Cis-acting Regulatory Regions Research Articles

Genetic susceptibility to diabetic kidney disease is linked to promoter variants of XOR.

The lifetime risk of kidney disease in people with diabetes is 10-30%, implicating genetic predisposition in the cause of diabetic kidney disease (DKD). Here we identify an expression quantitative trait loci (QTLs) in the cis-acting regulatory region of the xanthine dehydrogenase, or xanthine oxidoreductase (Xor), a binding site for C/EBPβ, to be associated with diabetes-induced podocyte loss in DKD in male mice. We examine mouse inbred strains that are susceptible (DBA/2J) and resistant (C57BL/6J) to DKD, as well as a panel of recombinant inbred BXD mice, to map QTLs. We also uncover promoter XOR orthologue variants in humans associated with high risk of DKD. We introduced the risk variant into the 5'-regulatory region of XOR in DKD-resistant mice, which resulted in increased Xor activity associated with podocyte depletion, albuminuria, oxidative stress and damage restricted to the glomerular endothelium, which increase further with type 1 diabetes, high-fat diet and ageing. Therefore, differential regulation of Xor contributes to phenotypic consequences with diabetes and ageing.

Candida glabrata's Genome Plasticity Confers a Unique Pattern of Expressed Cell Wall Proteins.

Candida glabrata is the second most common cause of candidemia, and its ability to adhere to different host cell types, to microorganisms, and to medical devices are important virulence factors. Here, we consider three characteristics that confer extraordinary advantages to C. glabrata within the host. (1) C. glabrata has a large number of genes encoding for adhesins most of which are localized at subtelomeric regions. The number and sequence of these genes varies substantially depending on the strain, indicating that C. glabrata can tolerate high genomic plasticity; (2) The largest family of CWPs (cell wall proteins) is the EPA (epithelial adhesin) family of adhesins. Epa1 is the major adhesin and mediates adherence to epithelial, endothelial and immune cells. Several layers of regulation like subtelomeric silencing, cis-acting regulatory regions, activators, nutritional signaling, and stress conditions tightly regulate the expression of many adhesin-encoding genes in C. glabrata, while many others are not expressed. Importantly, there is a connection between acquired resistance to xenobiotics and increased adherence; (3) Other subfamilies of adhesins mediate adherence to Candida albicans, allowing C. glabrata to efficiently invade the oral epithelium and form robust biofilms. It is noteworthy that every C. glabrata strain analyzed presents a unique pattern of CWPs at the cell surface.

Nonradioactive Northern Blot Analysis to Detect Ebola Virus Minigenomic mRNA.

In this chapter, we describe the detection of Ebola virus minigenomic mRNA using a nonradioactive Northern hybridization. This protocol comprises all steps beginning with the synthesis of a digoxigenin-labeled riboprobe, harvest of transcribed mRNA from cells transfected with the Ebola virus minigenome system, separation of mRNA species by denaturing RNA gel electrophoresis, transfer of the mRNA to nylon membranes by vacuum blotting, and finally the detection of minigenome-specific mRNA through hybridization with a labeled riboprobe directed against the reporter gene.This method allows the direct study of cis-acting regulatory regions as well as trans-acting factors involved in Ebola virus minigenome transcription compared to the indirect measurement of reporter protein activity that additionally reflects translational effects (see Chapter 6 in this book for details).

Crispr Engineering in CD34+ Progenitors Reveals Cis-Acting Regulatory Regions Mediating 3D Interactions and Stem Cell Fate Decisions

