THE FINE STRUCTURE OF LEISHMANIA DONOVANI AND THE ROLE OF THE KINETOPLAST IN THE LEISHMANI-LEPTOMONAD TRANSFORMATION

Whole cell reconstructions of Leishmania mexicana through the cell cycle

The unicellular parasite Leishmania has a precisely defined cell architecture that is inherited by each subsequent generation, requiring a highly coordinated pattern of duplication and segregation of organelles and cytoskeletal structures. A framework of nuclear division and morphological changes is known from light microscopy, yet this has limited resolution and the intrinsic organisation of organelles within the cell body and their manner of duplication and inheritance is unknown. Using volume electron microscopy approaches, we have produced three-dimensional reconstructions of different promastigote cell cycle stages to give a spatial and quantitative overview of organelle positioning, division and inheritance. The first morphological indications seen in our dataset that a new cell cycle had begun were the assembly of a new flagellum, the duplication of the contractile vacuole and the increase in volume of the nucleus and kinetoplast. We showed that the progression of the cytokinesis furrow created a specific pattern of membrane indentations, while our analysis of sub-pellicular microtubule organisation indicated that there is likely a preferred site of new microtubule insertion. The daughter cells retained these indentations in their cell body for a period post-abscission. By comparing cultured and sand fly derived promastigotes, we found an increase in the number and overall volume of lipid droplets in the promastigotes from the sand fly, reflecting a change in their metabolism to ensure transmissibility to the mammalian host. Our insights into the cell cycle mechanics of Leishmania will support future molecular cell biology analyses of these parasites.

Leishmania highjack host lipid body for its proliferation in macrophages by overexpressing host Rab18 and TRAPPC9 by downregulating miR-1914-3p expression

Lipids stored in lipid-bodies (LBs) in host cells are potential sources of fatty acids for pathogens. However, the mechanism of recruitment of LBs from the host cells by pathogens to acquire fatty acids is not known. Here, we have found that Leishmania specifically upregulates the expression of host Rab18 and its GEF, TRAPPC9 by downregulating the expression of miR-1914-3p by reducing the level of Dicer in macrophages via their metalloprotease gp63. Our results also show that miR-1914-3p negatively regulates the expression of Rab18 and its GEF in cells. Subsequently, Leishmania containing parasitophorous vacuoles (Ld-PVs) recruit and retain host Rab18 and TRAPPC9. Leishmania infection also induces LB biogenesis in host cells and recruits LBs on Ld-PVs and acquires FLC12-labeled fatty acids from LBs. Moreover, overexpression of miR-1914-3p in macrophages significantly inhibits the recruitment of LBs and thereby suppresses the multiplication of parasites in macrophages as parasites are unable to acquire fatty acids. These results demonstrate a novel mechanism how Leishmania acquire fatty acids from LBs for their growth in macrophages.

Prenylquinones in Human Parasitic Protozoa: Biosynthesis, Physiological Functions, and Potential as Chemotherapeutic Targets

Human parasitic protozoa cause a large number of diseases worldwide and, for some of these diseases, there are no effective treatments to date, and drug resistance has been observed. For these reasons, the discovery of new etiological treatments is necessary. In this sense, parasitic metabolic pathways that are absent in vertebrate hosts would be interesting research candidates for the identification of new drug targets. Most likely due to the protozoa variability, uncertain phylogenetic origin, endosymbiotic events, and evolutionary pressure for adaptation to adverse environments, a surprising variety of prenylquinones can be found within these organisms. These compounds are involved in essential metabolic reactions in organisms, for example, prevention of lipoperoxidation, participation in the mitochondrial respiratory chain or as enzymatic cofactors. This review will describe several prenylquinones that have been previously characterized in human pathogenic protozoa. Among all existing prenylquinones, this review is focused on ubiquinone, menaquinone, tocopherols, chlorobiumquinone, and thermoplasmaquinone. This review will also discuss the biosynthesis of prenylquinones, starting from the isoprenic side chains to the aromatic head group precursors. The isoprenic side chain biosynthesis maybe come from mevalonate or non-mevalonate pathways as well as leucine dependent pathways for isoprenoid biosynthesis. Finally, the isoprenic chains elongation and prenylquinone aromatic precursors origins from amino acid degradation or the shikimate pathway is reviewed. The phylogenetic distribution and what is known about the biological functions of these compounds among species will be described, as will the therapeutic strategies associated with prenylquinone metabolism in protozoan parasites.

