Gene transcription in trypanosomes

Palenchar, Jennifer B.; Bellofatto, Vivian

doi:10.1016/j.molbiopara.2005.12.008

Cited by 113 publications

(95 citation statements)

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“…Kinetoplastid parasites show an important variation on this eukaryotic paradigm because these cells have polycistronic transcription coupled with the apparent absence of classic RNA polymerase II promoters, indicating that transcriptional regulation is not relevant (26,27). Trypanosomatids are also different from other organisms having transcriptomes composed of multigene transcription units, such as Drosophila and Caenorhabditis elegans.…”

Section: Discussionmentioning

confidence: 99%

mRNA maturation by two-step trans-splicing/polyadenylation processing in trypanosomes

Jäger

Gaudenzi

Cassola

et al. 2007

Proc. Natl. Acad. Sci. U.S.A.

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Trypanosomes are unique eukaryotic cells, in that they virtually lack mechanisms to control gene expression at the transcriptional level. These microorganisms mostly control protein synthesis by posttranscriptional regulation processes, like mRNA stabilization and degradation. Transcription in these cells is polycistronic. Tens to hundreds of protein-coding genes of unrelated function are arrayed in long clusters on the same DNA strand. Polycistrons are cotranscriptionally processed by trans-splicing at the 5 end and polyadenylation at the 3 end, generating monocistronic units ready for degradation or translation. In this work, we show that some trans-splicing/polyadenylation sites may be skipped during normal polycistronic processing. As a consequence, dicistronic units or monocistronic transcripts having long 3 UTRs are produced. Interestingly, these unspliced transcripts can be processed into mature mRNAs by the conventional trans-splicing/ polyadenylation events leading to translation. To our knowledge, this is a previously undescribed mRNA maturation by trans-splicing uncoupled from transcription. We identified an RNA-recognition motif-type protein, homologous to the mammalian polypyrimidine tract-binding protein, interacting with one of the partially processed RNAs analyzed here that might be involved in exon skipping. We propose that splice-site skipping might be part of a posttranscriptional mechanism to regulate gene expression in trypanosomes, through the generation of premature nontranslatable RNA molecules.gene expression ͉ posttranscriptional regulation ͉ RNA processing R egulation of gene expression is central in defining the phenotype of a cell or organism. In the vast majority of cases, this regulation is controlled by transcriptional regulation in which DNA sequence elements, together with DNA-binding proteins, target genes for transcription by RNA polymerase II. In addition to regulating single genes, master regulators of transcription may give rise to a gene expression phenotype, a trait that may be inherited (1). Mature transcripts can also be regulated in their expression at the posttranscriptional level. A number of cis-motifs mainly located in the 5Ј and 3Ј UTRs determine the fate of the transcript by the use of highly specific and sometimes evolutionarily conserved machineries. This process is essentially achieved through RNA-binding proteins (RBPs) forming, together with the mRNA, ribonucleoprotein (RNP) complexes. It is the composition of the RNP complex that determines whether an mRNA is transported to the cytoplasm for translation, degradation, or other processing events (2, 3).Posttranscriptional regulation is common among Kinetoplastid parasites, like trypanosomes and Leishmania (4, 5), which are the causative agents of several infections affecting both humans and domestic animals worldwide (6). In these parasites, transcription by RNA polymerase II starts at a few genomic locations within chromosomes. In contrast to operons in bacteria, polycistronic units in trypanosomatids requir...

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Section: Discussionmentioning

confidence: 99%

mRNA maturation by two-step trans-splicing/polyadenylation processing in trypanosomes

Jäger

Gaudenzi

Cassola

et al. 2007

Proc. Natl. Acad. Sci. U.S.A.

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“…With the exception of the spliced leader (SL) promoter, no promoter that is recognised by RNA polymerase II has been identified, and only a few transcription factors have been described (Cribb & Serra 2009, Cribb et al 2010. Notably, even though orthologs for all of the conserved components of the RNA polymerase II complex have been identified in the Tri-Tryp genome (Ivens et al 2005), the transcription of two trypanosomatid genes, variant surface protein and procyclin genes in T. brucei, as well as several exogenous genes that are transfected into T. cruzi, is mediated by RNA polymerase I (Palenchar & Bellofatto 2006). Once the polycistronic pre-mRNA is produced, the following two coupled reactions allow for the generation of mature monocistronic transcripts: trans-splicing and polyadenylation (Teixeira & DaRocha 2003).…”

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confidence: 99%

Regulatory elements involved in the post-transcriptional control of stage-specific gene expression in Trypanosoma cruzi: a review