DNA methylation is a critical regulator of cis-regulatory elements that can impact the distribution of epigenetic regulators and transcription factors. We have mapped DNA methylation changes in human CD34+ cells and downstream progeny to detect changes in DNA methylation with differentiation. Some large regions of low DNA methylation emerge with differentiation, which we call dynamic (d-) canyons. In order to determine whether these correlate with changes in the 3D genome, we generated 6 high-resolution Hi-C contact maps from CD34+CD38- cells, Adult bone marrow CD34+ cells, 7 days cultured CD34+ cells, CD71+CD36+CD235+ Erythroid cells, CD4+ T cells and AML patient blast cells. We generated ~ 1 billion mapped reads in order to create each 3D map of the genome at kilobase resolution. We identified several sites of d-canyons which correlate with changes in Hi-C loops. To study the functional role of d-canyons, we performed CRISPR/CAS9 mediated genome engineering targeting three sites of interest in CD34+ progenitors. We designed sgRNAs to delete several d-canyon regions that exhibited cell-type specific methylation and dynamic H3K27ac marking.First, we targeted a novel putative regulatory region of the RUNX1 gene, a critical master regulator of hematopoiesis that is frequently mutated in human leukemia. From genome-wide DNA methylation profiling, we identified a d-canyon located in the first intron of RUNX1, which overlaped with a H3K27ac peak in human CD34+CD38- hematopoietic progenitor cells. DNA methylation in this region is further depleted in T cells and increased in AML cells, suggesting a role for regulating RUNX1 in specific cell types. To study its function, we designed 2 sgRNAs to delete a 1.8 kb d-canyon. CRISPR/Cas9-mediated deletion of this region resulted in ablation of RUNX1 expression in cord blood hematopoietic stem cells and a significant decrease of engraftment activity in NSG mice along with an increase of erythroid colony forming ability in in vitro assays.In addition, we identified d-canyons upstream of the master regulators GATA2 and in the HOXA cluster. We deleted 1.7kb d-canyon upstream of GATA2 gene, finding that it resulted in increased self-renewal of CD34+CD38- cells in NSG xenografts. In contrast, when we deleted one a d-canyon located ~2Mb upstream of the HOXA cluster, within a HiC loop signal present only in CD34+CD38- cells, we observed in decreased CD34+CD38- cell self-renewal but a significant increase of CD34+CD38+ differentiated progenitors in an in vitro culture system, as well as in NSG mice. Colony forming assay showed decreased colony size and numbers.Finally, we identified a d-canyon associated with TCF3, also known as E2A, a transcription factor involved in B and T cell lineage differentiation. We designed 4 sgRNAs to delete 1.5kb d-canyon edge regions within the second intron of TCF3. Removal of this region resulted in a significant decrease of CD19+ B cells, but an increase of CD3+ T cells in NSG mice.Taken together, these results suggest the functional importance of d-canyons for orchestrating genome architecture and fate decisions of hematopoietic stem cells. These findings advance our understanding of the relationship between DNA methylation changes and loop interactions, providing new insights into the potential impact of potential aberrant DNA methylation and chromatin structure. DisclosuresNo relevant conflicts of interest to declare.

0411 Important lessons from complex genomes

The approximately three billion base pairs of the human DNA represent a storage devise encoding information for hundreds of thousands of processes that can go on within and outside of a human cell. This information is revealed in the RNAs that are composed of 12 billion nucleotides considering the strandedness and the allelic content each of the diploid copies of the genome. Results stemming from the efforts to catalog and analyze the RNA products made by cells in the human (ENCODE), fly-worm (modENCODE) and mouse ENCODE projects have shed light on both the functional content and how this information is organized by various genomes. In human cells, a total of ∼161,000 transcripts present within ∼50,000 genic regions represent our previously best manually-curated annotation (based on v 7 Gencode) of the transcriptome. The results from the ENCODE project point to considerable supplementation of these data. Analyses of these transcriptome data sets have resulted in important and under appreciated lessons such as: (1) pervasive genome-wide transcription prompts a need to redefine the definition of a gene, (2) expression ranges follow transcript types and subcellular localization, (3) expression of isoforms of a gene by a cell do not follow a minimalistic strategy, and (4) genomic characteristics of potential trans-acting enhancer regions are distinguishable from other types of cis-acting regulatory regions. These and other lessons drawn from the landscape of both coding and non-coding RNAs present in eukaryotic cells have been used to assist in understanding and organizing what is often seen as dauntingly complex genomes.