Dependency relationships between IFT-dependent flagellum elongation and cell morphogenesis in Leishmania

Flagella have multiple functions that are associated with different axonemal structures. Motile flagella typically have a 9 + 2 arrangement of microtubules, whereas sensory flagella normally have a 9 + 0 arrangement. Leishmania exhibits both of these flagellum forms and differentiation between these two flagellum forms is associated with cytoskeletal and cell shape changes. We disrupted flagellum elongation in Leishmania by deleting the intraflagellar transport (IFT) protein IFT140 and examined the effects on cell morphogenesis. Δift140 cells have no external flagellum, having only a very short flagellum within the flagellar pocket. This short flagellum had a collapsed 9 + 0 (9v) axoneme configuration reminiscent of that in the amastigote and was not attached to the pocket membrane. Although amastigote-like changes occurred in the flagellar cytoskeleton, the cytoskeletal structures of Δift140 cells retained their promastigote configurations, as examined by fluorescence microscopy of tagged proteins and serial electron tomography. Thus, Leishmania promastigote cell morphogenesis does not depend on the formation of a long flagellum attached at the neck. Furthermore, our data show that disruption of the IFT system is sufficient to produce a switch from the 9 + 2 to the collapsed 9 + 0 (9v) axonemal structure, echoing the process that occurs during the promastigote to amastigote differentiation.

Workshop no. 1. Alternate metabolic pathways in protozoan energy metabolism

The purpose of this workshop was to collect together colleagues investigating the intermediary metabolism of protozoa, with a view to discussing those pathways involved in energy metabolism and the production of ATP and other high-energy compounds, together with the factors affecting energy balance. The aspects of energy metabolism chosen for discussion comprised the metabolic pathways ranging from the strictly anaerobic to highly oxidative; subcellular compartmentation of these pathways within the protozoa; the functional role of these pathways including a consideration of aero-tolerance; and the use of inhibitors as biochemical probes and potential chemotherapeuticagents. Hopefully this approach has produced a broad 'over-view' of important areas of protozoan energy metabolism which will enable both the specialist and non-specialist to appreciate the similarities and differences between the metabolic behaviour of a range of protozoa.

Shape, form, function and Leishmania pathogenicity: from textbook descriptions to biological understanding

The shape and form of protozoan parasites are inextricably linked to their pathogenicity. The evolutionary pressure associated with establishing and maintaining an infection and transmission to vector or host has shaped parasite morphology. However, there is not a 'one size fits all' morphological solution to these different pressures, and parasites exhibit a range of different morphologies, reflecting the diversity of their complex life cycles. In this review, we will focus on the shape and form of Leishmania spp., a group of very successful protozoan parasites that cause a range of diseases from self-healing cutaneous leishmaniasis to visceral leishmaniasis, which is fatal if left untreated.

Characterization of mitochondrial bioenergetic functions between two forms of Leishmania donovani - a comparative analysis

