TY - JOUR A1 - Hassan, Musa A. A1 - Vasquez, Juan J. A1 - Guo-Liang, Chew A1 - Meissner, Markus A1 - Siegel, T. Nicolai T1 - Comparative ribosome profiling uncovers a dominant role for translational control in \(Toxoplasma\) \(gondii\) JF - BMC Genomics N2 - Background The lytic cycle of the protozoan parasite \(Toxoplasma\) \(gondii\), which involves a brief sojourn in the extracellular space, is characterized by defined transcriptional profiles. For an obligate intracellular parasite that is shielded from the cytosolic host immune factors by a parasitophorous vacuole, the brief entry into the extracellular space is likely to exert enormous stress. Due to its role in cellular stress response, we hypothesize that translational control plays an important role in regulating gene expression in \(Toxoplasma\) during the lytic cycle. Unlike transcriptional profiles, insights into genome-wide translational profiles of \(Toxoplasma\) \(gondii\) are lacking. Methods We have performed genome-wide ribosome profiling, coupled with high throughput RNA sequencing, in intracellular and extracellular \(Toxoplasma\) \(gondii\) parasites to investigate translational control during the lytic cycle. Results Although differences in transcript abundance were mostly mirrored at the translational level, we observed significant differences in the abundance of ribosome footprints between the two parasite stages. Furthermore, our data suggest that mRNA translation in the parasite is potentially regulated by mRNA secondary structure and upstream open reading frames. Conclusion We show that most of the \(Toxoplasma\) genes that are dysregulated during the lytic cycle are translationally regulated. KW - Biology KW - Ribosome profiling KW - RNA-sequencing KW - Translation efficiency KW - Toxoplasma gondii KW - Apicomplexan Y1 - 2017 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-172376 VL - 18 ER - TY - JOUR A1 - Kraus, Amelie J. A1 - Brink, Benedikt G. A1 - Siegel, T. Nicolai T1 - Efficient and specific oligo-based depletion of rRNA JF - Scientific Reports N2 - In most organisms, ribosomal RNA (rRNA) contributes to >85% of total RNA. Thus, to obtain useful information from RNA-sequencing (RNA-seq) analyses at reasonable sequencing depth, typically, mature polyadenylated transcripts are enriched or rRNA molecules are depleted. Targeted depletion of rRNA is particularly useful when studying transcripts lacking a poly(A) tail, such as some non-coding RNAs (ncRNAs), most bacterial RNAs and partially degraded or immature transcripts. While several commercially available kits allow effective rRNA depletion, their efficiency relies on a high degree of sequence homology between oligonucleotide probes and the target RNA. This restricts the use of such kits to a limited number of organisms with conserved rRNA sequences. In this study we describe the use of biotinylated oligos and streptavidin-coated paramagnetic beads for the efficient and specific depletion of trypanosomal rRNA. Our approach reduces the levels of the most abundant rRNA transcripts to less than 5% with minimal off-target effects. By adjusting the sequence of the oligonucleotide probes, our approach can be used to deplete rRNAs or other abundant transcripts independent of species. Thus, our protocol provides a useful alternative for rRNA removal where enrichment of polyadenylated transcripts is not an option and commercial kits for rRNA are not available. KW - parasite biology KW - RNA sequencing KW - transcriptomics Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-224829 VL - 9 ER - TY - JOUR A1 - Müller, Laura S. M. A1 - Cosentino, Raúl O. A1 - Förstner, Konrad U. A1 - Guizetti, Julien A1 - Wedel, Carolin A1 - Kaplan, Noam A1 - Janzen, Christian J. A1 - Arampatzi, Panagiota A1 - Vogel, Jörg A1 - Steinbiss, Sascha A1 - Otto, Thomas D. A1 - Saliba, Antoine-Emmanuel A1 - Sebra, Robert P. A1 - Siegel, T. Nicolai T1 - Genome organization and DNA accessibility control antigenic variation in trypanosomes JF - Nature N2 - Many evolutionarily distant pathogenic organisms have evolved similar survival strategies to evade the immune responses of their hosts. These include antigenic variation, through which an infecting organism prevents clearance by periodically altering the identity of proteins that are visible to the immune system of the host1. Antigenic variation requires large reservoirs of immunologically diverse antigen genes, which are often generated through homologous recombination, as well as mechanisms to ensure the expression of one or very few antigens at any given time. Both homologous recombination and gene expression are affected by three-dimensional genome architecture and local DNA accessibility2,3. Factors that link three-dimensional genome architecture, local chromatin conformation and antigenic variation have, to our knowledge, not yet been identified in any organism. One of the major obstacles to