCUSSION

Besides exomphalos, BWS should be considered if there is macroglossia, a distinct growth pattern, pancreatic hyperplasia, placentamegaly, and substantially increased levels of beta-hCG. © 2015 John Wiley & Sons, Ltd.

CDKN1C mutation affecting the PCNA-binding domain as a cause of familial Russell Silver syndrome

BACKGROUND

Russell Silver syndrome (RSS) leads to prenatal and postnatal growth retardation. About 55% of RSS patients present a loss-of-methylation of the paternal ICR1 domain on chromosome 11p15. CDKN1C is a cell proliferation inhibitor encoded by an imprinted gene in the 11p15 ICR2 domain. CDKN1C mutations lead to Beckwith Wiedemann syndrome (BWS, overgrowth syndrome) and in IMAGe syndrome which associates growth retardation and adrenal insufficiency. We searched for CDKN1C mutations in a cohort of clinically diagnosed RSS patients with no molecular anomaly.

METHOD

The coding sequence and intron-exon boundaries of CDKN1C were analysed in 97 RSS patients. The impact of CDKN1C variants on the cell cycle in vitro were determined by flow cytometry. Stability of CDKN1C was studied by western immunoblotting after inhibition of translation with cycloheximide.

RESULTS

We identified the novel c.836G>[G;T] (p.Arg279Leu) mutation in a familial case of intrauterine growth retardation (IUGR) with RSS phenotype and no evidence of IMAGe. All the RSS patients inherited this mutation from their mothers (consistent with monoallelic expression from the maternal allele of the gene). A mutation of this amino acid (p.Arg279Pro) has been reported in cases of IMAGe. Functional analysis showed that Arg279Leu (RSS) did not affect the cell cycle, whereas the Arg279Pro mutation (IMAGe) led to a gain of function. Arg279Leu (RSS) led to an increased stability which could explain an increased activity of CDKN1C.

CONCLUSIONS

CDKN1C mutations cause dominant maternally transmitted RSS, completing the molecular mirror with BWS. CDKN1C should be investigated in cases with family history of RSS.

Molecular findings in Beckwith-Wiedemann syndrome

Our understanding of Beckwith-Wiedemann syndrome (BWS) has recently been enhanced by advances in its molecular characterization. These advances have further delineated intricate (epi)genetic regulation of the imprinted gene cluster on chromosome 11p15.5 and the role of these genes in normal growth and development. Studies of the molecular changes associated with the BWS phenotype have been instrumental in elucidating critical molecular elements in this imprinted region. This review will provide updated information on the multiple new regulatory elements that have been recently found to contribute to in cis or in trans control of imprinted gene expression in the chromosome 11p15.5 region and the clinical expression of the BWS phenotype.

CDK inhibitor p57 (Kip2) is downregulated by Akt during HER2-mediated tumorigenicity

HER2/neu oncogene is frequently deregulated in cancers, and the (PI3K)-Akt signaling is one of the major pathways in mediating HER2/neu oncogenic signal. p57 (Kip2) , an inhibitor of cyclin-depependent kinases, is pivotal in regulating cell cycle progression, but its upstream regulators remain unclear. Here we show that the HER2-Akt axis is linked to p57 (Kip2) regulation, and that Akt is a negative regulator of p57 (Kip2) . Ectopic expression of Akt can decrease the expression of p57 (Kip2) , while Akt inhibition leads to p57 (Kip2) stabilization. Mechanistic studies show that Akt interacts with p57 (Kip2) and causes cytoplasmic localization of p57 (Kip2) . Akt phosphorylates p57 on Ser 282 or Thr310. Akt activity results in destabilization of p57 by accelerating turnover rate of p57 and enhancing p57 ubiquitination. Importantly, the negative impact of HER2/Akt on p57 stability contributes to HER2-mediated cell proliferation, transformational activity and tumorigenicity. p57 restoration can attenuate these defects caused by HER2. Significantly, Kaplan-Meier analysis of tumor samples demonstrate that in tumors where HER2 expression was observed, high expression levels of p57 (Kip2) were associated with better overall survival. These data suggest that HER2/Akt is an important negative regulator of p57 (Kip2) , and that p57 restoration in HER2-overexpressing cells can reduce breast tumor growth. Our findings indicate the applicability of employing p57 regulation as a therapeutic intervention in HER2-overexpressing cancers.

MyoD regulates p57kip2 expression by interacting with a distant cis-element and modifying a higher order chromatin structure

The bHLH transcription factor MyoD, the prototypical master regulator of differentiation, directs a complex program of gene expression during skeletal myogenesis. The up-regulation of the cdk inhibitor p57^kip2 plays a critical role in coordinating differentiation and growth arrest during muscle development, as well as in other tissues. p57^kip2 displays a highly specific expression pattern and is subject to a complex epigenetic control driving the imprinting of the paternal allele. However, the regulatory mechanisms governing its expression during development are still poorly understood. We have identified an unexpected mechanism by which MyoD regulates p57^kip2 transcription in differentiating muscle cells. We show that the induction of p57^kip2 requires MyoD binding to a long-distance element located within the imprinting control region KvDMR1 and the consequent release of a chromatin loop involving p57^kip2 promoter. We also show that differentiation-dependent regulation of p57^kip2, while involving a region implicated in the imprinting process, is distinct and hierarchically subordinated to the imprinting control. These findings highlight a novel mechanism, involving the modification of higher order chromatin structures, by which MyoD regulates gene expression. Our results also suggest that chromatin folding mediated by KvDMR1 could account for the highly restricted expression of p57^kip2 during development and, possibly, for its aberrant silencing in some pathologies.