Leishmaniasis is a growing health problem in many parts of the world partly due to drug resistance of the parasite. This study reports on the fisibility of studying mitochondrial properties of two forms of wild-type L. donovani through the use of selective inhibitors. Amastigote forms of L. donovani exhibited a wide range of sensitivities to these inhibitors. Mitochondrial complex II inhibitor thenoyltrifluoroacetone and FoF1-ATP synthase inhibitors oligomycin and dicyclohexylcarbodiimide were refractory to growth inhibition of amastigote forms, whereas they strongly inhibited the growth of promastigote forms. This result indicated that complex II and FoF1-ATP synthase were not functional in amastigote forms suggesting the presence of attenuated oxidative phosphorylation in the mitochondria of amastigote forms. In contrast, mitochondrial complex I inhibitor rotenone and complex III inhibitor antimycin A inhibited cellular multiplication and substrate level phosphorylation in amastigote forms, suggesting the role of complex I and complex III for the survival of amastigote forms. Further we studied the mitochondrial activities of both forms by measuring oxygen consumption and ATP production. In amastigote form, substantial ATP formation by substrate level phosphorylation was observed in NADPH-fumarate, NADH-fumarate, NADPH-pyruvate and NADH-pyruvate redox couples. None of the redox couple generated ATP formation was inhibited by FoF1-ATP synthase inhibitor oligomycin. Therefore, we may conclude that there are significant differences between these two forms of L. donovani in respect of mitochondrial bioenergetics. Our results demonstrated bioenergetic disfunction of amastigote mitochondria. Therefore, these alterations of metabolic functions might be a potential chemotherapeutic target.

Transformationin vitroofLeishmania mexicanaamastigotes to promastigotes: nutritional requirements and the effect of drugs

Anin vitrosystem is described in which over 85% of a population ofLeishmania mexicana mexicanaamastigotes transforms to promastigotes within 48 h. The differentiation process involves 3 morphologically and biochemically distinct intermediates, including a division stage. Cell division is shown to be necessary for complete development to promastigotes. Foetal calf serum (FCS) has been found to be an essential component of the medium for high percentage transformation to be achieved. One of the important components of the FCS has been identified as non-esterified fatty acids, and these support a relatively high percentage of amastigotes through transformation in the absence of FCS, possibly due to their use as energy substrates. Only small numbers of amastigotes transform to promastigotes if glucose or amino acids are the only energy substrates available. Transformation is inhibited by a number of metabolic inhibitors including anti-leishmanial and other anti-protozoal drugs. The stage at which inhibition is apparent varies with the inhibitor. It is suggested that the system described for the transformationin vitroofL. m. mexicanaamastigotes to promastigotes may be the best method available at present for studying the metabolism and drug sensitivity of amastigotes free from possible interference by host macrophage components.

The ultrastructure of the parasitophorous vacuole formed by Leishmania major

Protozoan parasites of Leishmania spp. invade macrophages as promastigotes and differentiate into replicative amastigotes within parasitophorous vacuoles. Infection of inbred strains of mice with Leishmania major is a well-studied model of the mammalian immune response to Leishmania species, but the ultrastructure and biochemical properties of the parasitophorous vacuole occupied by this parasite have been best characterized for other species of Leishmania. We examined the parasitophorous vacuole occupied by L. major in lymph nodes of infected mice and in bone marrow-derived macrophages infected in vitro. At all time points after infection, single L. major amastigotes were wrapped tightly by host membrane, suggesting that amastigotes segregate into separate vacuoles during replication. This small, individual vacuole contrasts sharply with the large, communal vacuoles occupied by Leishmania amazonensis. An extensive survey of the literature revealed that the single vacuoles occupied by L. major are characteristic of those formed by Old World species of Leishmania, while New World species of Leishmania form large vacuoles occupied by many amastigotes.

PLASTIDS AND MITOCHONDRIA: INHERITABLE SYSTEMS

Evidence has been cited which indicates that RNA and DNA are present in plastids and mitochondria. A multigenic apparatus in the plastid is deduced from the properties of bleached Euglena strains. Control mechanisms are present for the differentiation of proplastids to chloroplasts in Euglena and in higher plants, and for the differentiation of promitochondria to mitochondria in yeast. An operon-regulator mechanism for this control is suggested. A comparison of the hereditary cytoplasmic units of Euglena plastids and yeast mitochondria indicates cates great similarities in their properties. Because of these similarities in two unrelated organisms, we suggest that a DNA unit which is self-duplicating and which serves as a code for RNA is the basic hereditary unit of each plastid and mitochondrion. Much work must be done if this reasonable hypothesis is to be converted into well-founded theory. Some pressing problems await solution. We do not understand the nonrandom distribution of plastids in the mitotic divisions of variegated plants. A related unresolved problem is that of maternal inheritance, in which nonrandom segregation of cytoplasmic organelles occurs after fertilization, causing elimination of the organelles which are contributed by the male parent. How different are the gene components of one plastid in a cell from the gene components of other plastids in the same cell, and how do we test for these differences? Can gene exchange or recombination occur between organelles within the same cell? The answers to these questions may have to await development of more sophisticated techniques, such as the ability to transplant these organelles between different cells or to culture cellular organelles in vitro.

