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The MIR396 family, composed of ath-miR396a and ath-miR396b in Arabidopsis, is conserved among plant species and is known to target the Growth-Regulating Factor ( GRF) gene family. ath-miR396 overexpressors or grf mutants are characterised by small and narrow leaves and show embryogenic defects such as cotyledon fusion. Heterologous expression of ath-miR396a has been reported in tobacco and resulted in reduction of the expression of three Nt GRF genes. In this study, the precursor of the Populus trichocarpa ptc-miR396c, with a mature sequence identical to ath-miR396b, was expressed under control of the Ca MV35S promoter in tobacco. Typical phenotypes of GRF down-regulation were observed, including cotyledon fusion and lack of shoot apical meristem ( SAM). At later stage of growth, transgenic plants had delayed development and altered specification of organ type during flower development. The third and fourth whorls of floral organs were modified into stigmatoid anthers and fasciated carpels, respectively. Several Nt GRF genes containing a miR396 binding site were found to be down-regulated, and the cleavage of their corresponding m RNA at the miR396 binding site was confirmed for two of them using RACE- PCR analysis. The data obtained agree with the functional conservation of the miR396 family in plants and suggest a role for the miR396/ GRF network in determination of floral organ specification. [ABSTRACT FROM AUTHOR]

Sphaeropsidins are iso-pimarane diterpenes produced by phytopathogenic fungi that display promising anticancer activities. Sphaeropsidin A, in particular, has been shown to counteract regulatory volume increase, a process used by cancer cells to avoid apoptosis. This study reports the hemi-synthesis of new lipophilic derivatives obtained by modifications of the C15,C16-alkene moiety. Several of these compounds triggered severe ER swelling associated with strong proteasomal inhibition and consequently cell death, a feature that was not observed with respect to mode of action of the natural product. Significantly, an analysis from the National Cancer Institute sixty cell line testing did not reveal any correlations between the most potent derivative and any other compound in the database, except at high concentrations (LC 50 ). This study led to the discovery of a new set of sphaeropsidin derivatives that may be exploited as potential anti-cancer agents, notably due to their maintained activity towards multidrug resistant models., (© 2024. The Author(s).)

Ruthenium(ii) complexes are attracting significant research attention as a promising class of photosensitizers (PSs) in photodynamic therapy (PDT). Having previously reported the synthesis of two novel Ru(ii)-polypyridyl-1,8-naphthalimide Tröger's base compounds 1 and 2 with interesting photophysical properties, where the emission from either the Ru(ii) polypyridyl centres or the naphthalimide moieties could be used to monitor binding to nucleic acids, we sought to use these compounds to investigate further and in more detail their biological profiling, which included unravelling their mechanism of cellular uptake, cellular trafficking and cellular responses to photoexcitation. Here we demonstrate that these compounds undergo rapid time dependent uptake in HeLa cells that involved energy dependent, caveolae and lipid raft-dependent mediated endocytosis, as demonstrated by confocal imaging, and transmission and scanning electron microscopy. Following endocytosis, both compounds were shown to localise to mostly lysosomal and Golgi apparatus compartments with some accumulation in mitochondria but no localisation was found to the nucleus. Upon photoactivation, the compounds increased ROS production and induced ROS-dependent apoptotic cell death. The photo-activated compounds subsequently induced DNA damage and altered tubulin, but not actin structures, which was likely to be an indirect effect of ROS production and induced apoptosis. Furthermore, by changing the concentration of the compounds or the laser used to illuminate the cells, the mechanism of cell death could be changed from apoptosis to necrosis. This is the first detailed biological study of Ru(ii)-polypyridyl Tröger's bases and clearly suggests caveolae-dependent endocytosis is responsible for cell uptake - this may also explain the lack of nuclear uptake for these compounds and similar results observed for other Ru(ii)-polypyridyl complexes. These conjugates are potential candidates for further development as PDT agents and may also be useful in mechanistic studies on cell uptake and trafficking., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Apolipoproteins L1 and L3 (APOLs) are associated at the Golgi with the membrane fission factors phosphatidylinositol 4-kinase-IIIB (PI4KB) and non-muscular myosin 2A. Either APOL1 C-terminal truncation (APOL1Δ) or APOL3 deletion (APOL3-KO [knockout]) reduces PI4KB activity and triggers actomyosin reorganization. We report that APOL3, but not APOL1, controls PI4KB activity through interaction with PI4KB and neuronal calcium sensor-1 or calneuron-1. Both APOLs are present in Golgi-derived autophagy-related protein 9A vesicles, which are involved in PI4KB trafficking. Like APOL3-KO, APOL1Δ induces PI4KB dissociation from APOL3, linked to reduction of mitophagy flux and production of mitochondrial reactive oxygen species. APOL1 and APOL3, respectively, can interact with the mitophagy receptor prohibitin-2 and the mitophagosome membrane fusion factor vesicle-associated membrane protein-8 (VAMP8). While APOL1 conditions PI4KB and APOL3 involvement in mitochondrion fission and mitophagy, APOL3-VAMP8 interaction promotes fusion between mitophagosomal and endolysosomal membranes. We propose that APOL3 controls mitochondrial membrane dynamics through interactions with the fission factor PI4KB and the fusion factor VAMP8., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2023 The Author(s). Published by Elsevier Inc. All rights reserved.)

Medical implants have improved the quality of life of many patients. However, surgical intervention may eventually lead to implant microbial contamination. The aims of this research were to develop an easy, robust, quantitative assay to assess surface antimicrobial activities, especially the anti-nascent biofilm activity, and to identify control surfaces, allowing for international comparisons. Using new antimicrobial assays to assess the inhibition of nascent biofilm during persistent contact or after transient contact with bacteria, we show that the 5 cent Euro coin or other metal-based antibacterial coins can be used as positive controls, as more than 4 log reduction on bacterial survival was observed when using either S. aureus or P. aeruginosa as targets. The methods and controls described here could be useful to develop an easy, flexible and standardizable assay to assess relevant antimicrobial activities of new implant materials developed by industries and academics.

Approximately 20% of sleeping sickness patients exhibit respiratory complications, however, with a largely unknown role of the parasite. Here we show that tsetse fly-transmitted Trypanosoma brucei parasites rapidly and permanently colonize the lungs and occupy the extravascular spaces surrounding the blood vessels of the alveoli and bronchi. They are present as nests of multiplying parasites exhibiting close interactions with collagen and active secretion of extracellular vesicles. The local immune response shows a substantial increase of monocytes, macrophages, dendritic cells and γδ and activated αβ T cells and a later influx of neutrophils. Interestingly, parasite presence results in a significant reduction of B cells, eosinophils and natural killer cells. T. brucei infected mice show no infection-associated pulmonary dysfunction, mirroring the limited pulmonary clinical complications during sleeping sickness. However, the substantial reduction of the various immune cells may render individuals more susceptible to opportunistic infections, as evident by a co-infection experiment with respiratory syncytial virus. Collectively, these observations provide insights into a largely overlooked target organ, and may trigger new diagnostic and supportive therapeutic approaches for sleeping sickness., (© 2022. The Author(s).)