Characterization, tissue expression, and imprinting analysis of the porcine CDKN1C and NAP1L4 genes

CDKN1C and NAP1L4 in human CDKN1C/KCNQ1OT1 imprinted domain are two key candidate genes responsible for BWS (Beckwith-Wiedemann syndrome) and cancer. In order to increase understanding of these genes in pigs, their cDNAs are characterized in this paper. By the IMpRH panel, porcine CDKN1C and NAP1L4 genes were assigned to porcine chromosome 2, closely linked with IMpRH06175 and with LOD of 15.78 and 17.94, respectively. By real-time quantitative RT-PCR and polymorphism-based method, tissue and allelic expression of both genes were determined using F1 pigs of Rongchang and Landrace reciprocal crosses. The transcription levels of porcine CDKN1C and NAP1L4 were significantly higher in placenta than in other neonatal tissues (P < 0.01) although both genes showed the highest expression levels in the lung and kidney of one-month pigs (P < 0.01). Imprinting analysis demonstrated that in pigs, CDKN1C was maternally expressed in neonatal heart, tongue, bladder, ovary, spleen, liver, skeletal muscle, stomach, small intestine, and placenta and biallelically expressed in lung and kidney, while NAP1L4 was biallelically expressed in the 12 neonatal tissues examined. It is concluded that imprinting of CDKN1C is conservative in mammals but has tissue specificity in pigs, and imprinting of NAP1L4 is controversial in mammalian species.

Fetal overgrowth in the Cdkn1c mouse model of Beckwith-Wiedemann syndrome

Mutations in the imprinted CDKN1C gene are associated with the childhood developmental disorder Beckwith-Wiedemann syndrome (BWS). Multiple mouse models with deficiency of Cdkn1c recapitulate some aspects of BWS but do not exhibit overgrowth of the newborn, a cardinal feature of patients with BWS. In this study, we found that Cdkn1c mutants attained a 20% increase in weight during gestation but experienced a rapid reversal of this positive growth trajectory very late in gestation. We observed a marked effect on placental development concurrently with this loss of growth potential, with the appearance of large thrombotic lesions in the labyrinth zone. The trilaminar trophoblast layer that separates the maternal blood sinusoids from fetal capillaries was disordered with a loss of sinusoidal giant cells, suggesting a role for Cdkn1c in maintaining the integrity of the maternal-fetal interface. Furthermore, the overgrowth of mutant pups decreased in the face of increasing intrauterine competition, identifying a role for Cdkn1c in the allocation of the maternal resources via the placenta. This work explains one difficulty in precisely replicating BWS in this animal model: the differences in reproductive strategies between the multiparous mouse, in which intrauterine competition is high, and humans, in which singleton pregnancies are more common.

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.

Beckwith-Wiedemann syndrome

Beckwith-Wiedemann syndrome (BWS) is a model disorder for the study of imprinting, growth dysregulation, and tumorigenesis. Unique observations in this disorder point to an important embryonic developmental window relevant to the observations of increased monozygotic twinning and an increased rate of epigenetic errors after subfertility/assisted reproduction.

Developmental defects and childhood cancer

PURPOSE OF REVIEW

Childhood cancer syndromes are rare but easily recognizable in the clinical setting. Early detection of a potential underlying genetic defect by the general practitioner can be lifesaving. Additionally, important clinical clues that can aid in recognition, or lead to diagnostic referral, for a possible cancer-predisposing syndrome in the individual patient or family are discussed.

RECENT FINDINGS

Recent advancements in genetics have increased our understanding of many genetic developmental pathways involved in cancer predisposition syndromes. Importantly, some of the defects in these pathways can explain the wide phenotypic variability in overall growth, physical dysmorphisms, and cancer risk in children. Genetic testing is now available for many disorders and important guidelines for screening are quickly evolving. The current diagnostic criteria, genetics, and cancer screening guidelines for neurofibromatosis type 1, Beckwith-Wiedemann syndrome/ hemihypertrophy, and PTEN hamartoma tumor syndrome, among others, are reviewed.

SUMMARY

Early recognition of a possible underlying genetic defect with a resultant diagnostic work-up can lessen or prevent tumor burden, improve screening for possible cancer recurrence, and optimize care for children and their family members. Important clues from the history and physical include a family history of cancer, a specific cancer type frequently associated with a genetic defect, synchronous or metachronous cancers in the same individual, growth abnormalities, abnormal skin pigmentation, and/or thumb/radius malformations. Many cases can be recognized by the general practitioner and referred to the appropriate specialists for completion of the diagnostic work-up and recommendations for appropriate management.

p57KIP2: "Kip"ing the cell under control

p57(KIP2) is an imprinted gene located at the chromosomal locus 11p15.5. It is a cyclin-dependent kinase inhibitor belonging to the CIP/KIP family, which includes additionally p21(CIP1/WAF1) and p27(KIP1). It is the least studied CIP/KIP member and has a unique role in embryogenesis. p57(KIP2) regulates the cell cycle, although novel functions have been attributed to this protein including cytoskeletal organization. Molecular analysis of animal models and patients with Beckwith-Wiedemann Syndrome have shown its nodal implication in the pathogenesis of this syndrome. p57(KIP2) is frequently down-regulated in many common human malignancies through several mechanisms, denoting its anti-oncogenic function. This review is a thorough analysis of data available on p57(KIP2), in relation to p21(CIP1/WAF1) and p27(KIP1), on gene and protein structure, its transcriptional and translational regulation, and its role in human physiology and pathology, focusing on cancer development.

