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Matarazzo V, Muscatelli F. Natural breaking of the maternal silence at the mouse and human imprinted Prader-Willi locus: A whisper with functional consequences. Rare Dis 2013; 1:e27228. [PMID: 25003016 PMCID: PMC3978896 DOI: 10.4161/rdis.27228] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2013] [Revised: 11/15/2013] [Accepted: 11/15/2013] [Indexed: 12/22/2022] Open
Abstract
Genomic imprinting is a normal process of epigenetic regulation leading some autosomal genes to be expressed from one parental allele only, the other parental allele being silenced. The reasons why this mechanism has been selected throughout evolution are not clear; however, expression dosage is critical for imprinted genes. There is a paradox between the fact that genomic imprinting is a robust mechanism controlling the expression of specific genes and the fact that this mechanism is based on epigenetic regulation that, per se, should present some flexibility. The robustness has been well studied, revealing the epigenetic modifications at the imprinted locus, but the flexibility has been poorly investigated.
Prader-Willi syndrome is the best-studied disease involving imprinted genes caused by the absence of expression of paternally inherited alleles of genes located in the human 15q11-q13 region. Until now, the silencing of the maternally inherited alleles was like a dogma. Rieusset et al. showed that in absence of the paternal Ndn allele, in Ndn +m/-p mice, the maternal Ndn allele is expressed at an extremely low level with a high degree of non-genetic heterogeneity. In about 50% of these mutant mice, this stochastic expression reduces birth lethality and severity of the breathing deficiency, correlated with a reduction in the loss of serotonergic neurons. Furthermore, using several mouse models, they reveal a competition between non-imprinted Ndn promoters, which results in monoallelic (paternal or maternal) Ndn expression, suggesting that Ndn monoallelic expression occurs in the absence of imprinting regulation. Importantly, specific expression of the maternal NDN allele is also detected in post-mortem brain samples of PWS individuals. Here, similar expression of the Magel2 maternal allele is reported in Magel2 +m/-p mice, suggesting that this loss of imprinting can be extended to other PWS genes. These data reveal an unexpected epigenetic flexibility of PWS imprinted genes that could be exploited to reactivate the functional but dormant maternal alleles in PWS.
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Rieusset A, Schaller F, Unmehopa U, Matarazzo V, Watrin F, Linke M, Georges B, Bischof J, Dijkstra F, Bloemsma M, Corby S, Michel FJ, Wevrick R, Zechner U, Swaab D, Dudley K, Bezin L, Muscatelli F. Stochastic loss of silencing of the imprinted Ndn/NDN allele, in a mouse model and humans with prader-willi syndrome, has functional consequences. PLoS Genet 2013; 9:e1003752. [PMID: 24039599 PMCID: PMC3764186 DOI: 10.1371/journal.pgen.1003752] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2013] [Accepted: 07/10/2013] [Indexed: 12/27/2022] Open
Abstract
Genomic imprinting is a process that causes genes to be expressed from one allele only according to parental origin, the other allele being silent. Diseases can arise when the normally active alleles are not expressed. In this context, low level of expression of the normally silent alleles has been considered as genetic noise although such expression has never been further studied. Prader-Willi Syndrome (PWS) is a neurodevelopmental disease involving imprinted genes, including NDN, which are only expressed from the paternally inherited allele, with the maternally inherited allele silent. We present the first in-depth study of the low expression of a normally silent imprinted allele, in pathological context. Using a variety of qualitative and quantitative approaches and comparing wild-type, heterozygous and homozygous mice deleted for Ndn, we show that, in absence of the paternal Ndn allele, the maternal Ndn allele is expressed at an extremely low level with a high degree of non-genetic heterogeneity. The level of this expression is sex-dependent and shows transgenerational epigenetic inheritance. In about 50% of mutant mice, this expression reduces birth lethality and severity of the breathing deficiency, correlated with a reduction in the loss of serotonergic neurons. In wild-type brains, the maternal Ndn allele is never expressed. However, using several mouse models, we reveal a competition between non-imprinted Ndn promoters which results in monoallelic (paternal or maternal) Ndn expression, suggesting that Ndn allelic exclusion occurs in the absence of imprinting regulation. Importantly, specific expression of the maternal NDN allele is also detected in post-mortem brain samples of PWS individuals. Our data reveal an unexpected epigenetic flexibility of PWS imprinted genes that could be exploited to reactivate the functional but dormant maternal alleles in PWS. Overall our results reveal high non-genetic heterogeneity between genetically identical individuals that might underlie the variability of the phenotype.