Persistent Alterations in Microglial Enhancers in a Model of Chronic Pain.

Chronic pain is a common and devastating condition that induces well-characterized changes in neurons and microglia. One major unanswered question is why these changes should persist long after the precipitating injury has healed. Here, we suggest that some of the longer-lasting consequences of nerve injury may be hidden in the epigenome. Cell sorting and sequencing techniques were used to characterize the spinal cord immune response in a mouse model of chronic neuropathic pain. Infiltration of peripheral myeloid cells was found to be absent, and RNA sequencing (RNA-seq) of central microglia revealed transient gene expression changes in response to nerve ligation. Conversely, examination of microglial enhancers revealed persistent, post-injury alterations in close proximity to transcriptionally regulated genes. Enhancers are regions of open chromatin that define a cell's transcription factor binding profile. We hypothesize that changes at enhancers may constitute a mechanism by which painful experiences are recorded at a molecular level.

Cis-Regulatory Elements Determine Germline Specificity and Expression Level of an Isopentenyltransferase Gene in Sperm Cells of Arabidopsis

Flowering plant sperm cells transcribe a divergent and complex complement of genes. To examine promoter function, we chose an isopentenyltransferase gene known as PzIPT1. This gene is highly selectively transcribed in one sperm cell morphotype of Plumbago zeylanica, which preferentially fuses with the central cell during fertilization and is thus a founding cell of the primary endosperm. In transgenic Arabidopsis (Arabidopsis thaliana), PzIPT1 promoter displays activity in both sperm cells and upon progressive promoter truncation from the 5'-end results in a progressive decrease in reporter production, consistent with occurrence of multiple enhancer sites. Cytokinin-dependent protein binding motifs are identified in the promoter sequence, which respond with stimulation by cytokinin. Expression of PzIPT1 promoter in sperm cells confers specificity independently of previously reported Germline Restrictive Silencer Factor binding sequence. Instead, a cis-acting regulatory region consisting of two duplicated 6-bp Male Gamete Selective Activation (MGSA) motifs occurs near the site of transcription initiation. Disruption of this sequence-specific site inactivates expression of a GFP reporter gene in sperm cells. Multiple copies of the MGSA motif fused with the minimal CaMV35S promoter elements confer reporter gene expression in sperm cells. Similar duplicated MGSA motifs are also identified from promoter sequences of sperm cell-expressed genes in Arabidopsis, suggesting selective activation is possibly a common mechanism for regulation of gene expression in sperm cells of flowering plants.

Studying RNA-binding protein interactions with target mRNAs in eukaryotic cells: native ribonucleoprotein immunoprecipitation (RIP) assays.

Post-transcriptional regulation of mRNA can potently dictate protein expression patterns in eukaryotic cells. This mode of regulation occurs through cis-acting regulatory regions in the mRNA transcript that mediate direct interactions with trans-acting RNA-binding proteins (RBPs). This mRNA/protein interaction can be studied in numerous ways that range from in vitro to in vivo through messenger ribonucleoprotein immunoprecipitation (mRNP-IP or RIP) assays. This modified immunoprecipitation approach is an important and sensitive method to determine the regulation of gene expression by specific RBPs under different cellular stressors.

Identification of DNA methylation changes at cis-regulatory elements during early steps of HSC differentiation using tagmentation-based whole genome bisulfite sequencing