CDK inhibitors: cell cycle regulators and beyond

First identified as cell cycle inhibitors mediating the growth inhibitory cues of upstream signaling pathways, the cyclin-CDK inhibitors of the Cip/Kip family p21Cip1, p27Kip1, and p57Kip2 have emerged as multifaceted proteins with functions beyond cell cycle regulation. In addition to regulating the cell cycle, Cip/Kip proteins play important roles in apoptosis, transcriptional regulation, cell fate determination, cell migration and cytoskeletal dynamics. A complex phosphorylation network modulates Cip/Kip protein functions by altering their subcellular localization, protein-protein interactions, and stability. These functions are essential for the maintenance of normal cell and tissue homeostasis, in processes ranging from embryonic development to tumor suppression.

Japanese and North American/European patients with Beckwith-Wiedemann syndrome have different frequencies of some epigenetic and genetic alterations

Beckwith-Wiedemann syndrome (BWS) is an imprinting-related human disease. The frequencies of causative alterations such as loss of methylation (LOM) of KvDMR1, hypermethylation of H19-DMR, paternal uniparental disomy, CDKN1C gene mutation, and chromosome abnormality have been described for North American and European patients, but the corresponding frequencies in Japanese patients have not been measured to date. Analysis of 47 Japanese cases of BWS revealed a significantly lower frequency of H19-DMR hypermethylation and a higher frequency of chromosome abnormality than in North American and European patients. These results suggest that susceptibility to epigenetic and genetic alterations differs between the two groups.

Cdkn1c (p57Kip2) is the major regulator of embryonic growth within its imprinted domain on mouse distal chromosome 7

Background

Cdkn1c encodes an embryonic cyclin-dependant kinase inhibitor that acts to negatively regulate cell proliferation and, in some tissues, to actively direct differentiation. This gene, which is an imprinted gene expressed only from the maternal allele, lies within a complex region on mouse distal chromosome 7, called the IC2 domain, which contains several other imprinted genes. Studies on mouse embryos suggest a key role for genomic imprinting in regulating embryonic growth and this has led to the proposal that imprinting evolved as a consequence of the mismatched contribution of parental resources in mammals.

Results

In this study, we characterised the phenotype of mice carrying different copy number integrations of a bacterial artificial chromosome spanning Cdkn1c. Excess Cdkn1c resulted in embryonic growth retardation that was dosage-dependent and also responsive to the genetic background. Two-fold expression of Cdkn1c in a subset of tissues caused a 10–30% reduction in embryonic weight, embryonic lethality and was associated with a reduction in the expression of the potent, non-imprinted embryonic growth factor, Igf1. Conversely, loss of expression of Cdkn1c resulted in embryos that were 11% heavier with a two-fold increase in Igf1.

Conclusion

We have shown that embryonic growth in mice is exquisitely sensitive to the precise dosage of Cdkn1c. Cdkn1c is a maternally expressed gene and our findings support the prediction of the parental conflict hypothesis that that the paternal genome silences genes that have an inhibitory role in embryonic growth. Within the IC2 imprinted domain, Cdkn1c encodes the major regulator of embryonic growth and we propose that Cdkn1c was the focal point of the selective pressure for imprinting of this domain.

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.

DNAse I pre-treatment markedly enhances detection of nuclear cyclin-dependent kinase inhibitor p57Kip2 and BrdU double immunostaining in embryonic rat brain

As a member of the CIP/KIP family of cyclin-dependent kinase inhibitors (CKIs), p57Kip2 binds tightly to G1 cyclin/cyclin-dependent kinase complexes to block cell cycle progression. CKIs play critical roles in regulating the transition from proliferation to differentiation in many tissues, including the nervous system. Conversely, CKI dys-regulation contributes to neoplasia and cancer progression. While the combined detection of CKI immunoreactivity and S phase entry using bromodeoxyuridine (BrdU) incorporation may be particularly informative, successful immunostaining may be limited due to "masked" antigen epitopes and acid-induced signal degradation. We now report an improved double immunofluorescent method for detecting p57Kip2 and BrdU in paraformaldehyde-fixed frozen sections of embryonic rat brain. We substituted deoxyribonuclease I (DNAse I) for HCl pre-treatment to expose antigenic sites in frozen sections, and employed a biotinylated tyramide-based system to enhance p57Kip2 visualization. We identified a time- and dose-dependent relationship between DNAse I treatment and double labeling of p57Kip2 and BrdU, increasing both the numbers and intensities of immunopositive nuclei. With excess DNAse I treatment, however, there was signal degradation for both BrdU and total DNA, as reflected by DAPI staining. The use of DNAse I pre-treatment significantly increases the reliability and sensitivity of immunodetection of CKI nuclear factors, and should be useful for both developmental neurobiology studies as well as cancer diagnostic applications.

Beckwith-Wiedemann syndrome

Beckwith-Wiedemann syndrome (BWS) is a clinically heterogeneous overgrowth syndrome associated with an increased risk for embryonal tumor development. BWS provides an ideal model system to study epigenetic mechanisms. This condition is caused by a variety of genetic or epigenetic alterations within two domains of imprinted growth regulatory genes on human chromosome 11p15. Molecular studies of BWS have provided important data with respect to epigenotype/genotype-phenotype correlations; for example, alterations of Domain 1 are associated with the highest risk for tumor development, specifically Wilms' tumor. Further, the elucidation of the molecular basis for monozygotic twinning in BWS defined a critical period for imprint maintenance during pre-implantation embryonic development. In the future, such molecular studies in BWS will permit enhanced medical management and targeted genetic counseling.

