The Experts below are selected from a list of 30432 Experts worldwide ranked by ideXlab platform
Boris Striepen - One of the best experts on this subject based on the ideXlab platform.
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a toxoplasma morn1 null mutant undergoes repeated divisions but is defective in basal assembly apicoplast division and cytokinesis
PLOS ONE, 2010Co-Authors: Alexander Lorestani, Boris Striepen, Lilach Sheiner, Kevin Yang, Seth D Robertson, Nivedita Sahoo, Carrie F Brooks, David J P Ferguson, Marc-jan GubbelsAbstract:The membrane occupation and recognition nexus protein 1 (MORN1) is highly conserved among apicomplexan parasites and is associated with several structures that have a role in Cell division. Here we dissected the role of MORN1 using the relatively simple Budding process of Toxoplasma gondii as a model. Ablation of MORN1 in a conditional null mutant resulted in pronounced defects suggesting a central role for MORN1 in apicoplast segregation and in daughter Cell Budding. Lack of MORN1 resulted in double-headed parasites. These Janus-headed parasites form two complete apical complexes but fail to assemble a basal complex. Moreover, these parasites were capable of undergoing several more Budding rounds resulting in the formation of up to 16-headed parasites conjoined at the basal end. Despite this segregation defect, the mother's cytoskeleton was completely disassembled in every Budding round. Overall this argues that successful completion of the Budding is not required for Cell cycle progression. None of the known basal complex components, including a set of recently identified inner membrane complex (IMC) proteins, localized correctly in these multi-headed parasites. These data suggest that MORN1 is essential for assembly of the basal complex, and that lack of the basal complex abolishes the contractile capacity assigned to the basal complex late in daughter formation. Consistent with this hypothesis we observe that MORN1 mutants fail to efficiently constrict and divide the apicoplast. We used the null background provided by the mutant to dissect the function of subdomains of the MORN1 protein. This demonstrated that deletion of a single MORN domain already prevented the function of MORN1 whereas a critical role for the short linker between MORN domains 6 and 7 was identified. In conclusion, MORN1 is required for basal complex assembly and loss of MORN1 results in defects in apicoplast division and daughter segregation.
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a morn repeat protein is a dynamic component of the toxoplasma gondii Cell division apparatus
Journal of Cell Science, 2006Co-Authors: Marc-jan Gubbels, Shipra Vaishnava, Nico Boot, Jean Francois Dubremetz, Boris StriepenAbstract:Apicomplexan parasites divide and replicate through a complex process of internal Budding. Daughter Cells are preformed within the mother on a cytoskeletal scaffold, endowed with a set of organelles whereby in the final stages the mother disintegrates and is recycled in the emerging daughters. How the cytoskeleton and the various endomembrane systems interact in this dynamic process remains poorly understood at the molecular level. Through a random YFP fusion screen we have identified two Toxoplasma gondii proteins carrying multiple membrane occupation and recognition nexus (MORN) motifs. MORN1 is highly conserved among apicomplexans. MORN1 specifically localizes to ring structures at the apical and posterior end of the inner membrane complex and to the centrocone, a specialized nuclear structure that organizes the mitotic spindle. Time-lapse imaging of tagged MORN1 revealed that these structures are highly dynamic and appear to play a role in nuclear division and daughter Cell Budding. Overexpression of MORN1 resulted in severe but specific defects in nuclear segregation and daughter Cell formation. We hypothesize that MORN1 functions as a linker protein between certain membrane regions and the parasite's cytoskeleton. Our initial biochemical analysis is consistent with this model. Whereas recombinant MORN1 produced in bacteria is soluble, in the parasite MORN1 was associated with the cytoskeleton after detergent extraction.
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plastid segregation and Cell division in the apicomplexan parasite sarcocystis neurona
Journal of Cell Science, 2005Co-Authors: Shipra Vaishnava, Daniel K Howe, Rajshekhar Y Gaji, David P Morrison, John M Murray, Rolf Entzeroth, Boris StriepenAbstract:Apicomplexan parasites harbor a secondary plastid that is essential to their survival. Several metabolic pathways confined to this organelle have emerged as promising parasite-specific drug targets. The maintenance of the organelle and its genome is an equally valuable target. We have studied the replication and segregation of this important organelle using the parasite Sarcocystis neurona as a Cell biological model. This model system makes it possible to differentiate and dissect organellar growth, fission and segregation over time, because of the parasite9s peculiar mode of Cell division. S. neurona undergoes five cycles of chromosomal replication without nuclear division, thus yielding a Cell with a 32N nucleus. This nucleus undergoes a sixth replication cycle concurrent with nuclear division and Cell Budding to give rise to 64 haploid daughter Cells. Interestingly, intranuclear spindles persist throughout the Cell cycle, thereby providing a potential mechanism to organize chromosomes and organelles in an organism that undergoes dramatic changes in ploidy. The development of the plastid mirrors that of the nucleus, a continuous organelle, which grows throughout the parasite9s development and shows association with all centrosomes. Pharmacological ablation of the parasite9s multiple spindles demonstrates their essential role in the organization and faithful segregation of the plastid. By using several molecular markers we have timed organelle fission to the last replication cycle and tied it to daughter Cell Budding. Finally, plastids were labeled by fluorescent protein expression using a newly developedS. neurona transfection system. With these transgenic parasites we have tested our model in living Cells employing laser bleaching experiments.
