5′ flanking region of var genes nucleate histone modification patterns linked to phenotypic inheritance of virulence traits in malaria parasites

In the human malaria parasite Plasmodium falciparum antigenic variation facilitates long-term chronic infection of the host. This is achieved by sequential expression of a single member of the 60-member var family. Here we show that the 5′ flanking region nucleates epigenetic events strongly linked to the maintenance of mono-allelic var gene expression pattern during parasite proliferation. Tri- and dimethylation of histone H3 lysine 4 peak in the 5′ upstream region of transcribed var and during the poised state (non-transcribed phase of var genes during the 48 h asexual life cycle), ‘bookmarking’ this member for re-activation at the onset of the next cycle. Histone H3 lysine 9 trimethylation acts as an antagonist to lysine 4 methylation to establish stably silent var gene states along the 5′ flanking and coding region. Furthermore, we show that competition exists between H3K9 methylation and H3K9 acetylation in the 5′ flanking region and that these marks contribute epigenetically to repressing or activating var gene expression. Our work points to a pivotal role of the histone methyl mark writing and reading machinery in the phenotypic inheritance of virulence traits in the malaria parasite

Telomeric Heterochromatin Propagation and Histone Acetylation Control Mutually Exclusive Expression of Antigenic Variation Genes in Malaria Parasites

SummaryMalaria parasites use antigenic variation to avoid immune clearance and increase the duration of infection in the human host. Variation at the surface of P. falciparum-infected erythrocytes is mediated by the differential control of a family of surface antigens encoded by var genes. Switching of var gene expression occurs in situ, mostly from telomere-associated loci, without detectable DNA alterations, suggesting that it is controlled by chromatin structure. We have identified chromatin modifications at telomeres that spread far into telomere-proximal regions, including var gene loci (>50 kb). One type of modification is mediated by a protein homologous to yeast Sir2 called PfSir2, which forms a chromosomal gradient of heterochromatin structure and histone hypoacetylation. Upon activation of a specific telomere-associated var gene, PfSir2 is removed from the promoter region and acetylation of histone occurs. Our data demonstrate that mutually exclusive transcription of var genes is linked to the dynamic remodeling of chromatin

KRas4BG12C/D/PDE6δ Heterodimeric Molecular Complex: A Target Molecular Multicomplex for the Identification and Evaluation of Nontoxic Pharmacological Compounds for the Treatment of Pancreatic Cancer

The search for new targeted therapies to improve the quality of life of patients with pancreatic cancer has taken about 30 years. Compounds that can inhibit the K-Ras4B oncoprotein signaling pathway have been sought. Taking into account that the interaction of KRas4B with PDE6δ is essential for its transport and subsequent activation in the plasma membrane, our working group identified and evaluated in vitro and in vivo small organic molecules that could act as molecular staples to stabilize the KRas4B/PDE6δ heterodimeric complex. From this group of molecules, 38 compounds with high interaction energies on the structure of the crystallized molecular complex were selected, indicating that they efficiently stabilized the molecular complex. In vitro evaluation of compounds called D14, C22, and C19 showed significant specific effects on the cell viability of pancreatic cancer cells (and not on normal cells), thus inducing death by apoptosis and significantly inhibiting the activation of the pathways, signaling AKT and ERK. In addition to these experimental findings, we were also able to detect that compounds D14 and C22 showed significant tumor growth inhibitory activity in pancreatic cancer cell-induced subcutaneous xenograft models

PfAlbas constitute a new eukaryotic DNA/RNA-binding protein family in malaria parasites

In Plasmodium falciparum, perinuclear subtelomeric chromatin conveys monoallelic expression of virulence genes. However, proteins that directly bind to chromosome ends are poorly described. Here we identify a novel DNA/RNA-binding protein family that bears homology to the archaeal protein Alba (Acetylation lowers binding affinity). We isolated three of the four PfAlba paralogs as part of a molecular complex that is associated with the P. falciparum-specific TARE6 (Telomere-Associated Repetitive Elements 6) subtelomeric region and showed in electromobility shift assays (EMSAs) that the PfAlbas bind to TARE6 repeats. In early blood stages, the PfAlba proteins were enriched at the nuclear periphery and partially co-localized with PfSir2, a TARE6-associated histone deacetylase linked to the process of antigenic variation. The nuclear location changed at the onset of parasite proliferation (trophozoite-schizont), where the PfAlba proteins were also detectable in the cytoplasm in a punctate pattern. Using single-stranded RNA (ssRNA) probes in EMSAs, we found that PfAlbas bind to ssRNA, albeit with different binding preferences. We demonstrate for the first time in eukaryotes that Alba-like proteins bind to both DNA and RNA and that their intracellular location is developmentally regulated. Discovery of the PfAlbas may provide a link between the previously described subtelomeric non-coding RNA and the regulation of antigenic variation

Characterisation of PfSec61, a Plasmodium falciparum homologue of a component of the translocation machinery at the endoplasmic reticulum membrane of eukaryotic cells1Note: nucleotide sequence data reported in this paper is available in the Genbank™ database under the accession number AF006204.1