Epigenetic alterations during cellular differentiation are a key molecular mechanism which both instructs and reinforces the process of lineage commitment. Within the haematopoietic system, progressive changes in the DNA methylome of haematopoietic stem cells (HSCs) are essential for the effective production of mature blood cells. Inhibition or loss of function of the cellular DNA methylation machinery has been shown to lead to a severe perturbation in blood production and is also an important driver of malignant transformation. HSCs constitute a very rare cell population in the bone marrow, capable of life-long self-renewal and multi-lineage differentiation. The low abundance of HSCs has been a major technological barrier to the global analysis of the CpG methylation status within both HSCs and their immediate progeny, the multipotent progenitors (MPPs). Within this Extra View article, we review the current understanding of how the DNA methylome regulates normal and malignant hematopoiesis. We also discuss the current methodologies that are available for interrogating the DNA methylation status of HSCs and MPPs and describe a new data set that was generated using tagmentation-based whole genome bisulfite sequencing (TWGBS) in order to comprehensively map methylated cytosines using the limited amount of genomic DNA that can be harvested from rare cell populations. Extended analysis of this data set clearly demonstrates the added value of genome-wide sequencing of methylated cytosines and identifies novel important cis-acting regulatory regions that are dynamically remodeled during the first steps of haematopoietic differentiation.

LIN-42, the Caenorhabditis elegans PERIOD homolog, negatively regulates microRNA transcription.

During C. elegans development, microRNAs (miRNAs) function as molecular switches that define temporal gene expression and cell lineage patterns in a dosage-dependent manner. It is critical, therefore, that the expression of miRNAs be tightly regulated so that target mRNA expression is properly controlled. The molecular mechanisms that function to optimize or control miRNA levels during development are unknown. Here we find that mutations in lin-42, the C. elegans homolog of the circadian-related period gene, suppress multiple dosage-dependent miRNA phenotypes including those involved in developmental timing and neuronal cell fate determination. Analysis of mature miRNA levels in lin-42 mutants indicates that lin-42 functions to attenuate miRNA expression. Through the analysis of transcriptional reporters, we show that the upstream cis-acting regulatory regions of several miRNA genes are sufficient to promote highly dynamic transcription that is coupled to the molting cycles of post-embryonic development. Immunoprecipitation of LIN-42 complexes indicates that LIN-42 binds the putative cis-regulatory regions of both non-coding and protein-coding genes and likely plays a role in regulating their transcription. Consistent with this hypothesis, analysis of miRNA transcriptional reporters in lin-42 mutants indicates that lin-42 regulates miRNA transcription. Surprisingly, strong loss-of-function mutations in lin-42 do not abolish the oscillatory expression patterns of lin-4 and let-7 transcription but lead to increased expression of these genes. We propose that lin-42 functions to negatively regulate the transcriptional output of multiple miRNAs and mRNAs and therefore coordinates the expression levels of genes that dictate temporal cell fate with other regulatory programs that promote rhythmic gene expression.

Ftx is dispensable for imprinted X-chromosome inactivation in preimplantation mouse embryos.

X-chromosome inactivation (XCI) equalizes gene expression between the sexes by inactivating one of the two X chromosomes in female mammals. Xist has been considered as a major cis-acting factor that inactivates the paternally derived X chromosome (Xp) in preimplantation mouse embryos (imprinted XCI). Ftx has been proposed as a positive regulator of Xist. However, the physiological role of Ftx in female animals has never been studied. We recently reported that Ftx is located in the cis-acting regulatory region of the imprinted XCI and expressed from the inactive Xp, suggesting a role in the imprinted XCI mechanism. Here we examined the effects on imprinted XCI using targeted deletion of Ftx. Disruption of Ftx did not affect the survival of female embryos or expression of Xist and other X-linked genes in the preimplantation female embryos. Our results indicate that Ftx is dispensable for imprinted XCI in preimplantation embryos.

Novel aspects of RNA regulation in Staphylococcus aureus.

A plethora of RNAs with regulatory functions has been discovered in many non-pathogenic and pathogenic bacteria. In Staphylococcus aureus, recent findings show that a large variety of RNAs control target gene expression by diverse mechanisms and many of them are expressed in response to specific internal or external signals. These RNAs comprise trans-acting RNAs, which regulate gene expression through binding with mRNAs, and cis-acting regulatory regions of mRNAs. Some of them possess multiple functions and encode small but functional peptides. In this review, we will present several examples of RNAs regulating pathogenesis, antibiotic resistance, and host-pathogen interactions and will illustrate how regulatory proteins and RNAs form complex regulatory circuits to express the virulence factors in a dynamic manner.

