|ognizant Communication Corporation|
VOLUME 14, NUMBER 3
Gene Expression, Vol. 14, pp. 131-147
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Mammalian Rrn3 Is Required for the Formation of a Transcription Competent Preinitiation Complex Containing RNA Polymerase I
Alice H. Cavanaugh,1 Ann Evans,1 and Lawrence I. Rothblum2
1Sigfried and Janet Weis Center for Research, Geisinger Clinic,
Danville, PA, USA
2Department of Cell Biology, The University of Oklahoma College of Medicine, Oklahoma City, OK, USA
Mammalian Rrn3, an essential, polymerase-associated protein, is inactivated when cells are treated with cycloheximide, resulting in the inhibition of transcription by RNA polymerase I. Although Rrn3 is essential for transcription, its function in rDNA transcription has not been determined. For example, it is unclear whether Rrn3 is required for initiation or elongation by RNA polymerase I. Rrn3 has been shown to interact with the 43-kDa subunit of RNA polymerase I and with two of the subunits of SL1. In the current model for transcription, Rrn3 functions to recruit RNA polymerase I to the committed complex formed by SL1 and the rDNA promoter. To examine the question as to whether Rrn3 is required for the recruitment of RNA polymerase I to the template, we developed a novel assay similar to chromatin immunoprecipitation assays. We found that RNA polymerase I can be recruited to a template in the absence of active Rrn3. However, that complex will not initiate transcription, even after Rrn3 is added to the reaction. Interestingly, the complex that forms in the presence of active Rrn3 is biochemically distinguishable from that which forms in the absence of active Rrn3. For example, the functional complex is fivefold more resistant to heparin than that which forms in the absence of Rrn3. Our data demonstrate that Rrn3 must be present when the committed template complex is forming for transcription to occur.
Key words: Rrn3; RNA polymerase I; Transcription initiation
Address correspondence to Lawrence I. Rothblum, Department of Cell Biology, The University of Oklahoma College of Medicine, 940 Stanton L. Young, BMSB 553C, Oklahoma City, OK 73104, USA. Tel: 405-271-2377; E-mail: lrothblu@OUHSC.edu
Effects of Atherogenic Diet and Atorvastatin Treatment on Gene Expression Profiles in the C57BL/6J Mouse Liver
Yulan Zhao,* Mei-Yen Chan,* Shuli Zhou, and Chew-Kiat Heng
Department of Paediatrics, Yong Loo Lin School of Medicine, National University of Singapore, Singapore
This study investigated the early and long-term effects of atherogenic diet on hepatic gene expression, and the restorative effects of atorvastatin in treating hypercholesterolemia. Two groups of female C57BL/6J mice were fed standard chow or atherogenic diet for 1-week early phase study and two other groups for 10 weeks. The fifth group had daily 10 mg/kg atorvastatin injections for 3 weeks from week 8 of the atherogenic diet. Gene expression profiling was carried out with Affymetrix GeneChips. One-week atherogenic diet elevated 38 and inhibited 127 gene expressions, while 10-week atherogenic diet elevated 165 and inhibited 281 genes by more than twofold. Atorvastatin could restore 78.2% and 68%, respectively, of the genes to normal levels. Genes in the Insig (insulin-induced gene)-SREBP (sterol regulatory element binding proteins) pathway were mostly inhibited by atherogenic diet at week 1 but elevated at week 10. Of these, 65.2% were restored by atorvastatin. In conclusion, lipid homeostatic mechanism coped well with short-term atherogenic diet. However, when such a diet was prolonged, the mechanism was no longer effective but entered into a pathological state in which lipogenic genes, especially those in the Insig-SREBP pathway, were upregulated. Atorvastatin could restore changes in the Insig-SREBP pathway that were induced by the atherogenic diet.
Key words: Atherogenic diet; Statin; Microarray; Insig-SREBP pathway
Address correspondence to Chew-Kiat Heng, Ph.D., Department of Paediatrics, Yong Loo Lin School of Medicine, National University of Singapore, Singapore 119074. Tel: (65)67725708; Fax: (65)67742796; E-mail: email@example.com
*Both authors contributed equally.
Ethanol Exposure During Neurogenesis Induces Persistent Effects on Neural Maturation: Evidence From an Ex Vivo Model of Fetal Cerebral Cortical Neuroepithelial Progenitor Maturation
Cynthia Camarillo1 and Rajesh C. Miranda1,2
1Department of Neuroscience and Experimental Therapeutics,
Texas A&M Health Science Center College of Medicine, College Station,
2Center for Environmental and Rural Health, Texas A&M University, College Station, TX, USA
Ethanol is a significant neuroteratogen. We previously used fetal cortical-derived neurosphere cultures as an ex vivo model of the second trimester ventricular neuroepithelium, and showed that ethanol directly induced fetal stem and progenitor cell proliferation and maturation without inducing death. However, ethanol is defined as a teratogen because of its capacity to persistently disrupt neural maturation beyond a specific exposure period. We therefore utilized a simplified neuronal maturation paradigm to examine the immediate and persistent changes in neuronal migration following ethanol exposure during the phase of neuroepithelial proliferation. Our data indicate that mRNA transcripts for migration-associated genes RhoA, Paxillin (Pxn), and CDC42 were immediately induced following ethanol exposure, whereas dynein light chain, LC8-type 1 (DYNLL1), and growth-associated protein (Gap)-43 were suppressed. With the exception of Gap43, ethanol did not induce persistent changes in the other mRNAs, suggesting that ethanol had an activational, rather than organizational, impact on migration-associated mRNAs. However, despite this lack of persistent effects on these mRNAs, ethanol exposure during the proliferation period significantly increased subsequent neuronal migration. Moreover, differentiating neurons, pretreated with ethanol during the proliferation phase, exhibited reduced neurite branching and an increased length of primary neurites, indicating a persistent destabilization of neuronal maturation. Collectively, our data indicate that ethanol-exposed proliferating neuroepithelial precursors exhibit subsequent differentiation-associated increases in migratory behavior, independent of mRNA transcript levels. These data help explain the increased incidence of cerebral cortical neuronal heterotopias associated with the fetal alcohol syndrome.