International audiencePlasmodium falciparum secretes several proteins that cause changes in the erythrocyte membrane enabling it to survive within red blood cells. Little is known of the mechanisms involved in the secretion and targeting of parasite polypeptides to the various cell compartments. The P. falciparum gene homologous to the mammalian Sec61alpha, gene, which encodes a component of the translocation pore in the endoplasmic reticulum of eukaryotic cells, was characterised to investigate the translocation process in the parasite. PfSec61 is present as a unique copy in the parasite genome and was mapped to chromosome 13. It encodes a 40 kDa polypeptide, as shown by immunoblotting and immunoprecipitation of [35S]methionine metabolically-labelled parasite extracts. The deduced amino acid sequence of PfSec61 is 87% similar to the mammalian polypeptide, and the two proteins give similar hydropathy plots. These results strongly suggest that PfSec61 has the same topological orientation and functional role as Sec61alpha. Anti-PfSec61 antibodies were used to investigate the cellular location and kinetics of expression of the polypeptide in the parasite. Immunofluorescence confocal microscopy showed that PfSec61 was located in the parasite cytoplasm, close to the nucleus, in a position consistent with its being in the endoplasmic reticulum

Telomeric Heterochromatin in Plasmodium falciparum

Until very recently, little was known about the chromatin structure of the telomeres and subtelomeric regions in Plasmodium falciparum. In yeast and Drosophila melanogaster, chromatin structure has long been known to be an important aspect in the regulation and functioning of these regions. Telomeres and subtelomeric regions are enriched in epigenetic marks that are specific to heterochromatin, such as methylation of lysine 9 of histone H3 and lysine 20 of histone H4. In P. falciparum, histone modifications and the presence of both the heterochromatin “writing” (PfSir2, PKMT) and “reading” (PfHP1) machinery at telomeric and subtelomeric regions indicate that these regions are likely to have heterochromatic structure that is epigenetically regulated. This structure may be important for telomere functions such as the silencing of the var gene family implicated in the cytoadherence and antigenic variation of these parasites

Natural-geographic characteristics of Bjelovar-bilogora County in the function of tourism development

Bjelovarsko-bilogorska županija smještena je u Središnjoj hrvatskoj zavali te ima povoljne prirodnogeografske uvjete za razvoj turizma. Županija ima dobar geoprometni položaj prema najvećoj urbanoj aglomeraciji koja je ujedno i najveće turističko središte kontinentalne Hrvatske. Usprkos bogatoj i raznolikoj prirodnogeografskoj samo je zdravstveno-lječilišni turizam sustavno razvijan od druge polovice 20. stoljeća, a sve veća važnost pridaje se lovnom i ruralnom turizmu. Za potrebe istraživanja provedeno je kvantitativno anketno istraživanje na neprobabilistički odabranom, prigodnom uzorku koji čine građani Republike Hrvatske sa stalnim prebivalištem na području Bjelovarsko-bilogorske županije i oni koji nemaju stalno prebivalište na području Bjelovarsko-bilogorske županije. Na temelju rezultata ankete i analize statističkih podataka utvrđeno je da su posjetitelji uglavnom zadovoljni cjelokupnom turističkom ponudom, no nedostaje im više manifestacija i zabavnih sadržaja. Budući razvoj turizma Bjelovarsko-bilogorske županije trebao bi se temeljiti na nadopuni postojeće turističke ponude koja ima brojne neiskorištene prirodne potencijale, te što boljom promocijom istih.Bjelovar-bilogora County is located in central Croatian basin and has favourable natural-geographical conditions for the tourism development. County has a good geographic position towards the largest urban agglomeration in Croatia, which is also the largest source of domestic travel demand. Despite its rich and diverse natural resource basis, only medical and health tourism has been systematically developed, while the increasing importance is given to hunting and rural tourism. For the purpose of this study quantitative survey on a nonprobabilistic sample consisting of Croatian citizens who have permanent residence in the area of Bjelovar County and others who have not, was conducted. Visitors are mostly satisfied with the overall tourist offer, but they have expressed a desire for a larger number of cultural and entertainment events. Further development of tourism in Bjelovar-bilogora County should be based on the upgrading and better promotion of the existing touristic offer that has many unexploited natural resources

Separation and Mapping of Chromosomes of Parasitic Protozoa

Many protozoan parasites represent an important group of human pathogens. Pulsed Field Gradient Gel Electrophoresis (PFGE) analysis has been an important tool for fundamental genetic studies of parasites like Trypanosoma, Leishmania, Giardia or the human malaria parasite Plasmodium falciparum. We present PFGE conditions allowing a high resolution separation of chromosomes ranging from 500 to 4000 kb within a two day electrophoresis run. In addition, we present conditions for separating large chromosomes (2000-6000 kb) within 36 hr. We demontrate that the application of two dimentional PFGE (2D-PFGE) technique to parasite karyotypes is a very useful method for the analysis of dispersed gene families and comparative studies of the intrachomosomal genome organizatio

5′ flanking region of genes nucleate histone modification patterns linked to phenotypic inheritance of virulence traits in malaria parasites-3

<p><b>Copyright information:</b></p><p>Taken from "5′ flanking region of genes nucleate histone modification patterns linked to phenotypic inheritance of virulence traits in malaria parasites"</p><p></p><p>Molecular Microbiology 2007;66(6):1296-1305.</p><p>Published online 19 Nov 2007</p><p>PMCID:PMC2228885.</p><p>© 2007 The Authors Journal compilation © 2007 Blackwell Publishing Ltd</p