Detection of ubiquinone in parasitic and free-living protozoa, including species devoid of mitochondria

Ubiquinone (coenzyme Q, CoQ) was analyzed and individual homologues quantified in 11 species of parasitic and free-living protozoa by a combination of thin-layer chromatography and high performance liquid chromatography. Fast atom bombardment ionization-mass spectrometry was used for the first time to confirm the identity of the fractionated CoQ homologues and proved to be a fast, gentle and convenient method for ubiquinone identification. Ubiquinone was detected in all organisms including those devoid of identifiable mitochondria. However, significantly lower levels of CoQ were present in those organisms lacking this respiratory organelle (5- to 50-fold lower in Entamoeba histolytica (CoQ9) and 15- to 350-fold for Giardia lamblia (CoQ9) and Tritrichomonas foetus (CoQ10)). Coenzyme Q9 was the predominant homologue in promastigotes of Leishmania donovani and Leishmania major. Lower amounts of CoQ8 and CoQ10 were also detected in L. donovani, and CoQ8 in L. major. Comparison of the in vitro cultivated promastigote and amastigote forms of Leishmania pifanoi and Leishmania amazonensis revealed CoQ9 to be the sole detectable ubiquinone homologue in the amastigote (macrophage) stage, whereas CoQ8 and CoQ10 were also present in the promastigotes (life cycle stage found in the insect gut) of L. pifanoi, and CoQ7 and CoQ8 in promastigotes of L. amazonensis. Interestingly, the total amounts of CoQ were similar in both forms of these organisms. The free-living ciliates, Tetrahymena thermophila and Paramecium tetraurelia contained CoQ8 as the predominant ubiquinone species and this homologue was also present in the isolated cilia from P. tetraurelia. The marine ciliate, Parauronema acutum contained CoQ7 as well as CoQ8. Comparison of xenosome-containing P. acutum with organisms lacking the symbiont revealed that twice the level of CoQ8 was present in cells grown with this cytoplasmic gram-negative bacterium. Results suggest that CoQ is ubiquitous amongst the protozoa, regardless of the presence of mitochondria, and may function in alternative roles to that of mitochondrial electron transport chain component.

Interaction of small ribosomal and transfer RNAs with a protein from Leishmania donovani

Using synthetic antisense RNA from the 5'-untranslated region of the beta-tubulin gene as probe in gel retardation assays, a heat stable RNA-binding factor was identified in promastigotes of the kinetoplastid protozoan Leishmania donovani. The same or similar factors interact with several small ribosomal RNA (srRNA) species and, more weakly, with tRNA, as shown by binding and competition experiments. Deletion analysis indicated involvement of repeated purine-rich motifs on the antisense RNA, in the reaction. Related, conserved motifs occur on at least two of the srRNAs. By a modified Western blot assay, the RNA-binding species was identified as a single, small polypeptide. The activity is apparently specific for the promastigote stage of the parasite, being undetectable in amastigotes. The properties of this RNA-binding factor suggest that it is a novel, previously uncharacterized protein.

