Life Sciences Commons^™

Evolution Acts On Enhancer Organization To Fine-Tune Gradient Threshold Readouts, Justin Crocker, Yoichiro Tamori, Albert Erives

Dartmouth Scholarship

The elucidation of principles governing evolution of gene regulatory sequence is critical to the study of metazoan diversification. We are therefore exploring the structure and organizational constraints of regulatory sequences by studying functionally equivalent cis-regulatory modules (CRMs) that have been evolving in parallel across several loci. Such an independent dataset allows a multi-locus study that is not hampered by nonfunctional or constrained homology. The neurogenic ectoderm enhancers (NEEs) of Drosophila melanogaster are one such class of coordinately regulated CRMs. The NEEs share a common organization of binding sites and as a set would be useful to study the relationship …

Identification Of Two Gene Clusters And A Transcriptional Regulator Required For Pseudomonas Aeruginosa Glycine Betaine Catabolism, Matthew J. Wargo, Benjamin S. Szwergold, Deborah A. Hogan

Dartmouth Scholarship

Glycine betaine (GB), which occurs freely in the environment and is an intermediate in the catabolism of choline and carnitine, can serve as a sole source of carbon or nitrogen in Pseudomonas aeruginosa. Twelve mutants defective in growth on GB as the sole carbon source were identified through a genetic screen of a nonredundant PA14 transposon mutant library. Further growth experiments showed that strains with mutations in two genes, gbcA (PA5410) and gbcB (PA5411), were capable of growth on dimethylglycine (DMG), a catabolic product of GB, but not on GB itself. Subsequent nuclear magnetic resonance (NMR) experiments with 1,2-(13)C-labeled choline …

Ovarian Development In Mice Requires The Gata4-Fog2 Transcription Complex, Nikolay L. Manuylov, Fatima O. Smagulova, Lyndsay Leach, Sergei G. Tevosian

Dartmouth Scholarship

We have demonstrated previously that mammalian sexual differentiation requires both the GATA4 and FOG2 transcriptional regulators to assemble the functioning testis. Here we have determined that the sexual development of female mice is profoundly affected by the loss of GATA4-FOG2 interaction. We have also identified the Dkk1 gene, which encodes a secreted inhibitor of canonical beta-catenin signaling, as a target of GATA4-FOG2 repression in the developing ovary. The tissue-specific ablation of the beta-catenin gene in the gonads disrupts female development. In Gata4(ki/ki); Dkk1(-/-) or Fog2(-/-); Dkk1(-/-) embryos, the normal ovarian gene expression pattern is partially restored. Control of ovarian development …

Evolution Of The Holozoan Ribosome Biogenesis Regulon, Seth J. Brown, Michael D. Cole, Albert J. Erives

Dartmouth Scholarship

The ribosome biogenesis (RiBi) genes encode a highly-conserved eukaryotic set of nucleolar proteins involved in rRNA transcription, assembly, processing, and export from the nucleus. While the mode of regulation of this suite of genes has been studied in the yeast, Saccharomyces cerevisiae, how this gene set is coordinately regulated in the larger and more complex metazoan genomes is not understood. Here we present genome-wide analyses indicating that a distinct mode of RiBi regulation co-evolved with the E(CG)-binding, Myc:Max bHLH heterodimer complex in a stem-holozoan, the ancestor of both Metazoa and Choanoflagellata, the protozoan group most closely related to animals. These …

Metabolic Engineering Of A Thermophilic Bacterium To Produce Ethanol At High Yield, A. Joe Shaw, Kara K. Podkaminer, Sunil G. Desai, John S. Bardsley, Stephen R. Rogers, Philip G. Thorne, David A. Hogsett, Lee R. Lynd