Araújo

Teixeira

2011

Mem. Inst. Oswaldo Cruz

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Trypanosoma cruzi is an intracellular parasite that is transmitted by at least 40 different blood-sucking triatomine species to over 1,000 mammalian species (Brener et al. 2000). This parasite must adapt to enormous changes in its extracellular milieu, such as changes in environmental temperature as well as in the available nutrients inside each host. The parasite has a complex life cycle that is characterised by four stages; epimastigotes and metacyclic trypomastigotes are present in the insect vector, whereas intracellular amastigotes and bloodstream trypomastigotes are present in the mammalian host. Thus, this species must develop a broad set of molecular tools that allow it to multiply in the insect gut, to invade and multiply inside a large number of distinct mammalian cell types and to circumvent host immune defence systems. To meet such phenotypic plasticity, T. cruzi relies on unique mechanisms that can control the expression of its repertoire of about 12,000 genes. Because its genome is constitutively transcribed into long polycistronic primary transcripts, mRNAs for proteincoding genes must be processed through trans-splicing and polyadenylation reactions. The mRNAs must also interact with different protein factors in a complex posttranscriptional regulatory machinery that determines the levels of their protein product according to the cellular demands of the parasite in each stage of its life cycle.In the same issue that the T. cruzi genome was published (El-Sayed et al. 2005a), a study describing its proteome was also reported (Atwood et al. 2005). Proteins extracted from whole-cell and subcellular lysates of the four stages of T. cruzi were analysed by mass spectrometry (epimastigotes, metacyclic trypomastigotes, amastigotes and trypomastigotes), which identified 2,784 proteins belonging to the 1,168 protein groups in the annotated T. cruzi genome. Although about 30% of the identified proteins were found at all life-cycle stages, at least 248 proteins were only expressed at one stage, thereby demonstrating significant changes in the relative abundance of T. cruzi proteins throughout its life cycle. One of the main findings in these proteomic analyses was that the four parasite stages use distinct energy sources (Atwood et al. 2005); intracellular amastigotes upregulated proteins involved in lipid-dependent energy metabolism, such as enzymes of the citric acid cycle, whereas enzymes capable of catalysing the conversion of histidine to glutamate were more abundant in the insect epimastigote stage. Heat-shock proteins (HSP) and proteins involved in vesicular trafficking were also preferentially detected in amastigotes. Furthermore, enzymes involved in antioxidant defence were upregulated during the transformation of epimastigotes into invasive metacyclic trypomastigotes, whereas bloodstream trypomastigotes upregulated the surface expression of several large gene families that are known to be involved in interacting with the mammalian host (Atwood et al. 2005).In agreement with this proteomics data, glo...

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“…Trypanosoma brucei and Trypanosoma cruzi are of particular medical concern because they cause debilitating and fatal diseases in millions of people annually in tropical regions of the world (2). Trypanosomes diverged from other eukaryotes early in evolution, and thus many biological processes that are well understood in metazoans are highly distinct in these parasites (3,4). For example, little is known about how trypanosome RNA polymerase II (tRNAP-II) transcription is initiated.…”

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confidence: 99%

“…The SL RNA gene codes for the SL, which is capped and added in a trans-splicing reaction to the 5Ј end of each ORF contained in a polycistronic mRNA. The addition of an SL to every mRNA is a universal requirement in trypanosomes; therefore, understanding transcription initiation at the SL RNA gene promoter is a crucial step toward understanding the control of tRNAP-II transcription in these parasites (4,7).…”

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confidence: 99%

Structure of the C-terminal domain of transcription factor IIB from Trypanosoma brucei

Ibrahim¹,

Kanneganti²,

Rieckhof

et al. 2009

Proc. Natl. Acad. Sci. U.S.A.

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In trypanosomes, the production of mRNA relies on the synthesis of the spliced leader (SL) RNA. Expression of the SL RNA is initiated at the only known RNA polymerase II promoter in these parasites. In the pathogenic trypanosome, Trypanosoma brucei, transcription factor IIB (tTFIIB) is essential for SL RNA gene transcription and cell viability, but has a highly divergent primary sequence in comparison to TFIIB in well-studied eukaryotes. Here we describe the 2.3 Å resolution structure of the C-terminal domain of tTFIIB (tTFIIB C ). The tTFIIB C structure consists of 2 closely packed helical modules followed by a C-terminal extension of 32 aa. Using the structure as a guide, alanine substitutions of basic residues in regions analogous to functionally important regions of the well-studied eukaryotic TFIIB support conservation of a general mechanism of TFIIB function in eukaryotes. Strikingly, tTFIIB C contains additional loops and helices, and, in contrast to the highly basic DNA binding surface of human TFIIB, contains a neutral surface in the corresponding region. These attributes probably mediate trypanosomespecific interactions and have implications for the apparent bidirectional transcription by RNA polymerase II in protein-encoding gene expression in these organisms.eukaryotic transcription ͉ parasite ͉ RNA polymerase II ͉ trypanosome T rypanosomes are flagellated protozoa, belonging to the order Kinetoplastida, that are exclusively parasitic (1). These organisms reside in insect vectors that transmit the parasites to mammals, birds, fish, and plants. Trypanosoma brucei and Trypanosoma cruzi are of particular medical concern because they cause debilitating and fatal diseases in millions of people annually in tropical regions of the world (2). Trypanosomes diverged from other eukaryotes early in evolution, and thus many biological processes that are well understood in metazoans are highly distinct in these parasites (3, 4). For example, little is known about how trypanosome RNA polymerase II (tRNAP-II) transcription is initiated. It is known that tRNAP-II transcribes most protein-encoding genes, which are arranged in tandem arrays, into polycistronic mRNAs (5). Thus far, the only tRNAP-II promoter that has been identified is the spliced leader (SL) RNA gene promoter (6). The SL RNA gene codes for the SL, which is capped and added in a trans-splicing reaction to the 5Ј end of each ORF contained in a polycistronic mRNA. The addition of an SL to every mRNA is a universal requirement in trypanosomes; therefore, understanding transcription initiation at the SL RNA gene promoter is a crucial step toward understanding the control of tRNAP-II transcription in these parasites (4, 7).To date, components of the SL RNA transcriptional machinery have been studied by using genomics or biochemistry to identify candidate proteins followed by a combination of phenotypic analysis of protein function using either RNAi-silencing of endogenous protein in parasites or depletion/add back studies of in vitro transcription systems. T...

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Gene transcription in trypanosomes

Cited by 113 publications

References 47 publications

mRNA maturation by two-step trans-splicing/polyadenylation processing in trypanosomes

mRNA maturation by two-step trans-splicing/polyadenylation processing in trypanosomes

Regulatory elements involved in the post-transcriptional control of stage-specific gene expression in Trypanosoma cruzi: a review

Structure of the C-terminal domain of transcription factor IIB from Trypanosoma brucei

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