66 research outputs found
The Plasmodium falciparum, Nima-related kinase Pfnek-4: a marker for asexual parasites committed to sexual differentiation
No full text<b>Background</b>
Malaria parasites undergo, in the vertebrate host, a developmental switch from asexual replication to sexual differentiation leading to the formation of gametocytes, the only form able to survive in the mosquito vector. Regulation of the onset of the sexual phase remains largely unknown and represents an important gap in the understanding of the parasite's complex biology.
<b>Methods:</b>
The expression and function of the Nima-related kinase Pfnek-4 during the early sexual development of the human malaria parasite Plasmodium falciparum were investigated, using three types of transgenic Plasmodium falciparum 3D7 lines: (i) episomally expressing a Pfnek-4-GFP fusion protein under the control of its cognate pfnek-4 promoter; (ii) episomally expressing negative or positive selectable markers, yeast cytosine deaminase-uridyl phosphoribosyl transferase, or human dihydrofolate reductase, under the control of the pfnek-4 promoter; and (iii) lacking a functional pfnek-4 gene. Parasite transfectants were analysed by fluorescence microscopy and flow cytometry. In vitro growth rate and gametocyte formation were determined by Giemsa-stained blood smears.
<b>Results:</b>
The Pfnek-4-GFP protein was found to be expressed in stage II to V gametocytes and, unexpectedly, in a subset of asexual-stage parasites undergoing schizogony. Culture conditions stimulating gametocyte formation resulted in significant increase of this schizont subpopulation. Moreover, sorted asexual parasites expressing the Pfnek-4-GFP protein displayed elevated gametocyte formation when returned to in vitro culture in presence of fresh red blood cells, when compared to GFP- parasites from the same initial population. Negative selection of asexual parasites expressing pfnek-4 showed a marginal reduction in growth rate, whereas positive selection caused a marked reduction in parasitaemia, but was not sufficient to completely abolish proliferation. Pfnek-4- clones are not affected in their asexual growth and produced normal numbers of stage V gametocytes.
<b>Conclusions:</b>
The results indicate that Pfnek-4 is not strictly gametocyte-specific, and is expressed in a small subset of asexual parasites displaying high rate conversion to sexual development. Pfnek-4 is not required for erythrocytic schizogony and gametocytogenesis. This is the first study to report the use of a molecular marker for the sorting of sexually-committed schizont stage P. falciparum parasites, which opens the way to molecular characterization of this pre-differentiated subpopulation
Etudes fonctionnelles de l'interleukine 1 et des facteurs promoteurs B
No full textSIGLECNRS T 55981 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc
Origine genetique et pathogenicite des auto-anticorps
No full textSIGLEINIST T 76354 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc
A NIMA-related protein kinase is essential for completion of the sexual cycle of malaria parasites
No full textThe molecular mechanisms regulating the sexual development of malaria parasites from gametocytes to oocysts in their mosquito vector are still largely unexplored. In other eukaryotes, NIMA-related kinases (Neks) regulate cell cycle progression and have been implicated in the regulation of meiosis. Here, we demonstrate that Nek-4, a new Plasmodium member of the Nek family, is essential for completion of the sexual cycle of the parasite. Recombinant Plasmodium falciparum Nek-4 possesses protein kinase activity and displays substrate preferences similar to those of other Neks. Nek-4 is highly expressed in gametocytes, yet disruption of the nek-4 gene in the rodent malaria parasite P. berghei has no effect on gamete formation and subsequent fertilization. However, further differentiation of zygotes into ookinetes is abolished. Measurements of nuclear DNA content indicate that zygotes lacking Nek-4 fail to undergo the genome replication to the tetraploid level that precedes meiosis. Cell cycle progression in the zygote is identified as a likely precondition for its morphological transition to the ookinete and for the successful establishment of a malaria infection in the mosquito.INSERM-EPF
MURINE AUTOANTIBODIES SPECIFIC FOR BROMELINIZED RED BLOOD CELLS USE A RESTRICTED SET OF GENETIC ELEMENTS AND THEIR HEAVY CHAINS DEFINE A NOVEL VH FAMILY
No full textAn essential role for the plasmodium nek-2 NIMA-related protein kinase in the sexual development of malaria parasites
No full textThe molecular control of cell division and development in malaria parasites is far from understood. We previously showed that a Plasmodium gametocyte-specific NIMA-related protein kinase, nek-4, is required for completion of meiosis in the ookinete, the motile form that develops from the zygote in the mosquito vector. Here, we show that another NIMA-related kinase, Pfnek-2, is also predominantly expressed in gametocytes, and that Pfnek-2 is an active enzyme displaying an in vitro substrate preference distinct from that of Pfnek-4. A functional nek-2 gene is required for transmission of both Plasmodium falciparum and the rodent malaria parasite Plasmodium berghei to the mosquito vector, which is explained by the observation that disruption of the nek-2 gene in P. berghei causes dysregulation of DNA replication during meiosis and blocks ookinete development. This has implications (i) in our understanding of sexual development of malaria parasites and (ii) in the context of control strategies aimed at interfering with malaria transmissio