Risk of tumorigenesis in overgrowth syndromes: a comprehensive review

Overgrowth syndromes (OGS) comprise a heterogeneous group of disorders in which the main characteristic is that either weight, height, or head circumference is 2-3 standard deviations (SD) above the mean for sex and age. A striking feature of OGS is the risk of neoplasms. Here, the relative frequency of specific tumors in each OGS, topographic location, and age of appearance is determined by reviewing published cases. In some OGS (Perlman, Beckwith-Wiedemann, and Simpson-Golabi-Behmel syndromes and hemihyperplasia) more than 94% of tumors appeared in the abdomen usually before 10 years of age, mainly embryonal in type. In Perlman syndrome, only Wilms tumor has been recorded, whereas in Sotos syndrome, lympho-hematologic tumors are most frequent. Based on literature review, a specific schedule protocol for tumor screening is suggested for each OGS. A schedule with different intervals and specific tests is proposed for a more rational cost/benefit program for these disorders.

Studies of variations of the cyclin-dependent kinase inhibitor 1C and the cyclin-dependent kinase 4 genes in relation to type 2 diabetes mellitus and related quantitative traits

CDK4 is involved in the regulation of body weight, pancreatic beta-cell proliferation, insulin responsiveness, and diabetes pathogenesis. CDK4 activity is inhibited by CDKN1C, which is regulated by insulin. In addition, CDKN1C plays an important role in beta-cell proliferation and is involved in the pathogenesis of the Beckwith-Wiedemann syndrome, a disorder characterized by neonatal hyperinsulinaemic hypoglycaemia and pre- and post-natal overgrowth. The aim of this study was to investigate if variations in the proximal promoter and the coding region of the CDKN1C and CDK4 genes are associated with type 2 diabetes or changes in related quantitative phenotypes among glucose-tolerant subjects. Mutation analyses of the two genes in 62 type 2 diabetic patients resulted in the discovery of seven variants of CDKN1C and two variants of CDK4. In a case-control study comprising 717 type 2 diabetic patients and 518 glucose-tolerant subjects the most frequent variants did not show any difference in allele frequencies between the type 2 diabetic patients and the control subjects. However, in two genotype-quantitative trait correlation studies involving 206 glucose-tolerant offspring of type 2 diabetic patients and 359 young, healthy subjects the CDKN1C del171APVA variant associated with increased birth weight (P=0.05 and P=0.05). Furthermore, the same variant tended to be associated with decreased basal glucose oxidation among 16 genotypically discordant dizygotic twins (P=0.03). In a genotype-quantitative trait study involving 500 middle-aged glucose-tolerant subjects the CDK4 IVS2-31G-->A variant was associated with an increased waist circumference (P=0.03) and waist-to-hip ratio (P=0.02) and altered fasting plasma glucose (P=0.03). However, these later findings could not be replicated in additional studies. In conclusion, variants in CDKN1C may contribute to the inter-individual variation in birth weight.

CDKN1C mutation in Wiedemann-Beckwith syndrome patients reduces RNA splicing efficiency and identifies a splicing enhancer

Wiedemann-Beckwith syndrome (WBS) is a human overgrowth disorder that is accompanied by an increased risk of embryonal tumors and is associated with dsyregulation of the imprinting of genes in chromosome 11p15.5. Maternally inherited mutations in the imprinted CDKN1C gene are known to be associated with WBS. We have identified a novel mutation in several members of a large family affected by WBS. The mutation is a G --> T change in a run of seven G's near the 5' splice site of intron 3. All obligate carriers and affected individuals carry the mutation, and in each affected case, the allele was inherited maternally, strongly suggesting a role in causing WBS. The mutation is located in a poly-G tract in the intron; intronic G-rich sequences in other genes have been shown to have a role in promoting splicing. In transfected 293HEK cells, we found that the G --> T mutation reduced splicing efficiency. Mutation of all seven G's in the poly-G tract further reduced splicing efficiency, supporting a role for the G-tract as a splicing enhancer. The fibroblasts of one affected patient showed a similar reduction in splicing efficiency. Maternal monoallelic expression of CDKN1C was verified in this patient cell line. However, the total amount of spliced message was not reduced by the mutation in spite of the reduced efficiency of splicing. We discuss the possible role of the splicing defect in the pathogenesis of WBS in this pedigree.

Multiple mechanisms downregulateCDKN1C in human bladder cancer

Expression of the imprinted CDKN1C gene at chromosome 11p15.5 encoding the cell cycle inhibitor p57(KIP2) is disturbed in Beckwith-Wiedemann syndrome and in several human cancers by different mechanisms. Many advanced urothelial cancers (TCC) display downregulation of CDKN1C expression. The responsible mechanisms were investigated in TCC cell lines, with cultured normal urothelial cells (UEC) as controls. CDKN1C mRNA expression was diminished in 12/15 TCC lines and p57(KIP2) protein was decreased accordingly. Because CDKN1C is expressed from the maternal allele only, LOH at 11p15.5 represents one mechanism of downregulation. In 3 cell lines, several polymorphic markers flanking CDKN1C were homozygous compatible with this mechanism. Hypermethylation of the CDKN1C promoter, a reported cause of downregulation in other cancers, was detected by bisulfite sequencing in several cell lines and appeared associated with downregulation in at least one cell line. The methylation inhibitor 5-aza-2'deoxycytidine induced CDKN1C expression in this cell line and others. A third reported mechanism involves a switch of both alleles toward a paternal imprinting pattern, indicated by hypomethylation of a differentially methylated region (DMR) in the imprinting center (IC2). This hypomethylation was detected in most TCC lines, and was associated with re-expression of the non-coding LIT1 RNA and with downregulation of CDKN1C in several. Thus, CDKN1C downregulation in TCC seems to occur by several different mechanisms. This finding and the ability of p57(KIP2) to induce senescence in urothelial cells make CDKN1C a good candidate for a tumor suppressor at 11p in TCC.