Stephen J Gould - One of the best experts on this subject based on the ideXlab platform.
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hiv pol inhibits hiv Budding and mediates the severe Budding defect of gag pol
PLOS ONE, 2012Co-Authors: Stephen J GouldAbstract:The prevailing hypothesis of HIV Budding posits that the viral Gag protein drives Budding, and that the Gag p6 peptide plays an essential role by recruiting host-Cell Budding factors to sites of HIV assembly. HIV also expresses a second Gag protein, p160 Gag-Pol, which lacks p6 and fails to bud from Cells, consistent with the prevailing hypothesis of HIV Budding. However, we show here that the severe Budding defect of Gag-Pol is not caused by the absence of p6, but rather, by the presence of Pol. Specifically, we show that (i) the Budding defect of Gag-Pol is unaffected by loss of HIV protease activity and is therefore an intrinsic property of the Gag-Pol polyprotein, (ii) the N-terminal 433 amino acids of Gag and Gag-Pol are sufficient to drive virus Budding even though they lack p6, (iii) the severe Budding defect of Gag-Pol is caused by a dominant, cis-acting inhibitor of Budding in the HIV Pol domain, and (iv) Gag-Pol inhibits Gag and virus Budding in trans, even at normal levels of Gag and Gag-Pol expression. These and other data support an alternative hypothesis of HIV Budding as a process that is mediated by the normal, non-viral pathway of exosome/microvesicle biogenesis.
Frederic Delbac - One of the best experts on this subject based on the ideXlab platform.
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toxoplasma gondii myosins b c one gene two tails two localizations and a role in parasite division
Journal of Cell Biology, 2001Co-Authors: Frederic Delbac, Astrid Sanger, Eva M Neuhaus, Rolf Stratmann, James W Ajioka, Catherine Toursel, Angelika Hermgotz, Stanisla Tomavo, Thierry SoldatiAbstract:In apicomplexan parasites, actin-disrupting drugs and the inhibitor of myosin heavy chain ATPase, 2,3-butanedione monoxime, have been shown to interfere with host Cell invasion by inhibiting parasite gliding motility. We report here that the actomyosin system of Toxoplasma gondii also contributes to the process of Cell division by ensuring accurate Budding of daughter Cells. T. gondii myosins B and C are encoded by alternatively spliced mRNAs and differ only in their COOH-terminal tails. MyoB and MyoC showed distinct subCellular localizations and dissimilar solubilities, which were conferred by their tails. MyoC is the first marker selectively concentrated at the anterior and posterior polar rings of the inner membrane complex, structures that play a key role in Cell shape integrity during daughter Cell biogenesis. When transiently expressed, MyoB, MyoC, as well as the common motor domain lacking the tail did not distribute evenly between daughter Cells, suggesting some impairment in proper segregation. Stable overexpression of MyoB caused a significant defect in parasite Cell division, leading to the formation of extensive residual bodies, a substantial delay in replication, and loss of acute virulence in mice. Altogether, these observations suggest that MyoB/C products play a role in proper daughter Cell Budding and separation.
Marc-jan Gubbels - One of the best experts on this subject based on the ideXlab platform.
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a toxoplasma morn1 null mutant undergoes repeated divisions but is defective in basal assembly apicoplast division and cytokinesis
PLOS ONE, 2010Co-Authors: Alexander Lorestani, Boris Striepen, Lilach Sheiner, Kevin Yang, Seth D Robertson, Nivedita Sahoo, Carrie F Brooks, David J P Ferguson, Marc-jan GubbelsAbstract:The membrane occupation and recognition nexus protein 1 (MORN1) is highly conserved among apicomplexan parasites and is associated with several structures that have a role in Cell division. Here we dissected the role of MORN1 using the relatively simple Budding process of Toxoplasma gondii as a model. Ablation of MORN1 in a conditional null mutant resulted in pronounced defects suggesting a central role for MORN1 in apicoplast segregation and in daughter Cell Budding. Lack of MORN1 resulted in double-headed parasites. These Janus-headed parasites form two complete apical complexes but fail to assemble a basal complex. Moreover, these parasites were capable of undergoing several more Budding rounds resulting in the formation of up to 16-headed parasites conjoined at the basal end. Despite this segregation defect, the mother's cytoskeleton was completely disassembled in every Budding round. Overall this argues that successful completion of the Budding is not required for Cell cycle progression. None of the known basal complex components, including a set of recently identified inner membrane complex (IMC) proteins, localized correctly in these multi-headed parasites. These data suggest that MORN1 is essential for assembly of the basal complex, and that lack of the basal complex abolishes the contractile capacity assigned to the basal complex late in daughter formation. Consistent with this hypothesis we observe that MORN1 mutants fail to efficiently constrict and divide the apicoplast. We used the null background provided by the mutant to dissect the function of subdomains of the MORN1 protein. This demonstrated that deletion of a single MORN domain already prevented the function of MORN1 whereas a critical role for the short linker between MORN domains 6 and 7 was identified. In conclusion, MORN1 is required for basal complex assembly and loss of MORN1 results in defects in apicoplast division and daughter segregation.