studying the role of genome architecture in antigenic variation has been the highly repetitive nature and heterozygosity of antigen-gene arrays, which has precluded complete genome assembly in many pathogens. Here we report the de novo haplotype-specific assembly and scaffolding of the long antigen-gene arrays of the model protozoan parasite Trypanosoma brucei, using long-read sequencing technology and conserved features of chromosome folding4. Genome-wide chromosome conformation capture (Hi-C) reveals a distinct partitioning of the genome, with antigen-encoding subtelomeric regions that are folded into distinct, highly compact compartments. In addition, we performed a range of analyses—Hi-C, fluorescence in situ hybridization, assays for transposase-accessible chromatin using sequencing and single-cell RNA sequencing—that showed that deletion of the histone variants H3.V and H4.V increases antigen-gene clustering, DNA accessibility across sites of antigen expression and switching of the expressed antigen isoform, via homologous recombination. Our analyses identify histone variants as a molecular link between global genome architecture, local chromatin conformation and antigenic variation. KW - histone variants KW - genome architecture KW - single molecule real time (SMRT) KW - brucei genome KW - distance-dependent decay Y1 - 2018 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-224265 VL - 563 ER - TY - JOUR A1 - Vembar, Shruti S. A1 - Scherf, Artur A1 - Siegel, T. Nicolai T1 - Noncoding RNAs as emerging regulators of Plasmodium falciparum virulence gene expression JF - Current Opinion in Microbiology N2 - The eukaryotic unicellular pathogen Plasmodium falciparum tightly regulates gene expression, both during development and in adaptation to dynamic host environments. This regulation is evident in the mutually exclusive expression of members of clonally variant virulence multigene families. While epigenetic regulators have been selectively identified at active or repressed virulence genes, their specific recruitment remains a mystery. In recent years, noncoding RNAs (ncRNAs) have emerged as lynchpins of eukaryotic gene regulation; by binding to epigenetic regulators, they provide target specificity to otherwise non-specific enzyme complexes. Not surprisingly, there is great interest in understanding the role of ncRNA in P. falciparum, in particular, their contribution to the mutually exclusive expression of virulence genes. The current repertoire of P. falciparum ncRNAs includes, but is not limited to, subtelomeric ncRNAs, virulence gene-associated ncRNAs and natural antisense RNA transcripts. Continued improvement in high-throughput sequencing methods is sure to expand this repertoire. Here, we summarize recent advances in P. falciparum ncRNA biology, with an emphasis on ncRNA-mediated epigenetic modes of gene regulation. Y1 - 2014 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-121416 SN - 1369-5274 VL - 20 IS - 100 ER - TY - JOUR A1 - Nguyen, Tu N. A1 - Müller, Laura S. M. A1 - Park, Sung Hee A1 - Siegel, T. Nicolai A1 - Günzl, Arthur T1 - Promoter occupancy of the basal class I transcription factor A differs strongly between active and silent VSG expression sites in Trypanosoma brucei JF - Nucleic Acid Research N2 - Monoallelic expression within a gene family is found in pathogens exhibiting antigenic variation and in mammalian olfactory neurons. Trypanosoma brucei, a lethal parasite living in the human bloodstream, expresses variant surface glycoprotein (VSG) from 1 of 15 bloodstream expression sites (BESs) by virtue of a multifunctional RNA polymerase I. The active BES is transcribed in an extranucleolar compartment termed the expression site body (ESB), whereas silent BESs, located elsewhere within the nucleus, are repressed epigenetically. The regulatory mechanisms, however, are poorly understood. Here we show that two essential subunits of the basal class I transcription factor A (CITFA) predominantly occupied the promoter of the active BES relative to that of a silent BES, a phenotype that was maintained after switching BESs in situ. In these experiments, high promoter occupancy of CITFA was coupled to high levels of both promoter-proximal RNA abundance and RNA polymerase I occupancy. Accordingly, fluorescently tagged CITFA-7 was concentrated in the nucleolus and the ESB. Because a ChIP-seq analysis found that along the entire BES, CITFA-7 is specifically enriched only at the promoter, our data strongly indicate that monoallelic BES transcription is activated by a mechanism that functions at the level of transcription initiation. KW - RNA-polymerase-I KW - blood-stream forms KW - acrican trypanosomes KW - gene expression KW - antigenic variation KW - ribosomal RNA KW - plasmodium falciparum KW - virulence genes KW - subunit KW - complex Y1 - 2014 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-117232 SN - 1362-4962 VL - 