Weston T. Powell

The transcription/migration interface in heart precursors of Ciona intestinalis.

Gene regulatory networks direct the progressive determination of cell fate during embryogenesis, but how they control cell behavior during morphogenesis remains largely elusive. Cell sorting, microarrays, and targeted molecular manipulations were used to analyze cardiac cell migration in the ascidian Ciona intestinalis. The heart network regulates genes involved in most cellular activities required for migration, including adhesion, cell polarity, and membrane protrusions. We demonstrated that fibroblast growth factor signaling and the forkhead transcription factor FoxF directly upregulate the small guanosine triphosphatase RhoDF, which synergizes with Cdc42 to contribute to the protrusive activity of migrating cells. Moreover, RhoDF induces membrane protrusions independently of other cellular activities required for migration. We propose that transcription regulation of specific effector genes determines the coordinated deployment of discrete cellular modules underlying migration.

R-loop formation at Snord116 mediates topotecan inhibition of Ube3a-antisense and allele-specific chromatin decondensation

Prader–Willi syndrome (PWS) and Angelman syndrome (AS) are oppositely imprinted autism-spectrum disorders with known genetic bases, but complex epigenetic mechanisms underlie their pathogenesis. The PWS/AS locus on 15q11–q13 is regulated by an imprinting control region that is maternally methylated and silenced. The PWS imprinting control region is the promoter for a one megabase paternal transcript encoding the ubiquitous protein-coding Snrpn gene and multiple neuron-specific noncoding RNAs, including the PWS-related Snord116 repetitive locus of small nucleolar RNAs and host genes, and the antisense transcript to AS-causing ubiquitin ligase encoding Ube3a (Ube3a-ATS). Neuron-specific transcriptional progression through Ube3a-ATS correlates with paternal Ube3a silencing and chromatin decondensation. Interestingly, topoisomerase inhibitors, including topotecan, were recently identified in an unbiased drug screen for compounds that could reverse the silent paternal allele of Ube3a in neurons, but the mechanism of topotecan action on the PWS/AS locus is unknown. Here, we demonstrate that topotecan treatment stabilizes the formation of RNA:DNA hybrids (R loops) at G-skewed repeat elements within paternal Snord116, corresponding to increased chromatin decondensation and inhibition of Ube3a-ATS expression. Neural precursor cells from paternal Snord116 deletion mice exhibit increased Ube3a-ATS levels in differentiated neurons and show a reduced effect of topotecan compared with wild-type neurons. These results demonstrate that the AS candidate drug topotecan acts predominantly through stabilizing R loops and chromatin decondensation at the paternally expressed PWS Snord116 locus. Our study holds promise for targeted therapies to the Snord116 locus for both AS and PWS.

A Prader–Willi locus lncRNA cloud modulates diurnal genes and energy expenditure

Prader–Willi syndrome (PWS), a genetic disorder of obesity, intellectual disability and sleep abnormalities, is caused by loss of non-coding RNAs on paternal chromosome 15q11-q13. The imprinted minimal PWS locus encompasses a long non-coding RNA (lncRNA) transcript processed into multiple SNORD116 small nucleolar RNAs and the spliced exons of the host gene, 116HG. However, both the molecular function and the disease relevance of the spliced lncRNA 116HG are unknown. Here, we show that 116HG forms a subnuclear RNA cloud that co-purifies with the transcriptional activator RBBP5 and active metabolic genes, remains tethered to the site of its transcription and increases in size in post-natal neurons and during sleep. Snord116del mice lacking 116HG exhibited increased energy expenditure corresponding to the dysregulation of diurnally expressed Mtor and circadian genes Clock, Cry1 and Per2. These combined genomic and metabolic analyses demonstrate that 116HG regulates the diurnal energy expenditure of the brain. These novel molecular insights into the energy imbalance in PWS should lead to improved therapies and understanding of lncRNA roles in complex neurodevelopmental and metabolic disorders.

Epigenetic layers and players underlying neurodevelopment

Epigenetic mechanisms convey information above and beyond the sequence of DNA, so it is predicted that they are critical in the complex regulation of brain development and explain the long-lived effects of environmental cues on pre- and early post-natal brain development. Neurons have a complex epigenetic landscape that changes dynamically with transcriptional activity in early life. Here, we summarize progress in our understanding of the discrete layers of the dynamic methylome, chromatin proteome, noncoding RNAs, chromatin loops, and long-range interactions in neuronal development and maturation. Many neurodevelopmental disorders have genetic alterations in these epigenetic modifications or regulators, and these human genetics lessons have demonstrated the importance of these epigenetic players and the epigenetic layers that transcriptional events lay down in the early brain.