Key words: Fetal alcohol syndrome; Neural stem cells; Gap43; RhoA; Paxillin; CDC42; Dynein light chain; LC8-type 1 (DYNLL1); Migration
Address correspondence to Rajesh C. Miranda, Department of Neuroscience and Experimental Therapeutics, Texas A&M Health Science Center College of Medicine, College Station, TX 77843, USA. Tel: 979-862-3418; E-mail: firstname.lastname@example.org
Methylation-Mediated Downregulation of the B-Cell Translocation Gene 3 (BTG3) in Breast Cancer Cells
Jingwei Yu,1 Yingsha Zhang,1 Zhongxia Qi,2 Daniel Kurtycz,2 Guido Vacano,3 and David Patterson3
1Department of Laboratory Medicine, University of California,
San Francisco, San Francisco, CA, USA
2Department of Pathology and Laboratory Medicine, University of Wisconsin-Madison, Madison, WI, USA
3Eleanor Roosevelt Institute and Department of Biological Sciences, University of Denver, Denver, CO, USA
The incidence of solid tumors is low in individuals with Down syndrome (trisomy 21), suggesting the presence of one or more tumor suppressor genes on chromosome 21. Consistent with this finding, previous work has demonstrated frequent loss of heterozygosity (LOH) of a small (<5 Mb) region of chromosome 21, particularly in breast cancer, indicating that a tumor suppressor gene(s) may be located in this region. We investigated the expression of BTG3, a gene in the LOH region on chromosome 21, in breast cancer cell lines. BTG3 has been shown to be a negative regulator of SRC tyrosine kinase, and BTG3 is a target of p53 and inhibits the activity of the E2F1 transcription factor. Here we demonstrate that in a wide variety of human breast cancer cell lines, BTG3 expression is markedly reduced in the absence of detectable mutations in the BTG3 promoter and coding region. In these cell lines, the promoter region of the BTG3 gene is hypermethylated when compared to normal breast cell lines. BTG3 gene expression can be restored by treatment with 5´-aza-deoxycytidine, an inhibitor of DNA methylation. These data support the hypothesis that BTG3 may act to suppress tumorigenesis and that hypermethylation is an important mechanism for inactivation of BTG3 and perhaps other tumor suppressor genes. The findings are consistent with a role for an additional copy of BTG3 in the reduced incidence of breast cancer in individuals with Down syndrome.
Key words: BTG3; DNA methylation; Breast cancer; Tumor suppressor gene
Address correspondence to Jingwei Yu, Department of Laboratory Medicine, University of California, San Francisco, 185 Berry Street, Suite 290, San Francisco, CA 94107, USA. Tel: +01-415-353-4809; Fax: +01-415-353-4877; E-mail: Jingwei.Yu@ucsfmedctr.org
Even Neural Stem Cells Get the Blues: Evidence for a Molecular Link Between Modulation of Adult Neurogenesis and Depression
Rosanne M. Thomas1 and Daniel A. Peterson2
1Department of Physical Therapy, College of Health Professions,
Rosalind Franklin University of Medicine and Science, North Chicago, IL,
2Neural Repair and Neurogenesis Laboratory, Center for Stem Cell and Regenerative Medicine, Rosalind Franklin University of Medicine and Science, North Chicago, IL, USA
An emerging hypothesis, linking modulation of neurogenesis with the onset and subsequent treatment of depression, has received much attention recently as an attractive explanation for successful behavioral changes induced by antidepressant medication in both humans and animals. However, evidence for such a link remains elusive and inconsistent. This review discusses evidence for modulation of neurogenesis as a neurobiological substrate for depression within the context of heterogeneous animal models of depression. Examining the evidence currently available linking neurogenesis and depression is problematic for at least four reasons: 1) approaches to document ongoing neurogenesis and neuronal lineage commitment are varied, making cross-study comparison difficult; 2) as the functional contribution of adult neurogenesis has yet to be completely determined, it is speculative to state a functional significance to changes in neurogenesis; 3) there is diversity in animal models of depression with variable degrees of correlation with human depression; and 4) there remains insufficient knowledge of molecular factors and changes in gene expression that conclusively link neurogenesis modulation and depression. This review examines the current state of evidence regarding the following: 1) consistent data collection delineating the existence of neurogenesis, its stages of progression, and stage modulation; 2) the functional contribution of adult hippocampal neurogenesis and the use of stress-based animal models for its modulation, 3) possible molecular links between antidepressant medication and neurogenesis, specifically neurotrophins and trophic factors; and finally 4) specific suggestions for further investigations necessary to warrant full acceptance of a link between modulation of neurogenesis and depression.
Key words: Stress; Hippocampus; Dentate gyrus; BDNF; Antidepressants; BrdU
Address correspondence to Daniel A. Peterson, Neural Repair and Neurogenesis
Laboratory, Center for Stem Cell and Regenerative Medicine, Rosalind Franklin
University of Medicine and Science, 3333 Green Bay Road, North Chicago,
IL 60064, USA. Tel: 847-578-3411; Fax: 847-578-8545; E-mail: email@example.com