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Affiliation(s)
- Anne Rieusset
- INSERM, Institut de Neurobiologie de la Méditerranée (INMED) U901, Marseille, France
- Aix-Marseille Université, INMED UMR901, Marseille, France
| | - Fabienne Schaller
- INSERM, Institut de Neurobiologie de la Méditerranée (INMED) U901, Marseille, France
- Aix-Marseille Université, INMED UMR901, Marseille, France
| | - Unga Unmehopa
- Netherlands Institute for Neuroscience, an Institute of the Royal Netherlands Academy of Arts and Sciences, Amsterdam, The Netherlands
| | - Valery Matarazzo
- INSERM, Institut de Neurobiologie de la Méditerranée (INMED) U901, Marseille, France
- Aix-Marseille Université, INMED UMR901, Marseille, France
| | - Françoise Watrin
- INSERM, Institut de Neurobiologie de la Méditerranée (INMED) U901, Marseille, France
- Aix-Marseille Université, INMED UMR901, Marseille, France
| | - Matthias Linke
- Universitätsmedizin der Johannes Gutenberg-Universität Mainz Institut für Humangenetik, Mainz, Germany
| | - Beatrice Georges
- INSERM, U1028, CNRS, UMR5292, Université Claude Bernard Lyon 1, Lyon Neuroscience Center, Villeurbanne, France
| | - Jocelyn Bischof
- Department of Medical Genetics, University of Alberta, Edmonton, Alberta, Canada
| | - Femke Dijkstra
- Netherlands Institute for Neuroscience, an Institute of the Royal Netherlands Academy of Arts and Sciences, Amsterdam, The Netherlands
| | - Monique Bloemsma
- Netherlands Institute for Neuroscience, an Institute of the Royal Netherlands Academy of Arts and Sciences, Amsterdam, The Netherlands
| | - Severine Corby
- INSERM, Institut de Neurobiologie de la Méditerranée (INMED) U901, Marseille, France
- Aix-Marseille Université, INMED UMR901, Marseille, France
| | - François J. Michel
- INSERM, Institut de Neurobiologie de la Méditerranée (INMED) U901, Marseille, France
- Aix-Marseille Université, INMED UMR901, Marseille, France
| | - Rachel Wevrick
- Department of Medical Genetics, University of Alberta, Edmonton, Alberta, Canada
| | - Ulrich Zechner
- Universitätsmedizin der Johannes Gutenberg-Universität Mainz Institut für Humangenetik, Mainz, Germany
| | - Dick Swaab
- Netherlands Institute for Neuroscience, an Institute of the Royal Netherlands Academy of Arts and Sciences, Amsterdam, The Netherlands
| | - Keith Dudley
- INSERM, Institut de Neurobiologie de la Méditerranée (INMED) U901, Marseille, France
- Aix-Marseille Université, INMED UMR901, Marseille, France
| | - Laurent Bezin
- INSERM, U1028, CNRS, UMR5292, Université Claude Bernard Lyon 1, Lyon Neuroscience Center, Villeurbanne, France
| | - Françoise Muscatelli
- INSERM, Institut de Neurobiologie de la Méditerranée (INMED) U901, Marseille, France
- Aix-Marseille Université, INMED UMR901, Marseille, France
- * E-mail:
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Abstract
Prader-Willi syndrome (PWS) is a neurodevelopmental disorder that arises from lack of expression of paternally inherited genes known to be imprinted and located in the chromosome 15q11-q13 region. PWS is considered the most common syndromal cause of life-threatening obesity and is estimated at 1 in 10,000 to 20,000 individuals. A de novo paternally derived chromosome 15q11-q13 deletion is the cause of PWS in about 70% of cases, and maternal disomy 15 accounts for about 25% of cases. The remaining cases of PWS result either from genomic imprinting defects (microdeletions or epimutations) of the imprinting centre in the 15q11-q13 region or from chromosome 15 translocations. Here, we describe the clinical presentation of PWS, review the current understanding of causative cytogenetic and molecular genetic mechanisms, and discuss future directions for research.