Identification of an Imprinted Gene Cluster in the X-Inactivation Center

Mammalian development is strongly influenced by the epigenetic phenomenon called genomic imprinting, in which either the paternal or the maternal allele of imprinted genes is expressed. Paternally expressed Xist, an imprinted gene, has been considered as a single cis-acting factor to inactivate the paternally inherited X chromosome (Xp) in preimplantation mouse embryos. This means that X-chromosome inactivation also entails gene imprinting at a very early developmental stage. However, the precise mechanism of imprinted X-chromosome inactivation remains unknown and there is little information about imprinted genes on X chromosomes. In this study, we examined whether there are other imprinted genes than Xist expressed from the inactive paternal X chromosome and expressed in female embryos at the preimplantation stage. We focused on small RNAs and compared their expression patterns between sexes by tagging the female X chromosome with green fluorescent protein. As a result, we identified two micro (mi)RNAs–miR-374-5p and miR-421-3p–mapped adjacent to Xist that were predominantly expressed in female blastocysts. Allelic expression analysis revealed that these miRNAs were indeed imprinted and expressed from the Xp. Further analysis of the imprinting status of adjacent locus led to the discovery of a large cluster of imprinted genes expressed from the Xp: Jpx, Ftx and Zcchc13. To our knowledge, this is the first identified cluster of imprinted genes in the cis-acting regulatory region termed the X-inactivation center. This finding may help in understanding the molecular mechanisms regulating imprinted X-chromosome inactivation during early mammalian development.

FGF signalling inhibition in ESCs drives rapid genome-wide demethylation to the epigenetic ground state of pluripotency

Genome-wide erasure of DNA methylation takes place in primordial germ cells (PGCs) and early embryos and is linked with pluripotency. Inhibition of Erk1/2 and Gsk3β signalling in mouse embryonic stem cells (ESCs) by small molecule inhibitors (called 2i) has recently been shown to induce hypomethylation. We show by whole-genome bisulphite sequencing that 2i induces rapid and genome-wide demethylation on a scale and pattern similar to that in migratory PGCs and early embryos. Major satellites, intracisternal A particles (IAPs) and imprinted genes remain relatively resistant to erasure. Demethylation involves oxidation of 5-methylcytosine (5mC) to 5-hydroxymethylcytosine (5hmC), impaired maintenance of 5mC and 5hmC and repression of the de novo methyltransferases (Dnmt3a, Dnmt3b) and Dnmt3L. We identify a Prdm14 and Nanog binding cis-acting regulatory region in Dnmt3b that is highly responsive to signalling. These insights provide a novel framework for understanding how signalling pathways regulate reprogramming to an epigenetic ground state of pluripotency.

FGF Signaling Inhibition in ESCs Drives Rapid Genome-wide Demethylation to the Epigenetic Ground State of Pluripotency

SummaryGenome-wide erasure of DNA methylation takes place in primordial germ cells (PGCs) and early embryos and is linked with pluripotency. Inhibition of Erk1/2 and Gsk3β signaling in mouse embryonic stem cells (ESCs) by small-molecule inhibitors (called 2i) has recently been shown to induce hypomethylation. We show by whole-genome bisulphite sequencing that 2i induces rapid and genome-wide demethylation on a scale and pattern similar to that in migratory PGCs and early embryos. Major satellites, intracisternal A particles (IAPs), and imprinted genes remain relatively resistant to erasure. Demethylation involves oxidation of 5-methylcytosine (5mC) to 5-hydroxymethylcytosine (5hmC), impaired maintenance of 5mC and 5hmC, and repression of the de novo methyltransferases (Dnmt3a and Dnmt3b) and Dnmt3L. We identify a Prdm14- and Nanog-binding cis-acting regulatory region in Dnmt3b that is highly responsive to signaling. These insights provide a framework for understanding how signaling pathways regulate reprogramming to an epigenetic ground state of pluripotency.

