Most cases of Angelman syndrome (AS) result from loss or inactivation of ubiquitin protein ligase 3A (UBE3A), a gene displaying maternal-specific expression in brain. Epigenetic silencing of the paternal UBE3A allele in brain appears to be mediated by a non-coding UBE3A antisense (UBE3A-ATS). In human, UBE3A-ATS extends approximately 450 kb to UBE3A from the small nuclear ribonucleoprotein N (SNURF/SNRPN) promoter region that contains a cis-acting imprinting center (IC). The concept of a single large antisense transcript is difficult to reconcile with the observation that SNURF/SNRPN shows a ubiquitous pattern of expression while the more distal part of UBE3A-ATS, which overlaps UBE3A, is brain specific. To address this problem, we examined murine transcripts initiating from several alternative exons dispersed within a 500 kb region upstream of Snurf/Snrpn. Similar to Ube3a-ATS, these upstream (U) exon-containing transcripts are expressed at neuronal stages of differentiation in a cell culture model of neurogenesis. These findings suggest the novel hypothesis that brain-specific transcription of Ube3a-ATS is regulated by the U exons rather than Snurf/Snrpn exon 1 as previously suggested from human studies. In support of this hypothesis, we describe U-Ube3a-ATS transcripts where U exons are spliced to Ube3a-ATS with the exclusion of Snurf-Snrpn. We also show that the murine U exons have arisen by genomic duplication of segments that include elements of the IC, suggesting that the brain specific silencing of Ube3a is due to multiple alternatively spliced IC-Ube3a-ATS transcripts.

Hyperactivation of p53 leads to a reduction in tumor formation and an unexpected shortening of life span in two different model systems . The decreased life span occurs with signs of accelerated aging, such as osteoporosis, reduction in body weight, atrophy of organs, decreased stress resistance, and depletion of hematopoietic stem cells. These observations suggest a role for p53 in the determination of life span and the speculation that decreasing p53 activity may result in positive effects on some aging phenotypes . In this report, we show that expression of dominant-negative versions of Drosophila melanogaster p53 in adult neurons extends life span and increases genotoxic stress resistance in the fly. Consistent with this, a naturally occurring allele with decreased p53 activity has been associated with extended survival in humans . Expression of the dominant-negative Drosophila melanogaster p53 constructs does not further increase the extended life span of flies that are calorie restricted, suggesting that a decrease in p53 activity may mediate a component of the calorie-restriction life span-extending pathway in flies.

Prader-Willi syndrome (PWS) is a complex neurogenetic disorder. The phenotype is likely to be a contiguous gene syndrome involving genes which are paternally expressed only, located in the human 15q11-q13 region. Four mouse models of PWS have been reported but these do not definitively allow the delineation of the critical region and the associated genes involved in the aetiology of PWS. Moreover, targeted mutagenesis of mouse homologues of the human candidate PWS genes does not appear to result in any of the features of PWS. Therefore, the isolation of new genes in this region remains crucial for a better understanding of the molecular basis of PWS. In this manuscript, we report the characterization of MAGEL2 and its mouse homologue Magel2. These are located in the human 15q11-q13 and mouse 7C regions, in close proximity to NDN / Ndn. By northern blot analysis we did not detect any expression of MAGEL2 / Magel2 but by RT-PCR analysis, specific expression was detected in fetal and adult brain and in placenta. Both genes are intronless with tandem direct repeat sequences contained within a CpG island in the 5'-untranscribed region. The transcripts encode putative proteins that are homologous to the MAGE proteins and NDN. Moreover, MAGEL2 / Magel2 are expressed only from the paternal allele in brain, suggesting a potential role in the aetiology of PWS and its mouse model, respectively.

BackgroundDuplications of the chromosome 15q11-q13.1 region are associated with an estimated 1 to 3% of all autism cases, making this copy number variation (CNV) one of the most frequent chromosome abnormalities associated with autism spectrum disorder (ASD). Several genes located within the 15q11-q13.1 duplication region including ubiquitin protein ligase E3A (UBE3A), the gene disrupted in Angelman syndrome (AS), are involved in neural function and may play important roles in the neurobehavioral phenotypes associated with chromosome 15q11-q13.1 duplication (Dup15q) syndrome.MethodsWe have generated induced pluripotent stem cell (iPSC) lines from five different individuals containing CNVs of 15q11-q13.1. The iPSC lines were differentiated into mature, functional neurons. Gene expression across the 15q11-q13.1 locus was compared among the five iPSC lines and corresponding iPSC-derived neurons using quantitative reverse transcription PCR (qRT-PCR). Genome-wide gene expression was compared between neurons derived from three iPSC lines using mRNA-Seq.ResultsAnalysis of 15q11-q13.1 gene expression in neurons derived from Dup15q iPSCs reveals that gene copy number does not consistently predict expression levels in cells with interstitial duplications of 15q11-q13.1. mRNA-Seq experiments show that there is substantial overlap in the genes differentially expressed between 15q11-q13.1 deletion and duplication neurons, Finally, we demonstrate that UBE3A transcripts can be pharmacologically rescued to normal levels in iPSC-derived neurons with a 15q11-q13.1 duplication.ConclusionsChromatin structure may influence gene expression across the 15q11-q13.1 region in neurons. Genome-wide analyses suggest that common neuronal pathways may be disrupted in both the Angelman and Dup15q syndromes. These data demonstrate that our disease-specific stem cell models provide a new tool to decipher the underlying cellular and genetic disease mechanisms of ASD and may also offer a pathway to novel therapeutic intervention in Dup15q syndrome.

Prader-Willi syndrome (PWS) and Angelman syndrome (AS) are two neurodevelopmental disorders most often caused by deletions of the same region of paternally inherited and maternally inherited human chromosome 15q, respectively. AS is a single gene disorder, caused by the loss of function of the ubiquitin ligase E3A (UBE3A) gene, while PWS is still considered a contiguous gene disorder. Rare individuals with PWS who carry atypical microdeletions on chromosome 15q have narrowed the critical region for this disorder to a 108 kb region that includes the SNORD116 snoRNA cluster and the Imprinted in Prader-Willi (IPW) non-coding RNA. Here we report the derivation of induced pluripotent stem cells (iPSCs) from a PWS patient with an atypical microdeletion that spans the PWS critical region. We show that these iPSCs express brain-specific portions of the transcripts driven by the PWS imprinting center, including the UBE3A antisense transcript (UBE3A-ATS). Furthermore, UBE3A expression is imprinted in most of these iPSCs. These data suggest that UBE3A imprinting in neurons only requires UBE3A-ATS expression, and no other neuron-specific factors. These data also suggest that a boundary element lying within the PWS critical region prevents UBE3A-ATS expression in non-neural tissues.