42 IS - 5 ER - TY - JOUR A1 - Reynolds, David A1 - Cliffe, Laura A1 - Förstner, Konrad U. A1 - Hon, Chung-Chau A1 - Siegel, T. Nicolai A1 - Sabatini, Robert T1 - Regulation of transcription termination by glucosylated hydroxymethyluracil, base J, in Leishmania major and Trypanosoma brucei JF - Nucleic Acids Research N2 - Base J, beta-d-glucosyl-hydroxymethyluracil, is an epigenetic modification of thymine in the nuclear DNA of flagellated protozoa of the order Kinetoplastida. J is enriched at sites involved in RNA polymerase ( RNAP) II initiation and termination. Reduction of J in Leishmania tarentolae via growth in BrdU resulted in cell death and indicated a role of J in the regulation of RNAP II termination. To further explore J function in RNAP II termination among kinetoplastids and avoid indirect effects associated with BrdU toxicity and genetic deletions, we inhibited J synthesis in Leishmania major and Trypanosoma brucei using DMOG. Reduction of J in L. major resulted in genome-wide defects in transcription termination at the end of polycistronic gene clusters and the generation of antisense RNAs, without cell death. In contrast, loss of J in T. brucei did not lead to genome-wide termination defects; however, the loss of J at specific sites within polycistronic gene clusters led to altered transcription termination and increased expression of downstream genes. Thus, J regulation of RNAP II transcription termination genome-wide is restricted to Leishmania spp., while in T. brucei it regulates termination and gene expression at specific sites within polycistronic gene clusters. KW - RNA-polymerase-II KW - variant surface glycoprotein KW - SWI2/SNF2-like protein KW - messenger RNA KW - polycistronic transcription KW - DNA glycosation KW - hela cells KW - gene expression KW - genome KW - 5-bromodeoxyuridine Y1 - 2014 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-117863 VL - 42 IS - 15 ER - TY - JOUR A1 - Siegel, T. Nicolai A1 - Hon, Chung-Chau A1 - Zhang, Qinfeng A1 - Lopez-Rubio, Jose-Juan A1 - Scheidig-Benatar, Christine A1 - Martins, Rafeal M. A1 - Sismeiro, Odile A1 - Coppée, Jean-Yves T1 - Strand-specific RNA-Seq reveals widespread and developmentally regulated transcription of natural antisense transcripts in Plasmodium falciparum JF - BMC Genomics N2 - Background Advances in high-throughput sequencing have led to the discovery of widespread transcription of natural antisense transcripts (NATs) in a large number of organisms, where these transcripts have been shown to play important roles in the regulation of gene expression. Likewise, the existence of NATs has been observed in Plasmodium but our understanding towards their genome-wide distribution remains incomplete due to the limited depth and uncertainties in the level of strand specificity of previous datasets. Results To gain insights into the genome-wide distribution of NATs in P. falciparum, we performed RNA-ligation based strand-specific RNA sequencing at unprecedented depth. Our data indicate that 78.3% of the genome is transcribed during blood-stage development. Moreover, our analysis reveals significant levels of antisense transcription from at least 24% of protein-coding genes and that while expression levels of NATs change during the intraerythrocytic developmental cycle (IDC), they do not correlate with the corresponding mRNA levels. Interestingly, antisense transcription is not evenly distributed across coding regions (CDSs) but strongly clustered towards the 3′-end of CDSs. Furthermore, for a significant subset of NATs, transcript levels correlate with mRNA levels of neighboring genes. Finally, we were able to identify the polyadenylation sites (PASs) for a subset of NATs, demonstrating that at least some NATs are polyadenylated. We also mapped the PASs of 3443 coding genes, yielding an average 3′ untranslated region length of 523 bp. Conclusions Our strand-specific analysis of the P. falciparum transcriptome expands and strengthens the existing body of evidence that antisense transcription is a substantial phenomenon in P. falciparum. For a subset of neighboring genes we find that sense and antisense transcript levels are intricately linked while other NATs appear to be regulated independently of mRNA transcription. Our deep strand-specific dataset will provide a valuable resource for the precise determination of expression levels as it separates sense from antisense transcript levels, which we find to often significantly differ. In addition, the extensive novel data on 3′ UTR length will allow others to perform searches for regulatory motifs in the UTRs and help understand post-translational regulation in P. falciparum. KW - directional RNA-Seq KW - ncRNA KW - natural antisense transcripts KW - 3′ UTR KW - polyadenylation sites KW - genes KW - antisense RNA KW - plasmodium falciparum Y1 - 2014 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-119892 VL - 15 ER -