A fluorescent method for detecting low-grade 11patUPD mosaicism in Beckwith–Wiedemann syndrome

The quantitative evaluation of mosaicism for uniparental disomy (UPD) involving a restricted chromosomal region requires the availability of a sensitive and reproducible method that is capable of detecting even a small percentage of disomic cells and avoiding false positive and false negative results. The occurrence of UPD is usually monitored by means of the parent-proband segregation analysis of microsatellites mapping to the target region. We here describe the quantitative blood cell evaluation of segmental mosaic UPD11, a marker of Beckwith-Wiedemann syndrome, by means of the segregation analysis of 11p15 microsatellites using both radioactive and fluorescence-based techniques. As the greater amplification efficiency of the shorter allele in heterozygous subjects may bias the correct evaluation of disomy, the mean short/long allele ratio was established at three loci of each of 30 normal heterozygous subjects, as well as the peak As/Al area in the presence of 50% of each allele. The interval was defined using a 5% level of significance. The results show that the fluorescence-based technique is superior to radioactivity in detecting the subtle allelic imbalances present in low-grade mosaicism conditions.

p57KIP2 modulates stress-activated signaling by inhibiting c-Jun NH2-terminal kinase/stress-activated protein Kinase

p57KIP2, a member of the Cip/Kip family of enzymes that inhibit several cyclin-dependent kinases, plays a role in many biological events including cell proliferation, differentiation, apoptosis, tumorigenesis and developmental changes. The human p57KIP2 gene is located in chromosome 11p15.5, a region implicated in sporadic cancers and Beckwith-Wiedemann syndrome. We here report that p57KIP2 physically interacts with and inhibits c-Jun NH2-terminal kinase/stress-activated protein kinase (JNK/SAPK). The carboxyl-terminal QT domain of p57KIP2 is crucial for the inhibition of JNK/SAPK. Overexpressed p57KIP2 also suppressed UV- and MEKK1-induced apoptotic cell death. p57KIP2 expression during C2C12 myoblast differentiation resulted in repression of the JNK activity stimulated by UV light. Furthermore, UV-stimulated JNK1 activity was higher in mouse embryonic fibroblasts derived from p57-/- mice than in the cells from wild-type mice. Taken together, these findings suggest that p57KIP2 modulates stress-activated signaling by functioning as an endogenous inhibitor of JNK/SAPK.

Microarray analysis of uterine gene expression in mouse and human pregnancy

Improved care of infants born prematurely has increased their survival. However, the incidence of preterm labor has not changed. To understand the processes involved in preterm labor, we used oligonucleotide microarrays to study gene expression in murine and human uterus during pregnancy. The induction of enzymes for prostaglandin synthesis was used as a marker for important changes during pregnancy because prostaglandins strongly contribute to both human and murine labor. We identified 504 genes that changed at least 2-fold between d 13.5 and 19.0 in the gravid mouse uterus. In the pregnant human myometrium, we found 478 genes that changed at least 2-fold in either term or preterm labor compared with preterm nonlabor specimens and 77 genes that significantly varied in both preterm and term labor. Patterns of gene regulation within functional groups comparing human preterm and term labor were similar, although the magnitude of change often varied. Surprisingly, few genes that changed significantly throughout pregnancy were the same in the mouse and human. These data suggest that functional progesterone withdrawal in human myometrium may not be the primary mechanism for labor induction, may implicate similar mechanisms for idiopathic preterm and term labor in humans, and may identify novel targets for further study.

Insulator and silencer sequences in the imprinted region of human chromosome 11p15.5

The imprinting of the genes on human chromosome 11p15.5 is thought to be controlled by two imprinting control regions located in two differentially methylated CpG islands upstream of the H19 gene (H19 DMR) and in intron 10 of the KCNQ1 gene (KvDMR). We have examined sequences in the human 11p15.5 genomic imprinted region for the presence of insulators and silencers using a position- and enhancer-dependent stable transfection assay. We have confirmed the existence of insulators in H19 DMR and discovered two novel insulators in the IGF2 gene. We have also found two novel silencer sequences; one is located in KvDMR, a region that is thought to contain the promoter for the KCNQ1OT1 transcript, and another is in the CDKN1C gene. We have demonstrated binding of CTCF protein in vitro to all the insulator and silencer sequences that we have detected. We discuss the differences in the regulation of imprinting controlled by the two imprinting control regions in chromosome 11p.

