Multiple Epigenetic Modifiers Induce Aggressive Viral Extinction in Extraembryonic Endoderm Stem Cells

Department of Obstetrics & Gynecology, University of Western Ontario, Schulich School of Medicine and Dentistry, London, Ontario N6A 4V2, Canada.
Cell stem cell (Impact Factor: 22.27). 05/2010; 6(5):457-67. DOI: 10.1016/j.stem.2010.03.014
Source: PubMed


To prevent insertional mutagenesis arising from retroviral reactivation, cells of embryonic origin possess a unique capacity to silence retroviruses. Given the distinct modes of X chromosome inactivation between embryonic and extraembryonic lineages, we investigated paradigms of viral extinction. We show that trophectoderm stem cells do not silence retroviral transcription, whereas extraembryonic endoderm stem cells aggressively extinguish proviral transcription, even more rapidly than do embryonic stem cells. By using a short hairpin RNA library, we identified epigenetic modifiers of retroviral extinction in extraembryonic endoderm stem cells. Multiple chromatin remodeling and polycomb repressor complex proteins act to modulate integrated, as well as endogenous, retroviral element silencing, with a subset of factors displaying differential effects between stem cell types. Furthermore, our data suggest that small RNAs play a role in this process through interactions with the Argonaute family. Our results further the understanding of mechanisms regulating retroviral transcription in different stem cell lineages.