Interaction of drugs with extranuclear genetic elements and its consequences

Bacterial ancestry of mitochondria and plastids is now generally accepted. Both organelles contain their own DNA and transcription-translation apparatus of a prokaryotic type. Due to this fact these systems carry bacteria-like properties. Thus organellar DNA and ribosomes are essentially different from nuclear DNA and cytoplasmic ribosomes in physical as well as in functional respects. Due to the bacterial character of both types of organelles they are susceptible to various antibacterial chemicals. Inhibitors of bacterial protein synthesis inhibit mitochondrial (plastidial) biogenesis. Therefore the cellular content of mitochondria (plastids)-made proteins decreases during cytoplasmic turnover or cell division in the presence of these drugs. Such drug activity consequently leads to a reduced capacity for oxidative phosphorylation or photosynthesis. Organellar genomes are less stable and more sensitive to mutagenesis as compared to nuclear genome. It means also that genotoxic agents induce various disorders of mitochondrial (plastidial) functions. Impairments in the respiratory chain are associated with structural as well as functional abnormalities of mitochondria. These are clinically expressed mostly in tissues with a high demand for ATP: brain, heart, skeletal muscle, and retina. On the other hand, some antibacterial inhibitors of mitochondrial biogenesis (e.g., tetracyclines) inhibit selectively tumor cell proliferation. Therefore they may be considered for use in anticancer therapy. The article summarizes the response of mitochondria and plastids in various organisms to drugs and environmental xenobiotics. Various model organisms suitable for detection of xenobiotic effect on mitochondria (plastids) are presented as well as the possible consequences of such interaction.

Carbon dioxide abolishes the reverse Pasteur effect in Leishmania major promastigotes

The products released by Leishmania major promastigotes incubated with [1-13C]glucose as sole exogenous carbon source were identified using nuclear magnetic resonance (NMR). Under aerobic (95% O2/5% CO2) conditions, acetate, succinate, and small amounts of pyruvate, D-lactate, and glycerol were released in addition to CO2. Under anaerobic (95% N2/5% CO2) conditions, the relative amounts of products formed changed and alanine was also released. The changes in the rates of glucose consumption and product formation during the aerobic to anaerobic transition were measured. Under hypoxic conditions (O2 less than 0.2%), glucose consumption was decreased by about 50%. Under completely anaerobic conditions (100% N2), glucose consumption almost ceased (a total reverse Pasteur effect). The inclusion of 5% CO2 in the gas phase restored hypoxic and anaerobic glucose consumption to the aerobic rate, and increased production of succinate, pyruvate, and D-lactate. Thus, CO2 and very low concentrations of O2 have strong regulatory effects on L. major glucose metabolism. A quantitative carbon balance showed that the NMR-identified products accounted for only about 25% of the glucose carbons consumed under aerobic conditions. CO2, measured as the release of 14CO2 from [U-14C]glucose, accounted for an additional 25% of the glucose consumed. About 11% of the glucose carbon was incorporated into trichloroacetic acid-insoluble products, mostly lipid. Large amounts of label from [U-14C]glucose were incorporated into the intracellular pools of alanine, glutamate, glutamine, and aspartate, indicating that CO2 from unlabeled amino acids contributed to the carbon balance. Under anaerobic conditions, all the glucose carbons consumed could be accounted for solely by the NMR-identified products.

Oxidation of fatty acids by Leishmania braziliensis panamensis

Heating cultures of Leishmania braziliensis panamensis (grown at 26 degrees C) to 34 degrees C for 1.5-12 h transformed the cells to an ellipsoidally shaped form. The heat treatment caused an increase in the rate of oxidation of both medium and long chain fatty acids but decreased the rate of oxidation of [1-14C]glucose. The rate of fatty acid oxidation continued to increase for times as long as 20 h after returning the cultures to 26 degrees C. In both the promastigote and heat-induced ellipsoidal forms, the ratio of 14CO2 release from [1-14C]laurate to that from [12-14C]laurate was generally larger than four, whereas this ratio from [1-14C]oleate relative to [10-14C]oleate was approximately two. These data show that metabolic and morphological differentiation begin after a short heat treatment and that some metabolic changes may continue even after the reverse transformation is initiated. The data also suggest that either the omega-terminal portion of the fatty acids is not completely oxidized to acetyl CoA and/or that there are two functional fatty acid oxidation pathways in Leishmania.