Brucellae are facultative intracellular Gram-negative coccobacilli that chronically infect various mammals and cause brucellosis. Human brucellosis is among the most common bacterial zoonoses and the vast majority of cases are attributed to B. melitensis. Using transposon sequencing (Tn-seq) analysis, we showed that among 3369 predicted genes of the B. melitensis genome, 861 are required for optimal growth in rich medium and 186 additional genes appeared necessary for survival of B. melitensis in RAW 264.7 macrophages in vitro. As the mucosal immune system represents the first defense against Brucella infection, we investigated the early phase of pulmonary infection in mice. In situ analysis at the single cell level indicates a succession of killing and growth phases, followed by heterogenous proliferation of B. melitensis in alveolar macrophages during the first 48 hours of infection. Tn-seq analysis identified 94 additional genes that are required for survival in the lung at 48 hours post infection. Among them, 42 genes are common to RAW 264.7 macrophages and the lung conditions, including the T4SS and purine synthesis genes. But 52 genes are not identified in RAW 264.7 macrophages, including genes implicated in lipopolysaccharide (LPS) biosynthesis, methionine transport, tryptophan synthesis as well as fatty acid and carbohydrate metabolism. Interestingly, genes implicated in LPS synthesis and β oxidation of fatty acids are no longer required in Interleukin (IL)-17RA-/- mice and asthmatic mice, respectively. This demonstrates that the immune status determines which genes are required for optimal survival and growth of B. melitensis in vivo., Competing Interests: The authors have declared that no competing interests exist.

The mitochondrion is crucial for ATP generation by oxidative phosphorylation, among other processes. Cristae are invaginations of the mitochondrial inner membrane that house nearly all the macromolecular complexes that perform oxidative phosphorylation. The unicellular parasite Trypanosoma brucei undergoes during its life cycle extensive remodeling of its single mitochondrion, which reflects major changes in its energy metabolism. While the bloodstream form (BSF) generates ATP exclusively by substrate-level phosphorylation and has a morphologically highly reduced mitochondrion, the insect-dwelling procyclic form (PCF) performs oxidative phosphorylation and has an expanded and reticulated organelle. Here, we have performed high-resolution 3D reconstruction of BSF and PCF mitochondria, with a particular focus on their cristae. By measuring the volumes and surface areas of these structures in complete or nearly complete cells, we have found that mitochondrial cristae are more prominent in BSF than previously thought and their biogenesis seems to be maintained during the cell cycle. Furthermore, PCF cristae exhibit a surprising range of volumes in situ, implying that each crista is acting as an independent bioenergetic unit. Cristae appear to be particularly enriched in the region of the organelle between the nucleus and kinetoplast, the mitochondrial genome, suggesting this part has distinctive properties., (© 2021 International Society of Protistologists.)

FAT1, which encodes a protocadherin, is one of the most frequently mutated genes in human cancers 1-5 . However, the role and the molecular mechanisms by which FAT1 mutations control tumour initiation and progression are poorly understood. Here, using mouse models of skin squamous cell carcinoma and lung tumours, we found that deletion of Fat1 accelerates tumour initiation and malignant progression and promotes a hybrid epithelial-to-mesenchymal transition (EMT) phenotype. We also found this hybrid EMT state in FAT1-mutated human squamous cell carcinomas. Skin squamous cell carcinomas in which Fat1 was deleted presented increased tumour stemness and spontaneous metastasis. We performed transcriptional and chromatin profiling combined with proteomic analyses and mechanistic studies, which revealed that loss of function of FAT1 activates a CAMK2-CD44-SRC axis that promotes YAP1 nuclear translocation and ZEB1 expression that stimulates the mesenchymal state. This loss of function also inactivates EZH2, promoting SOX2 expression, which sustains the epithelial state. Our comprehensive analysis identified drug resistance and vulnerabilities in FAT1-deficient tumours, which have important implications for cancer therapy. Our studies reveal that, in mouse and human squamous cell carcinoma, loss of function of FAT1 promotes tumour initiation, progression, invasiveness, stemness and metastasis through the induction of a hybrid EMT state.

Human innate immunity to Trypanosoma brucei involves the trypanosome C-terminal kinesin Tb KIFC1, which transports internalized trypanolytic factor apolipoprotein L1 (APOL1) within the parasite. We show that Tb KIFC1 preferentially associates with cholesterol-containing membranes and is indispensable for mammalian infectivity. Knockdown of Tb KIFC1 did not affect trypanosome growth in vitro but rendered the parasites unable to infect mice unless antibody synthesis was compromised. Surface clearance of Variant Surface Glycoprotein (VSG)-antibody complexes was far slower in these cells, which were more susceptible to capture by macrophages. This phenotype was not due to defects in VSG expression or trafficking but to decreased VSG mobility in a less fluid, stiffer surface membrane. This change can be attributed to increased cholesterol level in the surface membrane in Tb KIFC1 knockdown cells. Clearance of surface-bound antibodies by T. brucei is therefore essential for infectivity and depends on high membrane fluidity maintained by the cholesterol-trafficking activity of Tb KIFC1., Competing Interests: The authors declare that they have no competing financial interest., (© 2020 The Author(s).)

A unique feature of the African trypanosome Trypanosoma brucei is the presence of an outer layer made of densely packed variable surface glycoproteins (VSGs), which enables the cells to survive in the bloodstream. Although the VSG coat is critical to pathogenesis, how exactly the glycoproteins are organized at the nanoscale is poorly understood. Here, we show that multiparametric atomic force microscopy is a powerful nanoimaging tool for the structural and mechanical characterization of trypanosomes, in a label-free manner and in buffer solution. Directly correlated images of the structure and elasticity of trypanosomes enable us to identify multiple nanoscale mechanical heterogeneities on the cell surface. On a ∼250 nm scale, regions of softer (Young's modulus ∼50 kPa) and stiffer (∼100 kPa) elasticity alternate, revealing variations of the VSG coat and underlying structures. Our nanoimaging experiments show that the T. brucei cell surface is more heterogeneous than previously anticipated and offer promising prospects for the design of trypanocidal drugs targeting cell surface components., Competing Interests: The authors declare no competing financial interest., (Copyright © 2020 American Chemical Society.)