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a morn repeat protein is a dynamic component of the toxoplasma gondii Cell division apparatus
Journal of Cell Science, 2006Co-Authors: Marc-jan Gubbels, Shipra Vaishnava, Nico Boot, Jean Francois Dubremetz, Boris StriepenAbstract:Apicomplexan parasites divide and replicate through a complex process of internal Budding. Daughter Cells are preformed within the mother on a cytoskeletal scaffold, endowed with a set of organelles whereby in the final stages the mother disintegrates and is recycled in the emerging daughters. How the cytoskeleton and the various endomembrane systems interact in this dynamic process remains poorly understood at the molecular level. Through a random YFP fusion screen we have identified two Toxoplasma gondii proteins carrying multiple membrane occupation and recognition nexus (MORN) motifs. MORN1 is highly conserved among apicomplexans. MORN1 specifically localizes to ring structures at the apical and posterior end of the inner membrane complex and to the centrocone, a specialized nuclear structure that organizes the mitotic spindle. Time-lapse imaging of tagged MORN1 revealed that these structures are highly dynamic and appear to play a role in nuclear division and daughter Cell Budding. Overexpression of MORN1 resulted in severe but specific defects in nuclear segregation and daughter Cell formation. We hypothesize that MORN1 functions as a linker protein between certain membrane regions and the parasite's cytoskeleton. Our initial biochemical analysis is consistent with this model. Whereas recombinant MORN1 produced in bacteria is soluble, in the parasite MORN1 was associated with the cytoskeleton after detergent extraction.
Nozomu Okino - One of the best experts on this subject based on the ideXlab platform.
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sterylglucoside catabolism in cryptococcus neoformans with endoglycoceramidase related protein 2 egcrp2 the first steryl β glucosidase identified in fungi
Journal of Biological Chemistry, 2015Co-Authors: Takashi Watanabe, Hatsumi M Goda, Yohei Ishibashi, Tomofumi Miyamoto, Kazutaka Ikeda, Ryo Taguchi, Nozomu OkinoAbstract:Abstract Cryptococcosis is an infectious disease caused by pathogenic fungi, such as Cryptococcus neoformans and Cryptococcus gattii. The ceramide structure (methyl-d18:2/h18:0) of C. neoformans glucosylceramide (GlcCer) is characteristic and strongly related to its pathogenicity. We recently identified endoglycoceramidase-related protein 1 (EGCrP1) as a glucocerebrosidase in C. neoformans and showed that it was involved in the quality control of GlcCer by eliminating immature GlcCer during the synthesis of GlcCer (Ishibashi, Y., Ikeda, K., Sakaguchi, K., Okino, N., Taguchi, R., and Ito, M. (2012) Quality control of fungus-specific glucosylceramide in Cryptococcus neoformans by endoglycoceramidase-related protein 1 (EGCrP1). J. Biol. Chem. 287, 368–381). We herein identified and characterized EGCrP2, a homologue of EGCrP1, as the enzyme responsible for sterylglucoside catabolism in C. neoformans. In contrast to EGCrP1, which is specific to GlcCer, EGCrP2 hydrolyzed various β-glucosides, including GlcCer, cholesteryl-β-glucoside, ergosteryl-β-glucoside, sitosteryl-β-glucoside, and para-nitrophenyl-β-glucoside, but not α-glucosides or β-galactosides, under acidic conditions. Disruption of the EGCrP2 gene (egcrp2) resulted in the accumulation of a glycolipid, the structure of which was determined following purification to ergosteryl-3β-glucoside, a major sterylglucoside in fungi, by mass spectrometric and two-dimensional nuclear magnetic resonance analyses. This glycolipid accumulated in vacuoles and EGCrP2 was detected in vacuole-enriched fraction. These results indicated that EGCrP2 was involved in the catabolism of ergosteryl-β-glucoside in the vacuoles of C. neoformans. Distinct growth arrest, a dysfunction in Cell Budding, and an abnormal vacuole morphology were detected in the egcrp2-disrupted mutants, suggesting that EGCrP2 may be a promising target for anti-cryptococcal drugs. EGCrP2, classified into glycohydrolase family 5, is the first steryl-β-glucosidase identified as well as a missing link in sterylglucoside metabolism in fungi.