Dartmouth Scholarship

We report engineering Thermoanaerobacterium saccharolyticum, a thermophilic anaerobic bacterium that ferments xylan and biomass-derived sugars, to produce ethanol at high yield. Knockout of genes involved in organic acid formation (acetate kinase, phosphate acetyltransferase, and L-lactate dehydrogenase) resulted in a strain able to produce ethanol as the only detectable organic product and substantial changes in electron flow relative to the wild type. Ethanol formation in the engineered strain (ALK2) utilizes pyruvate:ferredoxin oxidoreductase with electrons transferred from ferredoxin to NAD(P), a pathway different from that in previously described microbes with a homoethanol fermentation. The homoethanologenic phenotype was stable for >150 generations …

The Bile Response Repressor Brer Regulates Expression Of The Vibrio Cholerae Breab Efflux System Operon, Francisca A. Cerda-Maira, Carol S. Ringelberg, Ronald K. Taylor

Dartmouth Scholarship

Enteric pathogens have developed several resistance mechanisms to survive the antimicrobial action of bile. We investigated the transcriptional profile of Vibrio cholerae O1 El Tor strain C6706 under virulence gene-inducing conditions in the presence and absence of bile. Microarray analysis revealed that the expression of 119 genes was affected by bile. The mRNA levels of genes encoding proteins involved in transport were increased in the presence of bile, whereas the mRNA levels of genes encoding proteins involved in pathogenesis and chemotaxis were decreased. This study identified genes encoding transcriptional regulators from the TetR family (vexR and breR) and …

Integration Host Factor Positively Regulates Virulence Gene Expression In Vibrio Cholerae, Emily Stonehouse, Gabriela Kovacikova, Ronald K. Taylor, Karen Skorupski

Dartmouth Scholarship

Virulence gene expression in Vibrio cholerae is dependent upon a complex transcriptional cascade that is influenced by both specific and global regulators in response to environmental stimuli. Here, we report that the global regulator integration host factor (IHF) positively affects virulence gene expression in V. cholerae. Inactivation of ihfA and ihfB, the genes encoding the IHF subunits, decreased the expression levels of the two main virulence factors tcpA and ctx and prevented toxin-coregulated pilus and cholera toxin production. IHF was found to directly bind to and bend the tcpA promoter region at an IHF consensus site centered at position 162 …

Minimal Components Of The Rna Polymerase Ii Transcription Apparatus Determine The Consensus Tata Box, Gudrun Bjornsdottir, Lawrence C. Myers

Dartmouth Scholarship

In Saccharomyces cerevisiae, multiple approaches have arrived at a consensus TATA box sequence of TATA(T/A)A(A/T)(A/G). TATA-binding protein (TBP) affinity alone does not determine TATA box function. To discover how a minimal set of factors required for basal and activated transcription contributed to the sequence requirements for a functional TATA box, we performed transcription reactions using highly purified proteins and CYC1 promoter TATA box mutants. The TATA box consensus sequence is a good predictor of promoter activity. However, several nonconsensus sequences are almost fully functional, indicating that mechanistic requirements are not the only selective pressure on the TATA box. We …

The Mads-Domain Transcriptional Regulator Agamous-Like15 Promotes Somatic Embryo Development In Arabidopsis And Soybean, Dhiraj Thakare, Weining Tang, Kristine Hill, Sharyn E. Perry

Dartmouth Scholarship

The MADS-domain transcriptional regulator AGAMOUS-LIKE15 (AGL15) has been reported to enhance somatic embryo development when constitutively expressed. Here we report that loss-of-function mutants of AGL15, alone or when combined with a loss-of-function mutant of a closely related family member, AGL18, show decreased ability to produce somatic embryos. If constitutive expression of orthologs of AGL15 is able to enhance somatic embryo development in other species, thereby facilitating recovery of transgenic plants, then AGL15 may provide a valuable tool for crop improvement. To test this idea in soybean (Glycine max), a full-length cDNA encoding a putative ortholog of AGL15 was isolated from …