Epigenetic mechanisms in diurnal cycles of metabolism and neurodevelopment

The circadian cycle is a genetically encoded clock that drives cellular rhythms of transcription, translation and metabolism. The circadian clock interacts with the diurnal environment that also drives transcription and metabolism during light/dark, sleep/wake, hot/cold and feast/fast daily and seasonal cycles. Epigenetic regulation provides a mechanism for cells to integrate genetic programs with environmental signals in order produce an adaptive and consistent output. Recent studies have revealed that DNA methylation is one epigenetic mechanism that entrains the circadian clock to a diurnal environment. We also review recent circadian findings in the epigenetic neurodevelopmental disorders Prader-Willi, Angelman and Rett syndromes and hypothesize a link between optimal brain development and intact synchrony between circadian and diurnal rhythms.

Probiotic Administration in Infants With Gastroschisis: A Pilot Randomized Placebo-controlled Trial

Objectives: Infants with gastroschisis often require long periods of gastric suctioning and hospitalization. The impact of these interventions on the intestinal microbiota and attempts to alter the microbial community have not been studied. We sought to determine how the intestinal microbiota is influenced by the current treatment of gastroschisis and whether alteration of the intestinal microbiota with a probiotic microbe will influence length of hospitalization. Methods: We performed a randomized, placebo-controlled pilot study of administration of probiotic Bifidobacterium longum subsp. infantis in 24 infants with gastroschisis. The primary outcome was changes in the fecal microbiota, and the secondary outcome was length of hospital stay. Results: Administration of the probiotic or placebo was well tolerated, even during the period of gastric suctioning. The overall microbial communities were not significantly different between groups, although analysis of the final specimens by family demonstrated higher Bifidobacteriaceae, lower Clostridiaceae, and trends toward lower Enterobacteriaceae, Enterococcaceae, Staphylococcaceae, and Streptococcaceae in the probiotic group. Clinical outcomes, including length of hospital stay, did not differ between groups. Conclusions: In this pilot study, there was significant in infants with gastroschisis that was partially attenuated by the administration of B longum subsp. infantis.

Prader–Willi locus Snord116 RNA processing requires an active endogenous allele and neuron-specific splicing by Rbfox3/NeuN

&NA; Prader‐Willi syndrome (PWS), an imprinted neurodevelopmental disorder characterized by metabolic, sleep and neuropsychiatric features, is caused by the loss of paternal SNORD116, containing only non‐coding RNAs (ncRNAs). The primary SNORD116 transcript is processed into small nucleolar RNAs (snoRNAs), which localize to nucleoli, and their spliced host gene 116HG, which is retained at its site of transcription. While functional complementation of the SNORD116 ncRNAs is a desirable goal for treating PWS, the mechanistic requirements of SNORD116 RNA processing are poorly understood. Here we developed and tested a novel transgenic mouse which ubiquitously expresses Snord116 on both a wild‐type and a Snord116 paternal deletion (Snord116+/‐) background. Interestingly, while the Snord116 transgene was ubiquitously expressed in multiple tissues, splicing of the transgene and production of snoRNAs was limited to brain tissues. Knockdown of Rbfox3, encoding neuron‐specific splicing factor neuronal nuclei (NeuN) in Snord116+/‐‐derived neurons, reduced splicing of the transgene in neurons. RNA fluorescence in situ hybridization for 116HG revealed a single significantly larger signal in transgenic mice, demonstrating colocalization of transgenic and endogenous 116HG RNAs. Similarly, significantly increased snoRNA levels were detected in transgenic neuronal nucleoli, indicating that transgenic Snord116 snoRNAs were effectively processed and localized. In contrast, neither transgenic 116HG nor snoRNAs were detectable in either non‐neuronal tissues or Snord116+/‐ neurons. Together, these results demonstrate that exogenous expression and neuron‐specific splicing of the Snord116 locus are insufficient to rescue the genetic deficiency of Snord116 paternal deletion. Elucidating the mechanisms regulating Snord116 processing and localization is essential to develop effective gene replacement therapies for PWS.