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    • "These experiments revealed significant declines in the levels of H3K27 Me3 for all transposable element families examined, suggesting the global distribution of this mark had become altered as a consequence of in vitro EtOH exposure (Fig. 3A). Given the observed role of Polycomb group complexes and by proxy, H3K27 Me3 in maintaining the repressed state of transposable elements (Golding et al., 2010), we had anticipated a reduction in this mark would be correlated with a proportional increase in LINE1, IAP, MusD, and Etn transcription. Surprisingly, only the LINE1 family and 60 mg/dl IAP group displayed statistically significant changes (p = 0.001 and p = 0.002, respectively) and transcript levels for both of these transposable elements were decreased (Fig. 3B). "
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    ABSTRACT: From studies using a diverse range of model organisms, we now acknowledge that epigenetic changes to chromatin structure provide a plausible link between environmental teratogens and alterations in gene expression leading to disease. Observations from a number of independent laboratories indicate that ethanol (EtOH) has the capacity to act as a powerful epigenetic disruptor and potentially derail the coordinated processes of cellular differentiation. In this study, we sought to examine whether primary neurospheres cultured under conditions maintaining stemness were susceptible to alcohol-induced alterations in the histone code. We focused our studies on trimethylated histone 3 lysine 4 and trimethylated histone 3 lysine 27, as these are 2 of the most prominent posttranslational histone modifications regulating stem cell maintenance and neural differentiation. Primary neurosphere cultures were maintained under conditions promoting the stem cell state and treated with EtOH for 5 days. Control and EtOH-treated cellular extracts were examined using a combination of quantitative RT-PCR and chromatin immunoprecipitation techniques. We find that the regulatory regions of genes controlling both neural precursor cell identity and processes of differentiation exhibited significant declines in the enrichment of the chromatin marks examined. Despite these widespread changes in chromatin structure, only a small subset of genes including Dlx2, Fabp7, Nestin, Olig2, and Pax6 displayed EtOH-induced alterations in transcription. Unexpectedly, the majority of chromatin-modifying enzymes examined including members of the Polycomb Repressive Complex displayed minimal changes in expression and localization. Only transcripts encoding Dnmt1, Uhrf1, Ehmt1, Ash2 l, Wdr5, and Kdm1b exhibited significant differences. Our results indicate that primary neurospheres maintained as stem cells in vitro are susceptible to alcohol-induced perturbation of the histone code and errors in the epigenetic program. These observations indicate that alterations to chromatin structure may represent a crucial component of alcohol teratogenesis and progress toward a better understanding of the developmental origins of fetal alcohol spectrum disorders.
    Alcoholism Clinical and Experimental Research 03/2013; 37(7). DOI:10.1111/acer.12080 · 3.21 Impact Factor
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    • "Previous studies in our laboratory have utilized stem cell lines derived from Mus musculus castaneus × Mus musculus (C57Black6) F1 embryos (Golding et al., 2010, 2011. Polymorphisms between these genetic strains allow the examination of mono-allelic patterns of epigenetic marks and gene expression within loci regulated by genomic imprinting (Golding et al., 2010). ES cultures were maintained in DMEM ( "
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    ABSTRACT: Identification of the transcriptional networks disrupted by prenatal ethanol exposure remains a core requirement to better understanding the molecular mechanisms of alcohol-induced teratogenesis. In this regard, quantitative reverse-transcriptase polymerase chain reaction (qPCR) has emerged as an essential technique in our efforts to characterize alterations in gene expression brought on by exposure to alcohol. However, many publications continue to report the utilization of inappropriate methods of qPCR normalization, and for many in vitro models, no consistent set of empirically tested normalization controls have been identified. In the present study, we sought to identify a group of candidate reference genes for use within studies of alcohol exposed embryonic, placental, and neurosphere stem cells under both conditions maintaining stemness as well as throughout in vitro differentiation. To this end, we surveyed the recent literature and compiled a short list of fourteen candidate genes commonly used as normalization controls in qPCR studies of gene expression. This list included: Actb, B2m, Gapdh, Gusb, H2afz, Hk2, Hmbs, Hprt, Mrpl1, Pgk1, Ppia, Sdha, Tbp, and Ywhaz. From these studies, we find no single candidate gene was consistently refractory to the influence of alcohol nor completely stable throughout in vitro differentiation. Accordingly, we propose normalizing qPCR measurements to the geometric mean C(T) values obtained for three independent reference mRNAs as a reliable method to accurately interpret qPCR data and assess alterations in gene expression within alcohol treated cultures. Highlighting the importance of careful and empirical reference gene selection, the commonly used reference gene Actb was often amongst the least stable candidate genes tested. In fact, it would not serve as a valid normalization control in many cases. Data presented here will aid in the design of future experiments using stem cells to study the transcriptional processes driving differentiation, and model the developmental impact of teratogens.
    Alcohol (Fayetteville, N.Y.) 01/2013; 47(2). DOI:10.1016/j.alcohol.2012.12.003 · 2.01 Impact Factor
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    • "Presumptive zygotes were placed in a 100 mM sucrose solution in M199 Hanks Hepes media (Invitrogen) during micromanipulation. Recombinant lentivirus was produced as described above (Miyoshi et al., 1998; Golding et al., 2010), and viral supernatant was ultracentrifuged prior to microinjection to increase titer. Only concentrated virus with a titer at or above 1 Â 10 9 IU/ml was used for microinjection of embryos. "
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    ABSTRACT: Myostatin (MSTN) is a well-known negative regulator of muscle growth. Animals that possess mutations within this gene display an enhanced muscling phenotype, a desirable agricultural trait. Increased neonatal morbidity is common, however, resulting from complications arising from the birth of offspring with increased fetal muscle mass. The objective of the current research was to generate an attenuated MSTN-null phenotype in a large-animal model using RNA interference to enhance muscle development without the detrimental consequences of an inactivating mutation. To this end, we identified a series of short interfering RNAs that demonstrated effective suppression of MSTN mRNA and protein levels. To produce transgenic offspring capable of stable MSTN suppression in vivo, a recombinant lentiviral vector expressing a short hairpin RNA (shRNA) targeting MSTN for silencing was introduced into bovine fetal fibroblasts. These cells were used as nucleus donors for somatic cell nuclear transfer (SCNT). Twenty blastocysts were transferred into seven recipient cows resulting in five pregnancies. One transgenic calf developed to term, but died following delivery by Caesarean-section. As an alternative strategy, microinjection of recombinant lentiviral particles into the perivitelline space of in vitro-produced bovine zygotes was utilized to produce 40 transgenic blastocysts that were transferred into 14 recipient cows, resulting in 7 pregnancies. Five transgenic calves were produced, of which three expressed the transgene. This is the first report of transgenic livestock produced by direct injection of a recombinant lentivirus, and expressing transgenes encoding shRNAs targeting an endogenous gene (myostatin) for silencing.
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