The C-terminal variants G1 and G2 of apolipoprotein L1 (APOL1) confer human resistance to the sleeping sickness parasite Trypanosoma rhodesiense, but they also increase the risk of kidney disease. APOL1 and APOL3 are death-promoting proteins that are partially associated with the endoplasmic reticulum and Golgi membranes. We report that in podocytes, either APOL1 C-terminal helix truncation (APOL1Δ) or APOL3 deletion (APOL3KO) induces similar actomyosin reorganization linked to the inhibition of phosphatidylinositol-4-phosphate [PI(4)P] synthesis by the Golgi PI(4)-kinase IIIB (PI4KB). Both APOL1 and APOL3 can form K + channels, but only APOL3 exhibits Ca 2+ -dependent binding of high affinity to neuronal calcium sensor-1 (NCS-1), promoting NCS-1-PI4KB interaction and stimulating PI4KB activity. Alteration of the APOL1 C-terminal helix triggers APOL1 unfolding and increased binding to APOL3, affecting APOL3-NCS-1 interaction. Since the podocytes of G1 and G2 patients exhibit an APOL1Δ or APOL3KO-like phenotype, APOL1 C-terminal variants may induce kidney disease by preventing APOL3 from activating PI4KB, with consecutive actomyosin reorganization of podocytes., Competing Interests: Declaration of Interests The authors declare no competing interests., (Copyright © 2020 The Author(s). Published by Elsevier Inc. All rights reserved.)

The primate-specific serum protein apolipoprotein L1 (APOL1) is the only secreted member of a family of cell death promoting proteins 1-4 . APOL1 kills the bloodstream parasite Trypanosoma brucei brucei, but not the human sleeping sickness agents T.b. rhodesiense and T.b. gambiense 3 . We considered the possibility that intracellular members of the APOL1 family, against which extracellular trypanosomes could not have evolved resistance, could kill pathogenic T. brucei subspecies. Here we show that recombinant APOL3 (rAPOL3) kills all African trypanosomes, including T.b. rhodesiense, T.b. gambiense and the animal pathogens Trypanosoma evansi, Trypanosoma congolense and Trypanosoma vivax. However, rAPOL3 did not kill more distant trypanosomes such as Trypanosoma theileri or Trypanosoma cruzi. This trypanolytic potential was partially shared by rAPOL1 from Papio papio (rPpAPOL1). The differential killing ability of rAPOL3 and rAPOL1 was associated with a distinct dependence on acidic pH for activity. Due both to its instability and toxicity when injected into mice, rAPOL3 cannot be used for the treatment of infection, but an experimental rPpAPOL1 mutant inspired by APOL3 exhibited enhanced trypanolytic activity in vitro and the ability to completely inhibit T.b. gambiense infection in mice. We conclude that pH dependence influences the trypanolytic potential of rAPOLs.

The microvillus brush border on the renal proximal tubule epithelium allows the controlled reabsorption of solutes that are filtered through the glomerulus and thus participates in general body homeostasis. Here, using the lipid 5-phosphatase Ship2 global knockout mice, proximal tubule-specific Ship2 knockout mice, and a proximal tubule cell model in which SHIP2 is inactivated, we show that SHIP2 is a negative regulator of microvilli formation, thereby controlling solute reabsorption by the proximal tubule. We found increased PtdIns(4,5)P2 substrate and decreased PtdIns4P product when SHIP2 was inactivated, associated with hyperactivated ezrin/radixin/moesin proteins and increased Rho-GTP. Thus, inactivation of SHIP2 leads to increased microvilli formation and solute reabsorption by the renal proximal tubule. This may represent an innovative therapeutic target for renal Fanconi syndrome characterized by decreased reabsorption of solutes by this nephron segment., (Copyright © 2017 International Society of Nephrology. Published by Elsevier Inc. All rights reserved.)

Cell division is a vital part of the cell cycle that is fundamental to all life. Despite decades of intense investigation, this process is still incompletely understood. Previously, the essential GTPase ObgE, which plays a role in a myriad of basic cellular processes (such as initiation of DNA replication, chromosome segregation, and ribosome assembly), was proposed to act as a cell cycle checkpoint in Escherichia coli by licensing chromosome segregation. We here describe the effect of a mutant isoform of ObgE (ObgE ∗ ) that causes cell death by irreversible arrest of the cell cycle at the stage of cell division. Notably, chromosome segregation is allowed to proceed normally in the presence of ObgE ∗ , after which cell division is blocked. Under conditions of rapid growth, ongoing cell cycles are completed before cell cycle arrest by ObgE ∗ becomes effective. However, cell division defects caused by ObgE ∗ then elicit lysis through formation of membrane blebs at aberrant division sites. Based on our results, and because ObgE was previously implicated in cell cycle regulation, we hypothesize that the mutation in ObgE ∗ disrupts the normal role of ObgE in cell division. We discuss how ObgE ∗ could reveal more about the intricate role of wild-type ObgE in division and cell cycle control. Moreover, since Obg is widely conserved and essential for viability, also in eukaryotes, our findings might be applicable to other organisms as well.

Apolipoproteins L (ApoLs) are Bcl-2-like proteins expressed under inflammatory conditions in myeloid and endothelial cells. We found that Toll-like receptor (TLR) stimuli, particularly the viral mimetic polyinosinic:polycytidylic acid (poly(I:C)), specifically induce ApoLs7/11 subfamilies in murine CD8α(+)  dendritic cells (DCs). This induction requires the TLR3/TRIF (where TRIF is TIR domain containing adapter-inducing interferon β) signaling pathway and is dependent on IFN-β in all ApoLs subfamilies except for ApoL7c. Poly(I:C) treatment of DCs is also associated with induction of both cell death and autophagy. ApoLs expression is related to promotion of DC death by poly(I:C), as ApoLs7/11 knockdown increases DC survival and ApoLs7 are associated with the anti-apoptotic protein Bcl-xL (where Bcl-xL is B-cell lymphoma extra large). Similarly, in human monocyte-derived DCs poly(I:C) induces both cell death and the expression of ApoLs, principally ApoL3. Finally, the BH3-like peptide of ApoLs appears to be involved in the DC death-promoting activity. We would like to propose that ApoLs are involved in cell death linked to activation of DCs by viral stimuli., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Tsetse flies are the sole vectors of Trypanosoma brucei parasites that cause sleeping sickness. Our knowledge on the early interface between the infective metacyclic forms and the mammalian host skin is currently highly limited. Glossina morsitans flies infected with fluorescently tagged T. brucei parasites were used in this study to initiate natural infections in mice. Metacyclic trypanosomes were found to be highly infectious through the intradermal route in sharp contrast with blood stream form trypanosomes. Parasite emigration from the dermal inoculation site resulted in detectable parasite levels in the draining lymph nodes within 18 hours and in the peripheral blood within 42 h. A subset of parasites remained and actively proliferated in the dermis. By initiating mixed infections with differentially labeled parasites, dermal parasites were unequivocally shown to arise from the initial inoculum and not from a re-invasion from the blood circulation. Scanning electron microscopy demonstrated intricate interactions of these skin-residing parasites with adipocytes in the connective tissue, entanglement by reticular fibers of the periadipocytic baskets and embedment between collagen bundles. Experimental transmission experiments combined with molecular parasite detection in blood fed flies provided evidence that dermal trypanosomes can be acquired from the inoculation site immediately after the initial transmission. High resolution thermographic imaging also revealed that intradermal parasite expansion induces elevated skin surface temperatures. Collectively, the dermis represents a delivery site of the highly infective metacyclic trypanosomes from which the host is systemically colonized and where a proliferative subpopulation remains that is physically constrained by intricate interactions with adipocytes and collagen fibrous structures.