Silencing of a large microRNA cluster on human chromosome 14q32 in melanoma: biological effects of mir-376a and mir-376c on insulin growth factor 1 receptor

BackgroundMetastatic melanoma is a devastating disease with limited therapeutic options. MicroRNAs (miRNAs) are small non coding RNA molecules with important roles in post-transcriptional gene expression regulation, whose aberrant expression has been implicated in cancer.ResultsWe show that the expression of miRNAs from a large cluster on human chromosome 14q32 is significantly down-regulated in melanoma cell lines, benign nevi and melanoma samples relative to normal melanocytes. This miRNA cluster resides within a parentally imprinted chromosomal region known to be important in development and differentiation. In some melanoma cell lines, a chromosomal deletion or loss-of-heterozygosity was observed in the cis-acting regulatory region of this cluster. In several cell lines we were able to re-express two maternally-induced genes and several miRNAs from the cluster with a combination of de-methylating agents and histone de-acetylase inhibitors, suggesting that epigenetic modifications take part in their silencing. Stable over-expression of mir-376a and mir-376c, two miRNAs from this cluster that could be re-expressed following epigenetic manipulation, led to modest growth retardation and to a significant decrease in migration in-vitro. Bioinformatic analysis predicted that both miRNAs could potentially target the 3'UTR of IGF1R. Indeed, stable expression of mir-376a and mir-376c in melanoma cells led to a decrease in IGF1R mRNA and protein, and a luciferase reporter assay indicated that the 3'UTR of IGF1R is a target of both mir-376a and mir-376c.ConclusionsOur work is the first to show that the large miRNA cluster on chromosome 14q32 is silenced in melanoma. Our results suggest that down-regulation of mir-376a and mir-376c may contribute to IGF1R over-expression and to aberrant negative regulation of this signaling pathway in melanoma, thus promoting tumorigenesis and metastasis.

The Arabidopsis CORI3 promoter contains two cis-acting regulatory regions required for transcriptional activity in companion cells

Companion cells are metabolically active and functionally specialized cells that behave as terminals for the transport of materials between phloem and the surrounding tissue. Although previous research has clarified the distinct function of companion cells, it is still largely unknown how plants establish and maintain the special identity of these cells. To shed further light on this issue, we carried out expressed sequence tag (EST) analysis. To minimize the difficulty of dissociating and gathering intact companion cells, vascular strings with an abundant content of companion cells were excised from the petioles of Brassica napus. By random sequencing with a string-specific cDNA library derived by suppression subtractive hybridization between the string itself and the petiole from which it had been removed, we identified 377 ESTs and assembled them into 247 EST groups. The most frequent EST was ExBdl-102 (15 of 377 ESTs), which showed the highest sequence similarity to the Arabidopsis CORI3 (CORONATINE INDUCED 3) gene. The CORI3 promoter:GUS showed predominant expression in the vascular tissue of Arabidopsis. Through transient expression assay using Brassica vasculature and gene-gun-mediated transient assay, we found two integrated cis-regulatory regions of the CORI3 promoter. This work has provided not only string-specific EST information and shown that two novel cis-regulatory regions sustain transcriptional activity in companion cells, but also a series of procedures for efficiently examining the transcriptional framework of companion cells by exploiting the histochemical advantage of B. napus as an experimental material.

Polypyrimidine tract-binding protein is required for the repression of gene expression by all-trans retinoic acid

All-trans retinoic acid is a key regulator of early development. High concentrations of retinoic acid interfere with differentiation and migration of neural crest cells. Here we report that a dinucleotide repeat in the cis-element of Snail2 (previously known as Slug) gene plays a role in repression by all-trans retinoic acid. We analyzed the cis-acting regulatory regions of the Xenopus Snail2 gene, whose expression is repressed by all-trans retinoic acid. The analysis identified a TG/CA repeat as a necessary element for the repression. By performing a yeast one-hybrid screen, we found that a polypyrimidine tract-binding protein (PTB), which is known to be a regulator of the alternative splicing of pre-messenger RNA, binds to the TG/CA repeat. Overexpression and knockdown experiments for PTB in HEK293 cells and Xenopus embryos indicated that PTB is required for repression by retinoic acid. The green fluorescent protein-PTB fusion protein was localized in the nucleus of 293T cells. In situ hybridization for PTB in Xenopus embryos showed that PTB is expressed at the regions including neural crest at the early stages. Our results indicate that PTB plays a role in the repression of gene expression by retinoic acid through binding to the TG/CA repeats.