Physiological functions of imprinted genes

Genomic imprinting in gametogenesis marks a subset of mammalian genes for parent-of-origin-dependent monoallelic expression in the offspring. Embryological and classical genetic experiments in mice that uncovered the existence of genomic imprinting nearly two decades ago produced abnormalities of growth or behavior, without severe developmental malformations. Since then, the identification and manipulation of individual imprinted genes has continued to suggest that the diverse products of these genes are largely devoted to controlling pre- and post-natal growth, as well as brain function and behavior. Here, we review this evidence, and link our discussion to a website (http://www.otago.ac.nz/IGC) containing a comprehensive database of imprinted genes. Ultimately, these data will answer the long-debated question of whether there is a coherent biological rationale for imprinting.

Linkage study in families with posterior helical ear pits and Wiedemann-Beckwith syndrome

The Wiedemann-Beckwith syndrome (WBS) is defined by a group of anomalies, including macrosomia, macroglossia, omphalocele, and ear creases. Several minor anomalies have also been reported in the syndrome, including posterior helical ear pits (PHEP). Two independent linkage studies of pedigrees with autosomal dominant inheritance have shown linkage of WBS to 11p15.5 markers. Further confirming the location of WBS to this location is the finding of 11p15.5 duplications and translocations, as well as uniparental disomy for a small area of 11p15.5. In this study, members of previously described families exhibiting autosomal dominant inheritance of the PHEP phenotype were genotyped for three markers in the 11p15.5 region. These three markers were in the insulin-like growth factor (IGF2), insulin (INS), and tyrosine hydroxylase (TH) region. The data were examined by linkage analysis using the same genetic model used previously to demonstrate linkage of WBS to markers on chromosome 11p15.5: an autosomal dominant model with a penetrance of 0.90 and a gene frequency of 0.001. In one large pedigree, linkage analysis of the 11p15.5 markers excluded the PHEP phenotype from the IGF2, INS, and TH region. In the four other pedigrees examined, the marker loci were not sufficiently informative or the pedigrees did not provide sufficient power to exclude linkage from this region. The strongest evidence against linkage of the PHEP phenotype to 11p15.5 was evident by inspection of the segregation of the haplotypes of the markers in the pedigrees. In two informative pedigrees, relatives with the PHEP phenotype did not share the same haplotype of markers identical by descent. Our results show that the PHEP phenotype is not linked to chromosome 11p15.5 in the informative families tested. In the families examined, there are not enough individuals with WBS to determine if WBS was linked to 11p15.5 in these families. Although locus heterogeneity has not been demonstrated in WBS, it is possible that a second WBS locus exists and that the PHEP phenotype in these families is linked to a second WBS locus. Alternatively, the PHEP phenotype may occur independently of WBS so that the association of WBS and PHEP in our pedigrees may, in fact, represent causal heterogeneity.

Genetic background of adrenocortical tumor development

The increasing occurrence of incidentally discovered benign adrenocortical tumors has become a clinical dilemma because of the difficulties in differentiating them from their malignant counterpart. Adrenocortical tumors are associated with familial cancer syndromes such as the Beckwith-Wiedemann syndrome, the Li-Fraumeni syndrome, the Carney complex, multiple endocrine neoplasia type 1, congenital adrenal hyperplasia, and the McCune-Albright syndrome. Genetic events are known to take place on the chromosomal and gene level in sporadic adrenocortical tumors.

Imprinting status of 11p15 genes in Beckwith-Wiedemann syndrome patients with CDKN1C mutations

Beckwith-Wiedemann syndrome (BWS) is an imprinting disorder characterized by somatic overgrowth, congenital malformations, and predisposition to childhood tumors. Aberrant expression of multiple imprinted genes, including H19, IGF2, KCNQ1OT1, and CDKN1C, has been observed in BWS patients. It has been estimated that mutations in CDKN1C occur in 12-17% of BWS patients. We have screened 10 autosomal dominant pedigrees and 65 sporadic BWS cases by PCR/heteroduplex analysis and DNA sequencing and have identified four mutations, two of which were associated with biallelic IGF2 expression and normal H19 and KCNQ1OT1 imprinting. One patient demonstrated phenotypic expression of paternally transmitted mutation in this maternally expressed gene, a second proband is the child of one of a pair of monozygotic twin females who carry the mutation de novo, and a third patient exhibited unusual skeletal changes more commonly found in other overgrowth syndromes. When considered with other studies published to date, this work reveals the frequency of CDKN1C mutations in BWS to be only 4.9%. This is the first report of an analysis of the imprinting status of genes in the 11p15 region where CDKN1C mutations were associated with loss of IGF2 imprinting and maintenance of H19 and KCNQ1OT1 imprinting.