Plant root-knot nematode (RKN) interaction studies are performed on several host plant models. Though RKN interact with trees, no perennial woody model has been explored so far. Here, we show that poplar (Populus tremula × P. alba) grown in vitro is susceptible to Meloidogyne incognita, allowing this nematode to penetrate, to induce feeding sites, and to successfully complete its life cycle. Quantitative reverse transcription-polymerase chain reaction analysis was performed to study changes in poplar gene expression in galls compared with noninfected roots. Three genes (expansin A, histone 3.1, and asparagine synthase), selected as gall development marker genes, followed, during poplar-nematode interaction, a similar expression pattern to what was described for other plant hosts. Downregulation of four genes implicated in the monolignol biosynthesis pathway was evidenced in galls, suggesting a shift in the phenolic profile within galls developed on poplar roots. Raman microspectroscopy demonstrated that cell walls of giant cells were not lignified but mainly composed of pectin and cellulose. The data presented here suggest that RKN exercise conserved strategies to reproduce and to invade perennial plant species and that poplar is a suitable model host to study specific traits of tree-nematode interactions.

Unlabelled: Programmed cell death (PCD) is an important hallmark of multicellular organisms. Cells self-destruct through a regulated series of events for the benefit of the organism as a whole. The existence of PCD in bacteria has long been controversial due to the widely held belief that only multicellular organisms would profit from this kind of altruistic behavior at the cellular level. However, over the past decade, compelling experimental evidence has established the existence of such pathways in bacteria. Here, we report that expression of a mutant isoform of the essential GTPase ObgE causes rapid loss of viability in Escherichia coli. The physiological changes that occur upon expression of this mutant protein--including loss of membrane potential, chromosome condensation and fragmentation, exposure of phosphatidylserine on the cell surface, and membrane blebbing--point to a PCD mechanism. Importantly, key regulators and executioners of known bacterial PCD pathways were shown not to influence this cell death program. Collectively, our results suggest that the cell death pathway described in this work constitutes a new mode of bacterial PCD., Importance: Programmed cell death (PCD) is a well-known phenomenon in higher eukaryotes. In these organisms, PCD is essential for embryonic development--for example, the disappearance of the interdigital web--and also functions in tissue homeostasis and elimination of pathogen-invaded cells. The existence of PCD mechanisms in unicellular organisms like bacteria, on the other hand, has only recently begun to be recognized. We here demonstrate the existence of a bacterial PCD pathway that induces characteristics that are strikingly reminiscent of eukaryotic apoptosis, such as fragmentation of DNA, exposure of phosphatidylserine on the cell surface, and membrane blebbing. Our results can provide more insight into the mechanism and evolution of PCD pathways in higher eukaryotes. More importantly, especially in the light of the looming antibiotic crisis, they may point to a bacterial Achilles' heel and can inspire innovative ways of combating bacterial infections, directed at the targeted activation of PCD pathways., (Copyright © 2015 Dewachter et al.)

Humans resist infection by the African parasite Trypanosoma brucei owing to the trypanolytic activity of the serum apolipoprotein L1 (APOL1). Following uptake by endocytosis in the parasite, APOL1 forms pores in endolysosomal membranes and triggers lysosome swelling. Here we show that APOL1 induces both lysosomal and mitochondrial membrane permeabilization (LMP and MMP). Trypanolysis coincides with MMP and consecutive release of the mitochondrial TbEndoG endonuclease to the nucleus. APOL1 is associated with the kinesin TbKIFC1, of which both the motor and vesicular trafficking VHS domains are required for MMP, but not for LMP. The presence of APOL1 in the mitochondrion is accompanied by mitochondrial membrane fenestration, which can be mimicked by knockdown of a mitochondrial mitofusin-like protein (TbMFNL). The BH3-like peptide of APOL1 is required for LMP, MMP and trypanolysis. Thus, trypanolysis by APOL1 is linked to apoptosis-like MMP occurring together with TbKIFC1-mediated transport of APOL1 from endolysosomal membranes to the mitochondrion.

Normal human serum (NHS) confers human resistance to infection by the parasite Trypanosoma brucei owing to the trypanolytic activity of apolipoprotein L1 (APOL1), present in two serum complexes termed Trypanolytic Factors (TLF-1 and -2). In order to identify parasite components involved in the intracellular trafficking and activity of TLFs, an inducible RNA interference (RNAi) genomic DNA library constructed in bloodstream form T. brucei was subjected to RNAi induction and selection for resistant parasites under NHS conditions favouring either TLF-1 or TLF-2 uptake. While TLF-1 conditions readily selected the haptoglobin-haemoglobin (HP-HB) surface receptor TbHpHbR as expected, given its known ability to bind TLF-1, under TLF-2 conditions no specific receptor for TLF-2 was identified. Instead, the screen allowed the identification of five distinct factors expected to be involved in the assembly of the vacuolar proton pump V-ATPase and consecutive endosomal acidification. These data confirm that lowering the pH during endocytosis is required for APOL1 toxic activity., (© 2014 John Wiley & Sons Ltd.)

Brucella spp. are facultative intracellular Gram-negative coccobacilli responsible for brucellosis, a worldwide zoonosis. We observed that Brucella melitensis is able to persist for several weeks in the blood of intraperitoneally infected mice and that transferred blood at any time point tested is able to induce infection in naive recipient mice. Bacterial persistence in the blood is dramatically impaired by specific antibodies induced following Brucella vaccination. In contrast to Bartonella, the type IV secretion system and flagellar expression are not critically required for the persistence of Brucella in blood. ImageStream analysis of blood cells showed that following a brief extracellular phase, Brucella is associated mainly with the erythrocytes. Examination by confocal microscopy and transmission electron microscopy formally demonstrated that B. melitensis is able to invade erythrocytes in vivo. The bacteria do not seem to multiply in erythrocytes and are found free in the cytoplasm. Our results open up new areas for investigation and should serve in the development of novel strategies for the treatment or prophylaxis of brucellosis. Invasion of erythrocytes could potentially protect the bacterial cells from the host's immune response and hamper antibiotic treatment and suggests possible Brucella transmission by bloodsucking insects in nature., (Copyright © 2014, American Society for Microbiology. All Rights Reserved.)

Humans can survive bloodstream infection by African trypanosomes, owing to the activity of serum complexes that have efficient trypanosome-killing ability. The two trypanosome subspecies that are responsible for human sleeping sickness--Trypanosoma brucei rhodesiense and Trypanosoma brucei gambiense--can evade this defence mechanism by expressing distinct resistance proteins. In turn, sequence variation in the gene that encodes the trypanosome-killing component in human serum has enabled populations in western Africa to restore resistance to T. b. rhodesiense, at the expense of the high probability of developing kidney sclerosis. These findings highlight the importance of resistance to trypanosomes in human evolution.

