@article {49535, title = {Genomic analysis of sequence-dependent DNA curvature in Leishmania.}, volume = {8}, year = {2013}, month = {2013}, pages = {e63068}, abstract = {

Leishmania major is a flagellated protozoan parasite of medical importance. Like other members of the Trypanosomatidae family, it possesses unique mechanisms of gene expression such as constitutive polycistronic transcription of directional gene clusters, gene amplification, mRNA trans-splicing, and extensive editing of mitochondrial transcripts. The molecular signals underlying most of these processes remain under investigation. In order to investigate the role of DNA secondary structure signals in gene expression, we carried out a genome-wide in silico analysis of the intrinsic DNA curvature. The L. major genome revealed a lower frequency of high intrinsic curvature regions as well as inter- and intra- chromosomal distribution heterogeneity, when compared to prokaryotic and eukaryotic organisms. Using a novel method aimed at detecting region-integrated intrinsic curvature (RIIC), high DNA curvature was found to be associated with regions implicated in transcription initiation. Those include divergent strand-switch regions between directional gene clusters and regions linked to markers of active transcription initiation such as acetylated H3 histone, TRF4 and SNAP50. These findings suggest a role for DNA curvature in transcription initiation in Leishmania supporting the relevance of DNA secondary structures signals.

}, keywords = {Chromosome mapping, Comparative Genomic Hybridization, Computational Biology, DNA, Protozoan, Genome, Protozoan, Genomics, HUMANS, Leishmania, Nucleic Acid Conformation}, issn = {1932-6203}, doi = {10.1371/journal.pone.0063068}, author = {Smircich, Pablo and Forteza, Diego and El-Sayed, Najib M and Garat, Beatriz} } @article {49649, title = {Genome-wide analysis reveals novel genes essential for heme homeostasis in Caenorhabditis elegans.}, journal = {PLoS Genet}, volume = {6}, year = {2010}, month = {2010 Jul}, pages = {e1001044}, abstract = {

Heme is a cofactor in proteins that function in almost all sub-cellular compartments and in many diverse biological processes. Heme is produced by a conserved biosynthetic pathway that is highly regulated to prevent the accumulation of heme--a cytotoxic, hydrophobic tetrapyrrole. Caenorhabditis elegans and related parasitic nematodes do not synthesize heme, but instead require environmental heme to grow and develop. Heme homeostasis in these auxotrophs is, therefore, regulated in accordance with available dietary heme. We have capitalized on this auxotrophy in C. elegans to study gene expression changes associated with precisely controlled dietary heme concentrations. RNA was isolated from cultures containing 4, 20, or 500 microM heme; derived cDNA probes were hybridized to Affymetrix C. elegans expression arrays. We identified 288 heme-responsive genes (hrgs) that were differentially expressed under these conditions. Of these genes, 42\% had putative homologs in humans, while genomes of medically relevant heme auxotrophs revealed homologs for 12\% in both Trypanosoma and Leishmania and 24\% in parasitic nematodes. Depletion of each of the 288 hrgs by RNA-mediated interference (RNAi) in a transgenic heme-sensor worm strain identified six genes that regulated heme homeostasis. In addition, seven membrane-spanning transporters involved in heme uptake were identified by RNAi knockdown studies using a toxic heme analog. Comparison of genes that were positive in both of the RNAi screens resulted in the identification of three genes in common that were vital for organismal heme homeostasis in C. elegans. Collectively, our results provide a catalog of genes that are essential for metazoan heme homeostasis and demonstrate the power of C. elegans as a genetic animal model to dissect the regulatory circuits which mediate heme trafficking in both vertebrate hosts and their parasites, which depend on environmental heme for survival.