Epigenotype-phenotype correlations in Beckwith-Wiedemann syndrome

Beckwith-Wiedemann syndrome (BWS) is a model imprinting disorder resulting from mutations or epigenetic events involving imprinted genes at chromosome 11p15.5. Thus, germline mutations in CDKN1C, uniparental disomy (UPD), and loss of imprinting of IGF2 and other imprinted genes have been implicated. Many familial BWS cases have germline CDKN1C mutations. However, most BWS cases are sporadic and UPD or putative imprinting errors predominate in this group. We have identified previously a subgroup of sporadic cases with loss of imprinting (LOI) of IGF2 and epigenetic silencing of H19 proposed to be caused by a defect in a distal 11p15.5 imprinting control element (designated BWSIC1). However, many sporadic BWS patients show biallelic IGF2 expression in the presence of normal H19 methylation and expression patterns. This and other evidence suggested the existence of a further imprinting control element (BWSIC2) at 11p15. 5. Recently, we showed that a subgroup of BWS patients have loss of methylation (LOM) at a differentially methylated region (KvDMR1) within the KCNQ1 gene centromeric to the IGF2 and H19 genes. We have now analysed a large series of sporadic cases to define the frequency and phenotypic correlates of epigenetic abnormalities in BWS. LOM at KvDMR1 was detected by Southern analysis or a novel PCR based method in 35 of 69 (51%) sporadic BWS without UPD. LOM at KvDMR1 was often, but not invariably associated with LOI of IGF2. KvDMR1 LOM was not detected in BWS patients with putative BWSIC1 defects and cases with KvDMR1 LOM (that is, putative BWSIC2 defects) invariably had a normal H19 methylation pattern. The incidence of exomphalos in putative BWSIC2 defect patients was not significantly different from that in patients with germline CDKN1C mutations (20/29 and 13/15 respectively), but was significantly greater than that in patients with putative BWSIC1 defects (0/5, p=0.007) and UPD (0/22, p<0.0001). These findings are consistent with the hypothesis that LOM of KvDMR1 (BWSIC2 defect) results in epigenetic silencing of CDKN1C and variable LOI of IGF2. BWS patients with embryonal tumours have UPD or a BWSIC1 defect but not LOM of KvDMR1. This study has further shown how (1) variations in phenotypic expression of BWS may be linked to specific molecular subgroups and (2) molecular analysis of BWS can provide insights into mechanisms of imprinting regulation.

p57(KIP2) is not mutated in hepatoblastoma but shows increased transcriptional activity in a comparative analysis of the three imprinted genes p57(KIP2), IGF2, and H19

Hepatoblastomas (HBs), representing malignant liver tumors of childhood, show frequent loss of heterozygosity (LOH) in the chromosomal region 11p15.5. This loss is of maternal origin suggesting the presence of a monoallelically expressed tumor suppressor gene in this region. p57(KIP2) (KIP2) located at 11p15.5 is predominantly expressed from the maternal allele and encodes a cyclin-dependent kinase inhibitor. We screened a series of 56 HB tumors and five HB cell lines for allelic loss (LOH) of the KIP2 locus by microsatellite analysis and KIP2 coding sequence mutations by single-strand conformation polymorphism analysis. Although LOH at the KIP2 locus occurred in 25% of the cases, no mutations were found. Analysis of KIP2 mRNA expression by competitive reverse transcriptase-polymerase chain reaction revealed up-regulation in nine of 12 HBs compared to matching liver samples. In contrast, mRNA levels of the putative suppressor gene H19 on 11p15.5 were decreased in 10 of 12 tumors, indicating that KIP2 and H19 are not co-regulated in HBs. IGF2 mRNA expression was increased in 11 of 12 HB samples. All HBs showed monoallelic KIP2 expression. However, the overexpression of KIP2 in HBs with maternal loss of 11p15.5 suggests a reactivation of the paternal allele in these cases. Overexpression of KIP2 in HBs argues against a role as a HB suppressor gene.

P27 in cell cycle control and cancer

In order to survive, cells need tight control of cell cycle progression. The control mechanisms are often lost in human cancer cells. The cell cycle is driven forward by cyclin-dependent kinases (CDKs). The CDK inhibitors (CKIs) are important regulators of the CDKs. As the name implies, CKIs were initially shown to negatively regulate CDK activity. However, recent data indicates that the members of the Kip/Cip family of CKIs, including p27, exert both positive and negative regulation of CDK activity at the G1/S phase transition. Mutations of Kip/Cip genes are rare, but p27 knockout mice are tumor prone when challenged with carcinogenic stimuli. Numerous studies of various human non-hematological tumors have identified low expression of p27 as a predictor of poor prognosis. In non-Hodgkin's lymphoma (NHL), we and others have also shown the independent prognostic value of p27 expression. In distinct NHL entities however, shortened survival seems to correlate with high expression of p27. For definitive assessment of the role played by p27 in lymphomagenesis, and the prognostic value of p27 in these tumors, further studies of distinct NHL entities are needed. This review addresses the function of p27 and the other Kip/Cip proteins in G1/S phase transition and their possible role in tumorigenesis with emphasis on p27 and NHL.

Analysis of CDKN1C in Beckwith Wiedemann syndrome

In this study we have examined 32 patients with Beckwith Wiedemann Syndrome (BWS) for mutations affecting the CDKN1C gene, including seven cases of familial BWS. Mutations were not detected in the coding region of the CDKN1C gene in any individual with BWS. However in two patients, two G/A base substitutions at adjacent positions in the 5'UTR were detected. These substitutions were also found in normal controls. Expression of CDKN1C in somatic tissues was examined in 18 of the 32 cases using semi-quantitative RT-PCR. CDKN1C expression was significantly reduced in the peripheral blood of three cases compared with controls. These results suggest that, although coding region mutations in the CDKN1C gene are rare in BWS, mutations disrupting CDKN1C expression may be found. Three of five informative patients exhibited biallelic CDKN1C expression in lymphocytes, cord blood, and kidney tissue, respectively. Biallelic expression was not associated with overall CDKN1C levels significantly different to those in controls. Patients who expressed CDKN1C biallelically, or who were low CDKN1C expressors, maintained monoallelic methylation in the Differentially Methylated Region 2 (DMR2) of the IGF2 locus. One patient expressing CDKN1C biallelically, maintained imprinted gene expression at the IGF2 locus. These results suggest that biallelic CDKN1C expression does not significantly perturb the overall levels of CDKN1C expression in somatic tissue. They also confirm other studies showing that the mechanisms associated with regulating CDKN1C expression and imprinting are separate from those regulating IGF2 imprinting.