Immortal spheroids were generated from fetal mouse intestine using the culture system initially developed to culture organoids from adult intestinal epithelium. Spheroid proportion progressively decreases from fetal to postnatal period, with a corresponding increase in production of organoids. Like organoids, spheroids show Wnt-dependent indefinite self-renewing properties but display a poorly differentiated phenotype reminiscent of incompletely caudalized progenitors. The spheroid transcriptome is strikingly different from that of adult intestinal stem cells, with minimal overlap of Wnt target gene expression. The receptor LGR4, but not LGR5, is essential for their growth. Trop2/Tacstd2 and Cnx43/Gja1, two markers highly enriched in spheroids, are expressed throughout the embryonic-day-14 intestinal epithelium. Comparison of in utero and neonatal lineage tracing using Cnx43-CreER and Lgr5-CreERT2 mice identified spheroid-generating cells as developmental progenitors involved in generation of the prenatal intestinal epithelium. Ex vivo, spheroid cells have the potential to differentiate into organoids, qualifying as a fetal type of intestinal stem cell., (Copyright © 2013 The Authors. Published by Elsevier Inc. All rights reserved.)

The African parasite Trypanosoma brucei gambiense accounts for 97% of human sleeping sickness cases. T. b. gambiense resists the specific human innate immunity acting against several other tsetse-fly-transmitted trypanosome species such as T. b. brucei, the causative agent of nagana disease in cattle. Human immunity to some African trypanosomes is due to two serum complexes designated trypanolytic factors (TLF-1 and -2), which both contain haptoglobin-related protein (HPR) and apolipoprotein LI (APOL1). Whereas HPR association with haemoglobin (Hb) allows TLF-1 binding and uptake via the trypanosome receptor TbHpHbR (ref. 5), TLF-2 enters trypanosomes independently of TbHpHbR (refs 4, 5). APOL1 kills trypanosomes after insertion into endosomal/lysosomal membranes. Here we report that T. b. gambiense resists TLFs via a hydrophobic β-sheet of the T. b. gambiense-specific glycoprotein (TgsGP), which prevents APOL1 toxicity and induces stiffening of membranes upon interaction with lipids. Two additional features contribute to resistance to TLFs: reduction of sensitivity to APOL1 requiring cysteine protease activity, and TbHpHbR inactivation due to a L210S substitution. According to such a multifactorial defence mechanism, transgenic expression of T. b. brucei TbHpHbR in T. b. gambiense did not cause parasite lysis in normal human serum. However, these transgenic parasites were killed in hypohaptoglobinaemic serum, after high TLF-1 uptake in the absence of haptoglobin (Hp) that competes for Hb and receptor binding. TbHpHbR inactivation preventing high APOL1 loading in hypohaptoglobinaemic serum may have evolved because of the overlapping endemic area of T. b. gambiense infection and malaria, the main cause of haemolysis-induced hypohaptoglobinaemia in western and central Africa.

The MIR396 family, composed of ath-miR396a and ath-miR396b in Arabidopsis, is conserved among plant species and is known to target the Growth-Regulating Factor (GRF) gene family. ath-miR396 overexpressors or grf mutants are characterised by small and narrow leaves and show embryogenic defects such as cotyledon fusion. Heterologous expression of ath-miR396a has been reported in tobacco and resulted in reduction of the expression of three NtGRF genes. In this study, the precursor of the Populus trichocarpa ptc-miR396c, with a mature sequence identical to ath-miR396b, was expressed under control of the CaMV35S promoter in tobacco. Typical phenotypes of GRF down-regulation were observed, including cotyledon fusion and lack of shoot apical meristem (SAM). At later stage of growth, transgenic plants had delayed development and altered specification of organ type during flower development. The third and fourth whorls of floral organs were modified into stigmatoid anthers and fasciated carpels, respectively. Several NtGRF genes containing a miR396 binding site were found to be down-regulated, and the cleavage of their corresponding mRNA at the miR396 binding site was confirmed for two of them using RACE-PCR analysis. The data obtained agree with the functional conservation of the miR396 family in plants and suggest a role for the miR396/GRF network in determination of floral organ specification., (© 2012 German Botanical Society and The Royal Botanical Society of the Netherlands.)

FKBP12 proteins are able to inhibit TOR kinases or calcineurin phosphatases upon binding of rapamycin or FK506 drugs, respectively. The Trypanosoma brucei FKBP12 homologue (TbFKBP12) was found to be a cytoskeleton-associated protein with specific localization in the flagellar pocket area of the bloodstream form. In the insect procyclic form, RNA interference-mediated knockdown of TbFKBP12 affected motility. In bloodstream cells, depletion of TbFKBP12 affected cytokinesis and cytoskeleton architecture. These last effects were associated with the presence of internal translucent cavities limited by an inside-out configuration of the normal cell surface, with a luminal variant surface glycoprotein coat lined up by microtubules. These cavities, which recreated the streamlined shape of the normal trypanosome cytoskeleton, might represent unsuccessful attempts for cell abscission. We propose that TbFKBP12 differentially affects stage-specific processes through association with the cytoskeleton.

The multifunctionality of plant annexins and their importance for coordinating development and responses to biotic and abiotic environment have been largely reviewed. We recently described a tobacco annexin, named Ntann12, which is mainly localized in the nucleus of root cells when the plant is grown under light conditions. We also found that auxin and polar auxin transport are essential for Ntann12 accumulation in root cells. Under dark condition, Ntann12 is no longer detected in the root system. In the present addendum, light, regulating auxin signaling, is evidenced as an essential determinant for the synchronization of growth and development between the shoot and the root during light/dark cycle. A speculative model for Ntann12 is described and discussed with regards to relevant literature data.

Adjuvant efficiency is critical for inducing a protective and long-lasting immune response against weak immunogenic antigens. Discovered more than 70 years ago, aluminum salts remain the most widely used adjuvant in human vaccine. Prone to induce a strong humoral response, alum fails to drive a cell-mediated immunity, which is essential to fight against intracellular pathogens. Adjuvant systems that contain more than one component may represent an excellent alternative for completing the lack of T cell immunity associated with the injection of alum-based vaccine. In this work, we demonstrated that the adjuvant effects of alum strongly benefited from combining with a cationic lipid, the diC14 amidine. Indeed, we measured a significant improvement of alum-driven IL-1β release when human macrophages were co-cultured with a mixed suspension of alum and the diC14 amidine. Morphological analysis suggested that diC14 amidine improved the alum uptake by phagocytes. Furthermore, the addition of diC14 amidine to alum efficiently enhanced antigen processing and cross-presentation by antigen presenting cells. The biological relevance of these in vitro data was assessed by measuring the in vivo development of a cytotoxic activity and the enhanced synthesis of antigen-specific immunoglobulins after immunization with alum combined to diC14 amidine. Mechanistically, we demonstrated that diC14 amidine supported the alum adjuvanticity independently of the TLR-4 and caspase-1 agonist activities of the cationic lipid. Based on our findings, we conclude that diC14 amidine works synergistically with alum to achieve higher immune protection after vaccination., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

Ntann12, encoding a polypeptide homologous to annexins, was found previously to be induced upon infection of tobacco with the bacterium Rhodococcus fascians. In this study, Ntann12 is shown to bind negatively charged phospholipids in a Ca(2+)-dependent manner. In plants growing in light conditions, Ntann12 is principally expressed in roots and the corresponding protein was mainly immunolocalized in the nucleus. Ntann12 expression was inhibited following plant transfer to darkness and in plants lacking the aerial part. However, an auxin (indole-3-acetic acid) treatment restored the expression of Ntann12 in the root system in dark conditions. Conversely, polar auxin transport inhibitors such as 1-naphthylphthalamic acid (NPA) or 2,3,5-triiodobenzoic acid (TIBA) inhibited Ntann12 expression in light condition. These results indicate that the expression of Ntann12 in the root is linked to the perception of a signal in the aerial part of the plant that is transmitted to the root via polar auxin transport.