Abstract A17: miRNA silencing in malignant melanoma: Mechanisms, regulation, and potential implications

Abstract Metastatic melanoma is a devastating disease with limited treatment options. miRNAs are small RNA species within cells whose aberrant expression has been implicated in cancerous transformation, in some cases by a mechanism of cellular de-differentiation. The role of miRNA in melanoma is still not known. We recently observed that the expression of miRNAs from a large intergenic miRNA cluster is significantly down-regulated or absent in melanoma cell lines in comparison to normal melanocytes. This cluster resides within a parentally imprinted chromosomal region implicated in development and differentiation, and the miRNAs in this region are normally expressed selectively only in brain and skin. This chromosomal region was shown to be involved in the pathogenesis of ovarian carcinoma, and several of the miRNAs within it were shown to have tumor suppressor functions in other cellular models. Our results demonstrate that in some melanoma cell lines, there is a chromosomal deletion or loss of heterozygosity in the cis-acting differentially-methylated regulatory region of this cluster. Conversely, in other cell lines we were able to re-express some of these miRNAs using epigenetic modifiers (de-methylating agents and histone de-acetylase inhibitors), suggesting that epigenetic aberrations take part in their silencing. We are now assessing whether miRNA re-expression or ectopic expression decreases the tumorigenic and metastatic potential of melanoma cells. Our results suggest that aberrant regulation of this chromosomal region has a role in the pathogenesis of melanoma, and may even lead, in the future, to the development of new therapeutic strategies and bio-markers in this yet incurable disease. Citation Information: Clin Cancer Res 2010;16(7 Suppl):A17

A var gene promoter implicated in severe malaria nucleates silencing and is regulated by 3′ untranslated region and intronic cis-elements

Questions surround the mechanism of mutually exclusive expression by which Plasmodium falciparum mediates activation and silencing of var genes. These encode PfEMP1 proteins, which function as cytoadherent and immunomodulatory molecules at the surface of parasitised erythrocytes. Current evidence suggests that promoter silencing by var introns might play a key role in var gene regulation. To evaluate the impact of cis-acting regulatory regions on var silencing, we generated P. falciparum lines in which luciferase was placed under the control of an UpsA var promoter. By utilising the Bxb1 integrase system, these reporter cassettes were targeted to a genomic region that was not in apposition to var subtelomeric domains. This eliminated possible effects from surrounding telomeric elements and removed the variability inherent in episomal systems. Studies with highly synchronised parasites revealed that the UpsA element possessed minimal activity in comparison with a heterologous ( hrp3) promoter. This may result from the integrated UpsA promoter being largely silenced by the neighbouring cg6 promoter. Our analyses also revealed that the DownsA 3′ untranslated region further decreased the luciferase activity from both cassettes, whereas the var A intron repressed the UpsA promoter specifically. By applying multivariate analysis over the entire cell cycle, we confirmed the significance of these cis-elements and found the parasite stage to be the major factor regulating UpsA-promoter activity. Additionally, we observed that the UpsA promoter was capable of nucleating reversible silencing that spread to a downstream promoter. We believe these studies are the first to analyse promoter activity of Group A var genes, which have been implicated in severe malaria, and support the model that var introns can further suppress var expression. These data also suggest an important suppressive role for the DownsA terminator. Our findings imply the existence of multiple levels of var gene regulation in addition to intrinsic promoter-dependent silencing.