Small RNAs with 5′-Polyphosphate Termini Associate with a Piwi-Related Protein and Regulate Gene Expression in the Single-Celled Eukaryote Entamoeba histolytica

Small interfering RNAs regulate gene expression in diverse biological processes, including heterochromatin formation and DNA elimination, developmental regulation, and cell differentiation. In the single-celled eukaryote Entamoeba histolytica, we have identified a population of small RNAs of 27 nt size that (i) have 5′-polyphosphate termini, (ii) map antisense to genes, and (iii) associate with an E. histolytica Piwi-related protein. Whole genome microarray expression analysis revealed that essentially all genes to which antisense small RNAs map were not expressed under trophozoite conditions, the parasite stage from which the small RNAs were cloned. However, a number of these genes were expressed in other E. histolytica strains with an inverse correlation between small RNA and gene expression level, suggesting that these small RNAs mediate silencing of the cognate gene. Overall, our results demonstrate that E. histolytica has an abundant 27 nt small RNA population, with features similar to secondary siRNAs from C. elegans, and which appear to regulate gene expression. These data indicate that a silencing pathway mediated by 5′-polyphosphate siRNAs extends to single-celled eukaryotic organisms

Short hairpin RNA-mediated knockdown of protein expression in Entamoeba histolytica

<p>Abstract</p> <p>Background</p> <p><it>Entamoeba histolytica </it>is an intestinal protozoan parasite of humans. The genome has been sequenced, but the study of individual gene products has been hampered by the lack of the ability to generate gene knockouts. We chose to test the use of RNA interference to knock down gene expression in <it>Entamoeba histolytica</it>.</p> <p>Results</p> <p>An episomal vector-based system, using the <it>E. histolytica </it>U6 promoter to drive expression of 29-basepair short hairpin RNAs, was developed to target protein-encoding genes in <it>E. histolytica</it>. The short hairpin RNAs successfully knocked down protein levels of all three unrelated genes tested with this system: Igl, the intermediate subunit of the galactose- and N-acetyl-D-galactosamine-inhibitable lectin; the transcription factor URE3-BP; and the membrane binding protein EhC2A. Igl levels were reduced by 72%, URE3-BP by 89%, and EhC2A by 97%.</p> <p>Conclusion</p> <p>Use of the U6 promoter to drive expression of 29-basepair short hairpin RNAs is effective at knocking down protein expression for unrelated genes in <it>Entamoeba histolytica</it>, providing a useful tool for the study of this parasite.</p

Calcium-dependent protein kinase 1 is an essential regulator of exocytosis in Toxoplasma

Calcium-regulated exocytosis is a ubiquitous process in eukaryotes, whereby secretory vesicles fuse with the plasma membrane and release their contents in response to an intracellular calcium surge1. This process regulates diverse cellular functions like plasma membrane repair in plants and animals2,3, discharge of defensive spikes in Paramecium4, and secretion of insulin from pancreatic cells, immune modulators from lymphocytes, and chemical transmitters from neurons5. In animal cells, serine/threonine kinases including PKA, PKC and CaM-kinases have been implicated in calcium-signal transduction leading to regulated secretion1,6,7. Although plants and protozoa also regulate secretion via intracellular calcium, the means by which these signals are relayed have not been elucidated. Here we demonstrate that the Toxoplasma gondii calcium-dependent protein kinase 1 (TgCDPK1) is an essential regulator of calcium-dependent exocytosis in this opportunistic human pathogen. Conditional suppression of TgCDPK1 revealed that it controls calcium-dependent secretion of specialized organelles called micronemes, resulting in a block of essential phenotypes including parasite motility, host-cell invasion, and egress. This phenotype was recapitulated using a chemical biology approach, wherein pyrazolopyrimidine-derived compounds specifically inhibited TgCDPK1 and disrupted the parasite life cycle at stages dependent on microneme secretion. Inhibition was specific to TgCDPK1, since expression of a resistant kinase mutant reversed sensitivity to the inhibitor. TgCDPK1 is conserved among apicomplexans and belongs to a family of kinases shared with plants and ciliates8, suggesting that related CDPKs may play a role in calcium-regulated secretion in other organisms. Since this kinase family is absent from mammalian hosts, it represents a validated target that may be exploitable for chemotherapy against T. gondii and related apicomplexans

Factors associated with lamotrigine concentration/dose ratio in individuals with bipolar disorders

International audienceMonitoring of lamotrigine levels is recommended in epilepsy. However, in bipolar disorders (BD), no study has described the therapeutic range in daily practice and factors being associated to it. We used retrospective data of individuals with BD, treated with lamotrigine, and included in the FondaMental Advanced Centers of Expertise for Bipolar Disorders cohort. We extracted clinical and biological data and explored associations between these variables and lamotrigine concentration/dose (C/D) ratio. The database included 675 individuals who received lamotrigine at inclusion, whose main characteristics were female sex (68.3%) and BD type 2 (52.1%). Data about lamotrigine C/D ratio were available for 205 individuals. Lamotrigine C/D ratio was significantly associated with: Body Mass Index (BMI) (r=-0.159), estimated GFR (glomerular filtration rate) (r=-0.228), total bilirubin (r = 0.241) and at a trend level, antidepressant co-prescription (U = 3169). The model obtained was: lamotrigine C/D ratio = 1.736 - 0.013*BMI + 0.095*total bilirubin (UI/L) - 0.007*eGFR (ml/min) + 0.210*AST/ALT – 0.004*GGT (UI/L) + 0.014*age (year) + 0.303*currently smoking (yes or no) – 0.588*antidepressant co-prescription (yes or no) – 0.357*gender (F = 1.899, p = 0.057, adjusted R2 = 0.11) Information about plasma lamotrigine C/D ratio were available for only 205 out of the 675 individuals in the database and has been obtained from different laboratories. The representativeness of the included sample may be questionable. This is the first study providing information on a large sample of individuals with BD regarding factors associated with lamotrigine C/D ratio. This study allows to propose a model of lamotrigine C/D ratio that would deserve further replication