The African trypanosome Trypanosoma brucei, which persists within the bloodstream of the mammalian host, has evolved potent mechanisms for immune evasion. Specifically, antigenic variation of the variant-specific surface glycoprotein (VSG) and a highly active endocytosis and recycling of the surface coat efficiently delay killing mediated by anti-VSG antibodies. Consequently, conventional VSG-specific intact immunoglobulins are non-trypanocidal in the absence of complement. In sharp contrast, monovalent antigen-binding fragments, including 15 kDa nanobodies (Nb) derived from camelid heavy-chain antibodies (HCAbs) recognizing variant-specific VSG epitopes, efficiently lyse trypanosomes both in vitro and in vivo. This Nb-mediated lysis is preceded by very rapid immobilisation of the parasites, massive enlargement of the flagellar pocket and major blockade of endocytosis. This is accompanied by severe metabolic perturbations reflected by reduced intracellular ATP-levels and loss of mitochondrial membrane potential, culminating in cell death. Modification of anti-VSG Nbs through site-directed mutagenesis and by reconstitution into HCAbs, combined with unveiling of trypanolytic activity from intact immunoglobulins by papain proteolysis, demonstrates that the trypanolytic activity of Nbs and Fabs requires low molecular weight, monovalency and high affinity. We propose that the generation of low molecular weight VSG-specific trypanolytic nanobodies that impede endocytosis offers a new opportunity for developing novel trypanosomiasis therapeutics. In addition, these data suggest that the antigen-binding domain of an anti-microbial antibody harbours biological functionality that is latent in the intact immunoglobulin and is revealed only upon release of the antigen-binding fragment.

During the course of mammalian infection, African trypanosomes undergo extensive cellular differentiation, as actively dividing long slender (SL) forms progressively transform into intermediate (I) forms and finally quiescent G(1)/G(0)-locked short stumpy (ST) forms. ST forms maintain adaptations compatible with their survival in the mammalian bloodstream, such as high endocytic activity, but they already show preadaptations to the insect midgut conditions. The nutritional requirements of ST forms must differ from those of SL forms because the ST forms stop multiplying. We report that the uptake of several ligands was reduced in ST forms compared with that in SL forms. In particular, the haptoglobin-hemoglobin (Hp-Hb) complex was no longer taken up due to dramatic downregulation of its cognate receptor, TbHpHbR. As this receptor also allows uptake of trypanolytic particles from human serum, ST forms were resistant to trypanolysis by human serum lipoproteins. These observations allowed both flow cytometry analysis of SL-to-ST differentiation and the generation of homogeneous ST populations after positive selection upon exposure to trypanolytic particles. In addition, we observed that in ST forms the lysosome relocates anterior to the nucleus. Altogether, we identified novel morphological and molecular features that characterize SL-to-ST differentiation.

The primary cilium is an antenna-like structure that protrudes from the cell surface of quiescent/differentiated cells and participates in extracellular signal processing. Here, we report that mice deficient for the lipid 5-phosphatase Inpp5e develop a multiorgan disorder associated with structural defects of the primary cilium. In ciliated mouse embryonic fibroblasts, Inpp5e is concentrated in the axoneme of the primary cilium. Inpp5e inactivation did not impair ciliary assembly but altered the stability of pre-established cilia after serum addition. Blocking phosphoinositide 3-kinase (PI3K) activity or ciliary platelet-derived growth factor receptor alpha (PDGFRalpha) restored ciliary stability. In human INPP5E, we identified a mutation affecting INPP5E ciliary localization and cilium stability in a family with MORM syndrome, a condition related to Bardet-Biedl syndrome. Together, our results show that INPP5E plays an essential role in the primary cilium by controlling ciliary growth factor and PI3K signaling and stability, and highlight the consequences of INPP5E dysfunction.

Protozoan Kinetoplastida, a group that comprises the pathogenic Trypanosoma brucei, compartmentalize several metabolic systems such as the major part of the glycolytic pathway, in multiple peroxisome-like organelles, designated glycosomes. Trypanosomes have a complicated life cycle, involving two major, distinct stages living in the mammalian bloodstream and several stages inhabiting different body parts of the tsetse fly. Previous studies on non-differentiating trypanosomes have shown that the metabolism and enzymatic contents of glycosomes in bloodstream-form and cultured procyclic cells, representative of the stage living in the insect's midgut, differ considerably. In this study, the morphology of glycosomes and their position relative to the lysosome were followed, as were the levels of some glycosomal enzymes and markers for other subcellular compartments, during the differentiation from bloodstream-form to procyclic trypanosomes. Our studies revealed a small tendency of glycosomes to associate with the lysosome when a population of long-slender bloodstream forms differentiated into short-stumpy forms which are pre-adapted to live in the fly. The same phenomenon was observed during the short-stumpy to procyclic transformation, but then the process was fast and many more glycosomes were associated with the dramatically enlarged degradation organelle. The observations suggested an efficient glycosome turnover involving autophagy. Changes observed in the levels of marker enzymes are consistent with the notion that, during differentiation, glycosomes with enzymatic contents specific for the old life-cycle stage are degraded and new glycosomes with different contents are synthesized, causing that the metabolic repertoire of trypanosomes is, at each stage, optimally adapted to the environmental conditions encountered.

The contribution of the B isoform of inositol 1,4,5-trisphosphate [Ins(1,4,5)P(3)] 3-kinase (or Itpkb) and inositol 1,3,4,5-tetrakisphosphate [Ins(1,3,4,5)P(4)], its reaction product, to B cell function and development remains unknown. Here, we show that mice deficient in Itpkb have defects in B cell survival leading to specific and intrinsic developmental alterations in the B cell lineage and antigen unresponsiveness in vivo. The decreased B cell survival is associated with a decreased phosphorylation of Erk1/2 and increased Bim gene expression. B cell survival, development, and antigen responsiveness are normalized in parallel to reduced expression of Bim in Itpkb(-/-) Bim(+/-) mice. Analysis of the signaling pathway downstream of Itpkb revealed that Ins(1,3,4,5)P(4) regulates subcellular distribution of Rasa3, a Ras GTPase-activating protein acting as an Ins(1,3,4,5)P(4) receptor. Together, our results indicate that Itpkb and Ins(1,3,4,5)P(4) mediate a survival signal in B cells via a Rasa3-Erk signaling pathway controlling proapoptotic Bim gene expression.