Systems Approach Identifies An Organic Nitrogen-Responsive Gene Network That Is Regulated By The Master Clock Control Gene Cca1, Rodrigo A. Gutierrez, Trevor L. Stokes, Karen Thum, Xiaodong Xu, Mariana Obertello, Manpreet S. Katari, Milos Tanurdzic, Alexis Dean, Damion C. Nero, C Robertson Mcclung, Gloria M. Coruzzi

Dartmouth Scholarship

Understanding how nutrients affect gene expression will help us to understand the mechanisms controlling plant growth and development as a function of nutrient availability. Nitrate has been shown to serve as a signal for the control of gene expression in Arabidopsis. There is also evidence, on a gene-by-gene basis, that downstream products of nitrogen (N) assimilation such as glutamate (Glu) or glutamine (Gln) might serve as signals of organic N status that in turn regulate gene expression. To identify genome-wide responses to such organic N signals, Arabidopsis seedlings were transiently treated with ammonium nitrate in the presence or absence of …

Variation In Molybdenum Content Across Broadly Distributed Populations Of Arabidopsis Thaliana Is Controlled By A Mitochondrial Molybdenum Transporter (Mot1), Ivan Baxter, Balasubramaniam Muthukumar, Hyeong Cheol Park, Peter Buchner, Brett Lahner, John Danku, Keyan Zhao, Joohyun Lee, Malcolm J. Hawkesford, Mary Lou Guerinot, David E. Salt

Dartmouth Scholarship

Molybdenum (Mo) is an essential micronutrient for plants, serving as a cofactor for enzymes involved in nitrate assimilation, sulfite detoxification, abscisic acid biosynthesis, and purine degradation. Here we show that natural variation in shoot Mo content across 92 Arabidopsis thaliana accessions is controlled by variation in a mitochondrially localized transporter (Molybdenum Transporter 1 - MOT1) that belongs to the sulfate transporter superfamily. A deletion in the MOT1 promoter is strongly associated with low shoot Mo, occurring in seven of the accessions with the lowest shoot content of Mo. Consistent with the low Mo phenotype, MOT1 expression in low Mo accessions …

Micrornas And The Advent Of Vertebrate Morphological Complexity, Alysha M. Heimberg, Lorenzo F. Sempere, Vanessa N. Moy, Phillip C. J. Donoghue, Kevin J. Peterson

Dartmouth Scholarship

The causal basis of vertebrate complexity has been sought in genome duplication events (GDEs) that occurred during the emergence of vertebrates, but evidence beyond coincidence is wanting. MicroRNAs (miRNAs) have recently been identified as a viable causal factor in increasing organismal complexity through the action of these ≈22-nt noncoding RNAs in regulating gene expression. Because miRNAs are continuously being added to animalian genomes, and, once integrated into a gene regulatory network, are strongly conserved in primary sequence and rarely secondarily lost, their evolutionary history can be accurately reconstructed. Here, using a combination of Northern analyses and genomic searches, we show …

Arsenic As An Endocrine Disruptor: Arsenic Disrupts Retinoic Acid Receptor–And Thyroid Hormone Receptor–Mediated Gene Regulation And Thyroid Hormone–Mediated Amphibian Tail Metamorphosis, Jennifer C. Davey, Athena P. Nomikos, Manida Wungjiranirun, Jenna R. Sherman, Liam Ingram, Cavus Batki, Jean P. Lariviere, Joshua W. Hamilton

Dartmouth Scholarship

Background:

Chronic exposure to excess arsenic in drinking water has been strongly associated with increased risks of multiple cancers, diabetes, heart disease, and reproductive and developmental problems in humans. We previously demonstrated that As, a potent endocrine disruptor at low, environmentally relevant levels, alters steroid signaling at the level of receptor-mediated gene regulation for all five steroid receptors.

Objectives:

The goal of this study was to determine whether As can also disrupt gene regulation via the retinoic acid (RA) receptor (RAR) and/or the thyroid hormone (TH) receptor (TR) and whether these effects are similar to previously observed effects on steroid …