Alterations of H19 imprinting and IGF2 replication timing are infrequent in Beckwith-Wiedemann syndrome

Beckwith-Wiedemann syndrome (BWS) is an overgrowth disorder resulting from dysregulation of multiple imprinted genes through a variety of distinct mechanisms. A frequent alteration in BWS involves changes in the imprinting status of the coordinately regulated IGF2 and H19 genes on 11p15. Patients have been categorized according to alterations in the imprinted expression, allele-specific methylation, and regional replication timing of these genes. In this work, IGF2/H19 expression, H19 DNA methylation, and IGF2 regional replication timing were studied in nine karyotypically normal BWS fibroblasts and two BWS patients with maternally inherited 11p15 chromosomal rearrangements. Informative patients (9/9) maintained normal monoallelic H19 expression/methylation, despite biallelic IGF2 expression in 6/9. Replication timing studies revealed no changes in the pattern of asynchronous replication timing for both a patient with biallelic IGF2 expression and a patient carrying an 11p15 inversion. In contrast, a patient with a chromosome 11;22 translocation and normal H19 expression/methylation exhibited partial loss of asynchrony and a shift toward earlier replication times. These results indicate that in BWS, (1) H19 imprinting alterations are less frequent than previously estimated, (2) IGF2 imprinting and H19 imprinting are not necessarily coordinated, and (3) alterations in regional replication timing are generally not correlated with either chromosomal rearrangements or the imprinting status of IGF2 and H19.

Analysis of germline CDKN1C (p57KIP2) mutations in familial and sporadic Beckwith-Wiedemann syndrome (BWS) provides a novel genotype-phenotype correlation

Beckwith-Wiedemann syndrome (BWS) is a human imprinting disorder with a variable phenotype. The major features are anterior abdominal wall defects including exomphalos (omphalocele), pre- and postnatal overgrowth, and macroglossia. Additional less frequent complications include specific developmental defects and a predisposition to embryonal tumours. BWS is genetically heterogeneous and epigenetic changes in the IGF2/H19 genes resulting in overexpression of IGF2 have been implicated in many cases. Recently germline mutations in the cyclin dependent kinase inhibitor gene CDKN1C (p57KIP2) have been reported in a variable minority of BWS patients. We have investigated a large series of familial and sporadic BWS patients for evidence of CDKN1C mutations by direct gene sequencing. A total of 70 patients with classical BWS were investigated; 54 were sporadic with no evidence of UPD and 16 were familial from seven kindreds. Novel germline CDKN1C mutations were identified in five probands, 3/7 (43%) familial cases and 2/54 (4%) sporadic cases. There was no association between germline CDKN1C mutations and IGF2 or H19 epigenotype abnormalities. The clinical phenotype of 13 BWS patients with germline CDKN1C mutations was compared to that of BWS patients with other defined types of molecular pathology. This showed a significantly higher frequency of exomphalos in the CDKN1C mutation cases (11/13) than in patients with an imprinting centre defect (associated with biallelic IGF2 expression and H19 silencing) (0/5, p<0.005) or patients with uniparental disomy (0/9, p<0.005). However, there was no association between germline CDKN1C mutations and risk of embryonal tumours. No CDKN1C mutations were identified in six non-BWS patients with overgrowth and Wilms tumour. These findings (1) show that germline CDKN1C mutations are a frequent cause of familial but not sporadic BWS, (2) suggest that CDKN1C mutations probably cause BWS independently of changes in IGF2/H19 imprinting, (3) provide evidence that aspects of the BWS phenotype may be correlated with the involvement of specific imprinted genes, and (4) link genotype-phenotype relationships in BWS and the results of murine experimental models of BWS.

Two novel genes in the center of the 11p15 imprinted domain escape genomic imprinting

We previously reported the isolation of a 2.5 Mb tumor-suppressing subchromosomal transferable fragment (STF) from human chromosome 11p15 and the identification of nine known genes and four novel genes within this STF. We now report the isolation of two novel cDNAs, designated here as TSSC4 and TSSC6 (tumor-suppressing STF cDNA 4 and 6), located within the STF. TSSC4 and TSSC6 encode predicted proteins of 329 and 290 amino acids, respectively, with no close similarity to previously reported proteins. TSSC4 and TSSC6 are both located in the center of a 1 Mb imprinted domain, which contains the imprinted genes TSSC3, TSSC5, p57(KIP2), KVLQT1, ASCL2, IGF2 and H19. However, we found that neither TSSC4 nor TSSC6 was significantly imprinted in any of the fetal or extra-embryonic tissues examined. Based on this result, the imprinted gene domain of 11p15 appears to contain at least two imprinted subdomains, between which TSSC4 and TSSC6 substantially escape imprinting, due either to lack of initial silencing or to an early developmental relaxation of imprinting.

Genomic imprinting: concept and clinical consequences

One of the major discoveries in modern genetics is the phenomenon of genomic, or parental, imprinting. The parent-of-origin effects seen after transmission of an imprinted gene from parents to their children do not follow the genetic rules postulated by Gregor Mendel. This has obvious consequences for genetic counselling. Aberrant imprinting can lead to a wide variety of clinical disorders ranging from the development of tumours to pronounced growth abnormalities and from mental retardation to developmental disorders of language or autism as seen in Turner's syndrome. Here we describe the basic principles of genomic imprinting and discuss a number of well-characterized clinical disorders associated with genomic imprinting.