We have previously identified TGSGP as a gene specific to the Trypanosoma brucei gambiense subspecies. TGSGP is a truncated VSG-like telomeric gene transcribed by RNA polymerase II. The TGSGP protein localizes to the flagellar pocket, and exhibits features compatible with a role as surface receptor. Here we show that TGSGP is physically linked to a truncation of a gene homologous to yeast AUT1 (APG3), a gene involved in internal vesicular formation. Further analysis indicated that T. b. gambiense is heterozygous for AUT1 (AUT1/aut1), with each allele located on independent chromosome II homologues. In 18 T. b. gambiense isolates from distinct geographical origins and different hosts, this genomic rearrangement was conserved. The size of the intergenic region between TGSGP and truncated aut1 varied among isolates but was similar in isolates of the same geographical area, and this observation may be used in epidemiology to trace the geographical origin of T. b. gambiense isolates.

African trypanosomes (the prototype of which is Trypanosoma brucei brucei) are protozoan parasites that infect a wide range of mammals. Human blood, unlike the blood of other mammals, has efficient trypanolytic activity, and this needs to be counteracted by these parasites. Resistance to this activity has arisen in two subspecies of Trypanosoma brucei - Trypanosoma brucei rhodesiense and Trypanosoma brucei gambiense - allowing these parasites to infect humans, and this results in sleeping sickness in East Africa and West Africa, respectively. Study of the mechanism by which T. b. rhodesiense escapes lysis by human serum led to the identification of an ionic-pore-forming apolipoprotein - known as apolipoprotein L1 - that is associated with high-density-lipoprotein particles in human blood. In this Opinion article, we argue that apolipoprotein L1 is the factor that is responsible for the trypanolytic activity of human serum.

Apolipoprotein L-I is the trypanolytic factor of human serum. Here we show that this protein contains a membrane pore-forming domain functionally similar to that of bacterial colicins, flanked by a membrane-addressing domain. In lipid bilayer membranes, apolipoprotein L-I formed anion channels. In Trypanosoma brucei, apolipoprotein L-I was targeted to the lysosomal membrane and triggered depolarization of this membrane, continuous influx of chloride, and subsequent osmotic swelling of the lysosome until the trypanosome lysed.

Antigenic variation allows African trypanosomes to develop chronic infections in mammalian hosts. This process results from the alternative occurrence of transcriptional switching and DNA recombination targeted to a telomeric locus that contains the gene of the variant antigen and is subjected to mono-allelic expression control. So far, the identification of mechanisms and factors involved still resists technological developments and genome sequencing.

Transcription of the variant surface glycoprotein (VSG) gene of Trypanosoma brucei occurs in a single of multiple polycistronic expression sites (ESs). Analysis of RNA from proliferative long slender (LS) bloodstream forms demonstrated that initiation of transcription occurs in different ESs, but inefficient RNA processing and elongation is linked to RNA polymerase arrest in all except one unit at a time. The pattern of ES transcripts was analysed during the transformation of dividing LS forms into quiescent short stumpy (SS) forms. The results demonstrated that the mono-allelic control allowing preferential RNA production from a given ES stops during this process. Accordingly, the steady-state ES transcripts, particularly the VSG mRNA, were strongly reduced. However, transcripts from the beginning of different ESs were still synthesized, and in vitro run-on transcription analysis indicated that RNA polymerase was still fully associated with the promoter-proximal half of the 'active' ES. Analysis of transcripts from two central tandem genes confirmed the existence of a residual decreasing transcriptional gradient in the 'active' ES of SS forms. Thus, in these forms the RNA polymerase of the ES is inactivated in situ. This inactivation is accompanied by a strong overall reduction of nuclear DNA transcription. Although cAMP is involved in the LS to SS transformation, no direct effect of cAMP was observed on the VSG ES control.

Actin is expressed at similar levels but in different locations in bloodstream and procyclic forms of Trypanosoma brucei. In bloodstream forms actin colocalizes with the highly polarized endocytic pathway, whereas in procyclic forms it is distributed throughout the cell. RNA interference demonstrated that in bloodstream forms, actin is an essential protein. Depletion of actin resulted in a rapid arrest of cell division, termination of vesicular traffic from the flagellar pocket membrane leading to gross enlargement of the pocket, loss of endocytic activity and eventually cell death. These results indicate that actin is required for the formation of coated vesicles from the flagellar pocket membrane, which is the first step in the endocytic pathway. Although loss of actin in procyclic cells did not affect growth, the trans region of the Golgi became distorted and enlarged and appeared to give rise to a heterogeneous population of vesicles. However, the flagellar pocket was not affected. These findings suggest that trypanosomes have different functional requirements for actin during the bloodstream and procyclic phases of the life cycle.

The variant surface glycoprotein (VSG) genes of Trypanosoma brucei are transcribed in telomeric loci termed VSG expression sites (ESs). Despite permanent initiation of transcription in most if not all of these multiple loci, RNA elongation is abortive except in bloodstream forms where full transcription up to the VSG occurs only in a single ES at a time. The ESs active in bloodstream forms are polycistronic and contain several genes in addition to the VSG, named ES-associated genes (ESAGs). So far 12 ESAGs have been identified, some of which are present only in some ESs. Most of these genes encode surface proteins and this list includes different glycosyl phosphatidyl inositol (GPI)-anchored proteins such as the heterodimeric receptor for the host transferrin (ESAG7/6), integral membrane proteins such as the receptor-like transmembrane adenylyl cyclase (ESAG4) and a surface transporter (ESAG10). An interesting exception is ESAG8, which may encode a cell cycle regulator involved in the differentiation of long slender into short stumpy bloodstream forms. Several ESAGs belong to multigene families including pseudogenes and members transcribed out of the ESs, named genes related to ESAGs (GRESAGs). However, some ESAGs (7, 6 and 8) appear to be restricted to the ESs. Most of these genes can be deleted from the active ES without apparently affecting the phenotype of bloodstream form trypanosomes, probably either due to the expression of ESAGs from 'inactive' ESs (ESAG7/6) or due to the expression of GRESAGs (in particular, GRESAGs4 and GRESAGs1). At least three ESAGs (ESAG7, ESAG6 and SRA) share the evolutionary origin of VSGs. The presence of these latter genes in ESs may confer an increased capacity of the parasite for adaptation to various mammalian hosts, as suggested in the case of ESAG7/6 and proven for SRA, which allows T. brucei to infect humans. Similarly, the existence of a collection of slightly different ESAG4s in the multiple ESs might provide the parasite with adenylyl cyclase isoforms that may regulate growth in response to different environmental conditions. The high transcription rate and high recombination level that prevail in VSG ESs may have favored the generation and/or recruitment in these sites of genes whose hyper-evolution allows adaptation to a larger variety of hosts.