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Affiliation(s)
- Douglas C Bittel
- Section of Medical Genetics and Molecular Medicine, Children's Mercy Hospitals and Clinics, and University of Missouri-Kansas City School of Medicine, 2401 Gillham Rd, Kansas City, MO 64108, USA.
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Chamberlain SJ, Johnstone KA, DuBose AJ, Simon TA, Bartolomei MS, Resnick JL, Brannan CI. Evidence for genetic modifiers of postnatal lethality in PWS-IC deletion mice. Hum Mol Genet 2004; 13:2971-7. [PMID: 15459179 DOI: 10.1093/hmg/ddh314] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Prader-Willi syndrome (PWS), most notably characterized by infantile hypotonia, short stature and morbid obesity, results from deficiencies in multiple genes that are subject to genomic imprinting. The usefulness of current mouse models of PWS has been limited by postnatal lethality in affected mice. Here, we report the survival of the PWS-imprinting center (IC) deletion mice on a variety of strain backgrounds. Expression analyses of the genes affected in the PWS region suggest that while there is low-level expression from both parental alleles in PWS-IC deletion pups, this expression does not explain their survival on certain strain backgrounds. Rather, the data provide evidence for strain-specific modifier genes that support the survival of PWS-IC deletion mice.
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Affiliation(s)
- Stormy J Chamberlain
- Department of Molecular Genetics and Microbiology, University of Florida College of Medicine, Gainesville, FL 32610, USA
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Lobo-Menendez F, Sossey-Alaoui K, Bell JM, Copeland-Yates SA, Plank SM, Sanford SO, Skinner C, Simensen RJ, Schroer RJ, Michaelis RC. Absence of MeCP2 mutations in patients from the South Carolina autism project. Am J Med Genet B Neuropsychiatr Genet 2003; 117B:97-101. [PMID: 12555243 DOI: 10.1002/ajmg.b.10016] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The methyl-CpG binding protein 2 (MeCP2) gene has recently been identified as the gene responsible for Rett syndrome (RS), a pervasive developmental disorder considered by many to be one of the autism spectrum disorders. Most female patients with MeCP2 mutations exhibit the classic features of RS, including autistic behaviors. Most male patients with MeCP2 mutations exhibit moderate to severe developmental delay/mental retardation. Ninety nine patients from the South Carolina autism project (SCAP) were screened for MeCP2 mutations, including all 41 female patients from whom DNA samples were available plus the 58 male patients with the lowest scores on standard IQ tests and/or the Vineland Adaptive Behavior Scale. No pathogenic mutations were observed in these patients. One patient had the C582T variant, previously reported in the unaffected father of an RS patient. Two other patients had single nucleotide polymorphisms in the 3' UTR of the gene, G1470A and C1516G. These variants were seen in 12/82 and 1/178 phenotypically normal male controls, respectively. The findings from this and other studies suggest that mutations in the coding sequence of the MeCP2 gene are not a significant etiological factor in autism.
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Abstract
Since the initial medical description by Prader, Labhart and Willi in 1956 of individuals with overlapping features, the Prader-Willi syndrome has become recognized as a classical but sporadic genetic syndrome. Prader-Willi syndrome is the most common genetic cause of life-threatening obesity in humans. It is estimated that there are 350,000-400,000 people with this syndrome worldwide. Prader-Willi Syndrome Association USA knows of more than 3,400 persons with Prader-Willi syndrome in the USA out of an approximate 17,000-22,000. Prader-Willi syndrome with an incidence of 1 in 10,000 to 25,000 individuals and Angelman syndrome, an entirely different clinical condition, were the first examples in humans of genetic imprinting. Genetic imprinting or the differential expression of genetic information depending on the parent of origin plays a significant role in other conditions including malignancies.
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Affiliation(s)
- Merlin G Butler
- Children's Mercy Hospitals and Clinics (M.G.B.), Kansas City, Missouri; and John F. Kennedy Center (T.T.), Vanderbilt University, Nashville, Tennessee
| | - Travis Thompson
- Children's Mercy Hospitals and Clinics (M.G.B.), Kansas City, Missouri; and John F. Kennedy Center (T.T.), Vanderbilt University, Nashville, Tennessee
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