SAM domain-dependent activity of PfTKL3, an essential tyrosine kinase-like kinase of the human malaria parasite Plasmodium falciparum
No full textOver the last decade, several protein kinases inhibitors have reached the market for cancer chemotherapy. The kinomes of pathogens represent potentially attractive targets in infectious diseases. The functions of the majority of protein kinases of Plasmodium falciparum, the parasitic protist responsible for the most virulent form of human malaria, remain unknown. Here we present a thorough characterisation of PfTKL3 (PF13_0258), an enzyme that belongs to the tyrosine kinase-like kinase (TKL) group. We demonstrate by reverse genetics that PfTKL3 is essential for asexual parasite proliferation in human erythrocytes. PfTKL3 is expressed in both asexual and gametocytes stages, and in the latter the protein co-localises with cytoskeleton microtubules. Recombinant PfTKL3 displays in vitro autophosphorylation activity and is able to phosphorylate exogenous substrates, and both activities are dramatically dependent on the presence of an N-terminal "sterile alpha-motif" domain. This study identifies PfTKL3 as a validated drug target amenable to high-throughput screening.INSERM-EPFLNational Licence
Autoantibody repertoire analysis in normal and lupus-prone mice
No full textWe have analyzed at the clonal level (limiting dilution assay) the repertoire of lipopolysaccharide (LPS)-responsive murine B cells committed to the production of autoantibodies characteristic of systemic lupus erythematous (SLE), i.e. anti-single-stranded DNA (ssDNA), anti-double-stranded DNA, anti-Sm and rheumatoid factors (RF). Our results demonstrated that: (1) the frequency of precursor B cells producing each lupus autoantibody (approximately 1 in every 100-400 LPS-responding B cell) was similar in two non-autoimmune (C57BL/6 and BALB/c) and four SLE-prone (NZB, (NZB x NZW)F1, MRL/MpJ and BXSB/MpJ) mice despite the marked differences in autoimmune responses in the different SLE-prone mice, and (2) the relative frequency of autoantibody-secreting precursor B cells was constant throughout life, and equally distributed among activated and resting B-cell populations and among B cells from the peritoneal cavity and spleen. The lack of association of anti-ssDNA secretion with anti-Sm or RF secretion in cultures set up with a smaller number of B cells ruled out the possibility that the similar frequency of different autoantibody-secreting cell precursors is due to the poly-specificity of IgM autoantibodies. Notably, the frequencies of autoantibody-secreting precursor cells were significantly lower, approximately 4 and 10 times, than those of anti-tetanus toxoid and anti-dinitrophenyl antibody-producing precursor B cells, respectively. The similar frequency of precursor B cells producing four different lupus autoantibodies on the one hand and the considerable variation in each autoimmune response among SLE-prone mice on the other, support the hypothesis that specific stimulatory mechanisms may govern each autoimmune response in different SLE strains of mice
Hisaki Hashi: Das Paradoxon in der Philosophie – Zum Aufbau der humanistischen Welt
No full textHashi Hisaki, the author of this interesting book, is founder of the Association for Comparative Philosophy and Interdisciplinary Education (http://kophil-interdis.at/wb/pages/home.php). Since 1995 she has taught at the Department of Philosophy at the University of Vienna, Austria. The present book is written in German, as it is based upon Hashi Hisaki’s philosophy lectures at this university. It elaborates upon intercultural dimensions of a wide scope of problems, linked to the concept of paradox, starting from the famous classical “liar paradox” and then analysing various paradoxes exemplified in the works of Plato, Kant, Hegel, Klein, Reininger, Nagarjuna, Hanfezi, Dogen, and Nishida. The main goal of the work is to illuminate the creative function of paradoxes, and to show that it can raise in readers a vivid interest in independent and critical thinking. At the same time, it represents an inexhaustible source of integrative thinking and acting in our daily life.Hashi Hisaki, the author of this interesting book, is founder of the Association for Comparative Philosophy and Interdisciplinary Education (http://kophil-interdis.at/wb/pages/home.php). Since 1995 she has taught at the Department of Philosophy at the University of Vienna, Austria. The present book is written in German, as it is based upon Hashi Hisaki’s philosophy lectures at this university. It elaborates upon intercultural dimensions of a wide scope of problems, linked to the concept of paradox, starting from the famous classical “liar paradox” and then analysing various paradoxes exemplified in the works of Plato, Kant, Hegel, Klein, Reininger, Nagarjuna, Hanfezi, Dogen, and Nishida. The main goal of the work is to illuminate the creative function of paradoxes, and to show that it can raise in readers a vivid interest in independent and critical thinking. At the same time, it represents an inexhaustible source of integrative thinking and acting in our daily life
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