}, keywords = {Animals, Caenorhabditis elegans, Dose-Response Relationship, Drug, Gene Expression Profiling, Gene Expression Regulation, genes, Genome-Wide Association Study, Heme, Homeostasis, HUMANS, Leishmania, Nematoda, Trypanosoma}, issn = {1553-7404}, doi = {10.1371/journal.pgen.1001044}, author = {Severance, Scott and Rajagopal, Abbhirami and Rao, Anita U and Cerqueira, Gustavo C and Mitreva, Makedonka and El-Sayed, Najib M and Krause, Michael and Hamza, Iqbal} } @article {38472, title = {Role of transposable elements in trypanosomatids}, journal = {Microbes and InfectionMicrobes and Infection}, volume = {10}, year = {2008}, type = {16/j.micinf.2008.02.009}, abstract = {Transposable elements constitute 2-5\% of the genome content in trypanosomatid parasites. Some of them are involved in critical cellular functions, such as the regulation of gene expression in Leishmania spp. In this review, we highlight the remarkable role extinct transposable elements can play as the source of potential new functions.}, keywords = {Cellular function, Domestication, Evolution, Gene expression, Leishmania, Regulation of mRNA stability, Retroposon, Transposable element, Trypanosoma}, isbn = {1286-4579}, author = {Bringaud, Frederic and Ghedin, Elodie and Najib M. El-Sayed and Papadopoulou, Barbara} } @article {49642, title = {Members of a large retroposon family are determinants of post-transcriptional gene expression in Leishmania.}, journal = {PLoS Pathog}, volume = {3}, year = {2007}, month = {2007 Sep 7}, pages = {1291-307}, abstract = {

Trypanosomatids are unicellular protists that include the human pathogens Leishmania spp. (leishmaniasis), Trypanosoma brucei (sleeping sickness), and Trypanosoma cruzi (Chagas disease). Analysis of their recently completed genomes confirmed the presence of non-long-terminal repeat retrotransposons, also called retroposons. Using the 79-bp signature sequence common to all trypanosomatid retroposons as bait, we identified in the Leishmania major genome two new large families of small elements--LmSIDER1 (785 copies) and LmSIDER2 (1,073 copies)--that fulfill all the characteristics of extinct trypanosomatid retroposons. LmSIDERs are approximately 70 times more abundant in L. major compared to T. brucei and are found almost exclusively within the 3{\textquoteright}-untranslated regions (3{\textquoteright}UTRs) of L. major mRNAs. We provide experimental evidence that LmSIDER2 act as mRNA instability elements and that LmSIDER2-containing mRNAs are generally expressed at lower levels compared to the non-LmSIDER2 mRNAs. The considerable expansion of LmSIDERs within 3{\textquoteright}UTRs in an organism lacking transcriptional control and their role in regulating mRNA stability indicate that Leishmania have probably recycled these short retroposons to globally modulate the expression of a number of genes. To our knowledge, this is the first example in eukaryotes of the domestication and expansion of a family of mobile elements that have evolved to fulfill a critical cellular function.

}, keywords = {3{\textquoteright} Untranslated Regions, Animals, Base Sequence, Biological Evolution, Down-Regulation, Gene Expression Regulation, Genome, Protozoan, Leishmania, Leishmania major, Molecular Sequence Data, Retroelements, RNA, Messenger, sequence alignment, Trypanosoma brucei brucei, Trypanosoma cruzi}, issn = {1553-7374}, doi = {10.1371/journal.ppat.0030136}, author = {Bringaud, Frederic and M{\"u}ller, Michaela and Cerqueira, Gustavo Coutinho and Smith, Martin and Rochette, Annie and el-Sayed, Najib M A and Papadopoulou, Barbara and Ghedin, Elodie} } @article {49640, title = {Trypanosoma cruzi mitochondrial maxicircles display species- and strain-specific variation and a conserved element in the non-coding region.}, journal = {BMC Genomics}, volume = {7}, year = {2006}, month = {2006}, pages = {60}, abstract = {

BACKGROUND: The mitochondrial DNA of kinetoplastid flagellates is distinctive in the eukaryotic world due to its massive size, complex form and large sequence content. Comprised of catenated maxicircles that contain rRNA and protein-coding genes and thousands of heterogeneous minicircles encoding small guide RNAs, the kinetoplast network has evolved along with an extreme form of mRNA processing in the form of uridine insertion and deletion RNA editing. Many maxicircle-encoded mRNAs cannot be translated without this post-transcriptional sequence modification.