Use of complex oligonucleotide libraries for concurrent high-resolution fluorescence imaging of both DNA and RNA in various sample types

Fluorescence in situ Hybridization (FISH) is a powerful technique for determining the localization specific nucleic acid sequences within individual cells. Previously, the use of FISH has often been dependent upon access to cloned template DNA for the generation of probes, which can be difficult if clones for specific regions are unavailable, or if the genomic region of interest contains repetitive and/or other problematic sequences. We have developed the ability to chemically synthesize DNA in massively parallel reactions, which we have used to produce libraries of oligonucleotides up to 200 bases in length that can be utilized for the generation of FISH probes. The sequences of the oligonucleotides in these libraries are selected in silico using empirically determined criteria so as to avoid repetitive elements or regions homologous to other non-targeted loci. We have found that these oligonucleotide library-derived FISH probes can detect human genomic regions as small as 1.8 kb and as large as whole chromosomes in both metaphase and interphase cells, using the same simple assay protocol. Because of the inherent flexibility in our probe design methods, we can readily visualize regions rich in repeats and/or GC content. We have also used these oligonucleotide library-derived FISH probes to detect the localization of a variety of both coding and non-coding RNAs in fixed tissue culture cells and formalin-fixed paraffin-embedded tissue sections, using both conventional fluorescence and structured illumination microscopy. Simultaneous hybridization of FISH probes labeled with different fluorophores enables visualization of multiple sequences at once. Using probes designed specifically to transcribed vs. non-transcribed regions has enabled the simultaneously detect DNA and RNA from the same locus, or from two different loci, in the same FISH assay. The ability to generate high performance FISH probes using chemically synthesized oligo libraries that can simultaneously detect DNA and RNA yields a valuable tool for studies of how localization of specific nucleic acids impacts biological function.

Imprinting in the CNS and Neurodevelopmental Disorders

Genomic imprinting is allele-specific silencing based on maternal or paternal inheritance via epigenetic mechanisms. All imprinted loci express a long non-coding RNA (lncRNA) in an allele-specific manner dependent on a differentially methylated region (DMR). We describe the general mechanisms of genomic imprinting during development, focusing on how lncRNA serve to translate the stable epigenetic mark of DNA methylation in order to allow for tissue specific patterns of imprinted gene expression. Disruption of an lncRNA encoded on chromosome 15q11-q13 plays a central role in the pathogenesis of the neurodevelopmental disorders Prader–Willi syndrome and Angelman syndrome, and regulation of gene expression throughout 15q11-q13 is important in brain development. We focus on 15q11-q13 as a model example for the role genomic imprinting plays in human brain development, and discuss the role other imprinted loci may play in brain development.

Abstract 4205: Simultaneous high resolution fluorescence imaging of cellular DNA and RNA enabled by complex oligonucleotide libraries in various sample types.

Proceedings: AACR 104th Annual Meeting 2013; Apr 6-10, 2013; Washington, DC Fluorescence in situ Hybridization (FISH) is a powerful technique for determining the structure, organization, and localization of specific nucleic acid sequences within individual cells. However, the use of FISH has often been dependent upon access to cloned template DNA for the generation of probes, which can be difficult if clones for specific regions are unavailable, or if the genomic region of interest contains repetitive and/or other problematic sequences. We have leveraged our ability to chemically synthesize DNA in massively parallel reactions to produce libraries of oligonucleotides up to 200 bases in length that can be used for the generation of FISH probes. The sequences of the oligonucleotides in these libraries are selected in silico using empirically determined criteria so as to avoid repetitive elements or regions homologous to other non-targeted loci. Using oligonucleotide library-derived FISH probes on DNA, human genomic regions as small as 1.8 kb and as large as whole chromosomes can be visualized in both metaphase and interphase cells using the same simple assay protocol. Because of the inherent flexibility in our probe design methods, we readily visualized regions rich in repeats and/or GC content. We have also used these oligonucleotide library-derived FISH probes to detect the localization of a variety of both coding and non-coding RNAs in fixed cells, using both conventional fluorescence and structured illumination microscopy. Simultaneous hybridization of FISH probes labeled with different fluorophores enables visualization of multiple sequences at once. Using probes designed specifically to transcribed vs. non-transcribed regions, we have been able to simultaneously detect DNA and RNA from the same locus in the same FISH assay. We have successfully used this technique in several types of fixed tissue culture cells as well as in formalin-fixed paraffin-embedded tissue sections. Our oligo FISH methods are readily compatible with the co-detection of cellular proteins by immunocytochemistry. The ability to generate high performance FISH probes using chemically synthesized oligo libraries that can work flexibly with co-detection of other molecules yields a valuable tool for studies of how localization of specific nucleic acids impacts biological function. Citation Format: Robert A. Ach, Peter Tsang, Alicia Scheffer-Wong, Laurakay Bruhn, Weston Powell, Janine LaSalle, Alice Yamada. Simultaneous high resolution fluorescence imaging of cellular DNA and RNA enabled by complex oligonucleotide libraries in various sample types. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4205. doi:10.1158/1538-7445.AM2013-4205