The genome of Trypanosoma brucei contains about 120 chromosomes, which do not visibly condense during mitosis. We have analyzed the organization and segregation of these chromosomes by in situ hybridization using fluorescent telomere probes. At the onset of mitosis, telomeres migrate from their nuclear peripheral location and congregate into a central zone. This dense group of telomeres then splits into two entities that migrate to opposite nuclear poles. Segregation continues until the double-sized nucleus divides and, before cytokinesis occurs, the telomeres reorganize into the discrete foci observed at interphase. During migration, the telomeres are located at the free end of the mitotic spindle. Treatment with the microtubule polymerization inhibitor rhizoxin prevents telomere clustering and chromosomal segregation. In the insect-specific procyclic form as well as in the non-dividing bloodstream stumpy form, telomeres tend to cluster close to the nuclear periphery at interphase. In contrast, in the proliferative bloodstream slender form the telomeres preferentially locate in the central zone of the nucleus. Thus, telomeres are closer to the nuclear periphery during those life cycle stages where the telomeric expression sites for the variant surface glycoprotein are all inactive, suggesting that transcriptional inactivation of these sites is related to their subnuclear localization.

Trypanosoma brucei gambiense and T. b. rhodesiense are protozoan parasites causing sleeping sickness in humans due to their resistance to lysis by normal human serum (NHS). Based on the observation that the resistance gene of T. b. rhodesiense encodes a truncated form of the variant specific glycoprotein (VSG), we cloned a similar gene in T. b. gambiense using reverse transcription-linked polymerase chain reaction with VSG-specific primers. This gene, termed TgsGP for T. gambiense-specific glycoprotein, was found to be specific to T. b. gambiense. It is located close to a telomere and is transcribed by a pol II RNA polymerase, only at the bloodstream stage of the parasite development. TgsGP encodes a 47-kDa protein consisting of a N-terminal VSG domain presumably provided with a glycosylphosphatidylinositol (GPI) anchor sequence, similar to the pESAG6 subunit of the trypanosomal transferrin receptor. TgsGP is located in the flagellar pocket, and contains the linear N-linked polyacetyllactosamine characteristic of the endocytotic machinery of T. brucei. These observations strongly suggest that TgsGP is a T. b. gambiense specific receptor. Since stable expression of this protein in T. b. brucei did not confer resistance to NHS, TgsGP may either need another factor to achieve this purpose or fulfils another function linked to adaptation of the parasite to man.

The protozoan parasite Trypanosoma brucei relies on trans-splicing of a common spliced leader (SL) RNA to maturate mRNAs. Using the yeast two-hybrid system a protein (TSR1IP) was identified that interacts with the T. brucei serine-arginine (SR) protein termed TSR1. TSR1IP shows homology to U1 70 kDa proteins, and contains an SR rich domain as well as an acidic/arginine domain homologous to the U1 70 kDa poly(A) polymerase inhibiting domain. This protein is localized in the nucleoplasm and excluded from the nucleolus in trypanosomal bloodstream and procyclic forms. Based on structural modelling predictions and on the identification of a RNA recognition motif (RRM), it was possible to demonstrate by the yeast three-hybrid system that TSR1IP interacts with the 5' splice region of the SL RNA. All the above characteristics suggest that TSR1IP could be involved in trans-splicing.

The protozoan parasite Trypanosoma brucei relies on trans-splicing to process its mRNAs. A novel nuclear serine/arginine (SR)-rich trypanosomal protein (TSR1) was characterized which contains two RNA recognition motifs. The TSR1 protein appears to be homologous to RNA-binding SR proteins of the cis-splicing machinery from higher eukaryotes. Moreover, in the yeast two-hybrid system, TSR1 is able to interact with the human splicing factors involved in the recognition of the 3' splicing site (U2AF35/U2AF65). In both procyclic and bloodstream forms of T. brucei, TSR1 was found to localize in the nucleus. In the bloodstream stage TSR1 showed the speckles pattern characteristic of SR proteins involved in cis-splicing. Moreover, TSR1 was able to specifically bind the spliced leader (SL) RNA involved in trans-splicing in trypanosomes by the yeast three-hybrid system. These and other observations suggest that TSR1 may be involved in trans-splicing in T. brucei.

The use of the two-hybrid system in yeast allowed us to isolate a new mitochondrial protein of Trypanosoma brucei, termed PIE8, for putative protein interacting with ESAG8. This protein was found to localize progressively in the single mitochondrion of the parasite during the mitochondrial reactivation needed to adapt the parasite from the glycolysis-based metabolism in the mammalian host, to the cytochrome-mediated respiration in the fly vector. Once this reactivation is established, PIE8 is lost from the mitochondrion. Thus, the temporary presence of PIE8 in the mitochondrion is linked to mitochondrial reactivation.

Kinetoplast DNA, the mitochondrial DNA of trypanosomatid parasites, is a network containing several thousand minicircles and a few dozen maxicircles. We compared kinetoplast DNA replication in Trypanosoma brucei and Crithidia fasciculata using fluorescence in situ hybridization and electron microscopy of isolated networks. One difference is in the location of maxicircles in situ. In C. fasciculata, maxicircles are concentrated in discrete foci embedded in the kinetoplast disk; during replication the foci increase in number but remain scattered throughout the disk. In contrast, T. brucei maxicircles generally fill the entire disk. Unlike those in C. fasciculata, T. brucei maxicircles become highly concentrated in the central region of the kinetoplast after replication; then during segregation they redistribute throughout the daughter kinetoplasts. T. brucei and C. fasciculata also differ in the pattern of attachment of newly synthesized minicircles to the network. In C. fasciculata it was known that minicircles are attached at two antipodal sites but subsequently are found uniformly distributed around the network periphery, possibly due to a relative movement of the kinetoplast disk and two protein complexes responsible for minicircle synthesis and attachment. In T. brucei, minicircles appear to be attached at two antipodal sites but then remain concentrated in these two regions. Therefore, the relative movement of the kinetoplast and the two protein complexes may not occur in T. brucei.

Kinetoplast DNA (kDNA), the mitochondrial DNA of Crithidia fasciculata and related trypanosomatids, is a network containing approximately 5,000 covalently closed minicircles which are topologically interlocked. kDNA synthesis involves release of covalently closed minicircles from the network, and, after replication of the free minicircles, reattachment of the nicked or gapped progeny minicircles to the network periphery. We have investigated this process by electron microscopy of networks at different stages of replication. The distribution of nicked and closed minicircles is easily detectable either by autoradiography of networks radiolabeled at endogenous nicks by nick translation or by twisting the covalently closed minicircles with intercalating dye. The location of newly synthesized minicircles within the network is determined by autoradiography of network is determined by autoradiography of networks labeled in vivo with a pulse of [3H]thymidine. These studies have clarified structural changes in the network during replication, the timing of repair of nicked minicircles after replication, and the mechanism of division of the network.