RESULTS: We present the complete sequence and annotation of the Trypanosoma cruzi maxicircles for the CL Brener and Esmeraldo strains. Gene order is syntenic with Trypanosoma brucei and Leishmania tarentolae maxicircles. The non-coding components have strain-specific repetitive regions and a variable region that is unique for each strain with the exception of a conserved sequence element that may serve as an origin of replication, but shows no sequence identity with L. tarentolae or T. brucei. Alternative assemblies of the variable region demonstrate intra-strain heterogeneity of the maxicircle population. The extent of mRNA editing required for particular genes approximates that seen in T. brucei. Extensively edited genes were more divergent among the genera than non-edited and rRNA genes. Esmeraldo contains a unique 236-bp deletion that removes the 5{\textquoteright}-ends of ND4 and CR4 and the intergenic region. Esmeraldo shows additional insertions and deletions outside of areas edited in other species in ND5, MURF1, and MURF2, while CL Brener has a distinct insertion in MURF2.

CONCLUSION: The CL Brener and Esmeraldo maxicircles represent two of three previously defined maxicircle clades and promise utility as taxonomic markers. Restoration of the disrupted reading frames might be accomplished by strain-specific RNA editing. Elements in the non-coding region may be important for replication, transcription, and anchoring of the maxicircle within the kinetoplast network.

}, keywords = {Amino Acid Sequence, Animals, Animals, Inbred Strains, Base Composition, Conserved Sequence, DNA, Kinetoplast, Frameshifting, Ribosomal, Gene Deletion, Gene Order, Genetic Variation, Leishmania, Models, Biological, Molecular Sequence Data, Muscle Proteins, NADH Dehydrogenase, Open Reading Frames, Regulatory Elements, Transcriptional, RNA Editing, Sequence Homology, Amino Acid, Species Specificity, Trypanosoma brucei brucei, Trypanosoma cruzi, Ubiquitin-Protein Ligases, Untranslated Regions}, issn = {1471-2164}, doi = {10.1186/1471-2164-7-60}, author = {Westenberger, Scott J and Cerqueira, Gustavo C and El-Sayed, Najib M and Zingales, Bianca and Campbell, David A and Sturm, Nancy R} } @article {49627, title = {Genetic nomenclature for Trypanosoma and Leishmania.}, journal = {Mol Biochem Parasitol}, volume = {97}, year = {1998}, month = {1998 Nov 30}, pages = {221-4}, keywords = {Animals, Leishmania, Terminology as Topic, Trypanosoma}, issn = {0166-6851}, author = {Clayton, C and Adams, M and Almeida, R and Baltz, T and Barrett, M and Bastien, P and Belli, S and Beverley, S and Biteau, N and Blackwell, J and Blaineau, C and Boshart, M and Bringaud, F and Cross, G and Cruz, A and Degrave, W and Donelson, J and El-Sayed, N and Fu, G and Ersfeld, K and Gibson, W and Gull, K and Ivens, A and Kelly, J and Vanhamme, L} } @article {38392, title = {Multiple mechanisms of immune evasion by African trypanosomes}, journal = {Molecular and Biochemical ParasitologyMolecular and Biochemical Parasitology}, volume = {91}, year = {1998}, type = {16/S0166-6851(97)00209-0}, abstract = {During infection of a mammalian host, African trypanosomes are in constant contact with the host{\textquoteright}s immune system. These protozoan parasites are infamous for their ability to evade the immune responses by periodically switching their major variant surface glycoprotein (VSG), a phenomenon called antigenic variation. Antigenic variation, however, is likely to be only one of several mechanisms enabling these organisms to thrive in the face of the immune defenses. The ability to grow in high levels of interferon-gamma (IFN-[gamma]) and to avoid complement-mediated destruction may also facilitate the parasite{\textquoteright}s survival. In this review we summarize (i) the activation of trypanosome genes for three different VSGs during antigenic variation, (ii) the secretion of a trypanosome protein that induces host CD8+ T cells to produce IFN-[gamma], and (iii) the evidence for trypansome protein similar to a surface protease of Leishmania that plays a role in resistance to complement-mediated lysis.}, keywords = {Leishmania, Recombinant cloning, T cell, Trypanosomes, VSG genes}, isbn = {0166-6851}, author = {Donelson, John E. and Hill, Kent L. and Najib M. El-Sayed} }