Ultrastructure of bone marrow in patients with visceral leishmaniasis

Ultrastructural studies were performed on bone marrow aspirates from three patients with visceral leishmaniasis. The patients were moderately anaemic but showed a suboptimal increase in the absolute reticulocyte count. Serum and red cell folate concentrations and serum vitamin B12 concentrations were normal in all three cases, and serum ferritin concentrations were normal or increased. The bone marrows were hypercellular and showed erythroid hyperplasia; a high proportion of the erythroblasts showed dyserythropoietic changes. Amastigote forms of Leishmania donovani were found within bone marrow macrophages and within occasional neutrophil and eosinophil granulocytes. Electron microscopy showed the presence of many abnormal cells, which probably represented immature erythroblasts with giant lysosomes. These cells were often large, usually contained immature nuclei with relatively little condensed chromatin, had 1-20 electron dense cytoplasmic granules with an average diameter of 0.5 micron, and regularly displayed substantial rhopheocytotic activity. A few abnormal cells and intermediate and late erythroblasts appeared to have been phagocytosed by macrophages. The data indicate that dyserythropoiesis and ineffective erythropoiesis have a role in the pathogenesis of the anaemia of at least some cases of kala-azar.

Leishmania mexicana: comparative fine structure of amastigotes and promastigotes in vitro and in vivo

Amastigotes of Leishmania mexicana pifanoi were cultivated by serial transfers in cell-free medium UM-54 at 33 and 35 C. Electron microscopy was used to analyze the structural relationships among promastigotes, axenically cultured amastigotes, and amastigotes in footpads of infected hamsters. These studies revealed very close structural similarities between culture and hamster derived amastigotes. However, both of these amastigotes differed from the promastigotes in the following aspects. The flagellum of promastigotes contained a paraxial rod originating at the axosome level within the flagellar pocket, whereas the flagellum of amastigotes lacks this structure. The flagellar pocket of promastigotes was usually small whereas amastigotes had a distended reservoir. Subpellicular microtubules of promastigotes terminated at the posterior end, whereas those of amastigotes ended subterminally. Membrane bounded vesicles were present only in amastigotes. These results along with the biologic and antigenic comparisons indicate that amastigotes obtained from axenic cultures are related very closely to amastigotes from infected hamster footpads and that their relationship to promastigotes is far more distant.

A study of the sensitivity of Leishmania donovani promastigotes and amastigotes to hydrogen peroxide. II. Possible mechanisms involved in protective H2O2 scavenging

Different hydrogen peroxide (H2O2)-scavenging mechanisms, and the conditions under which they operate, have been examined in promastigotes and amastigotes of Leishmania donovani. For promastigotes, the ability of the parasite to remove H2O2 was completely ablated by sonication whereas for sonicated amastigotes substantial loss of H2O2 from the phagocyte-free test system still occurred. In direct contrast, the ability of amastigotes, but not promastigotes, to remove H2O2 was markedly inhibited by aminotriazole or sodium azide. This suggested a role for haem-containing enzymes, catalase or peroxidases, as a protective H2O2-scavenging mechanism and was consistent with detection of catalase in amastigotes but not promastigotes using a spectrophotometric assay. Both forms of the parasite did, however, show reduced ability to remove H2O2 at 5-7 degrees C indicating that additional enzymatic scavenging mechanisms may operate. Glutathione peroxidase activity was undetectable in either form of the parasite. The total thiol sink, glutathione (GSH) plus protein thiols, was greater in promastigotes but the ability to regenerate GSH via glutathione reductase was equivalent for promastigotes and amastigotes. Less temperature-dependent non-enzymatic mechanisms (e.g. an unsaturated lipid sink) also appear to contribute to removal of H2O2 by both promastigotes and amastigotes. It seems likely, nevertheless, that the difference in H2O2 sensitivity between the two forms of the parasite relates to the activity of the direct H2O2-scavenging enzyme, catalase, which appears to operate more efficiently against a bolus of reagent H2O2.

Electron microscopy of Leishmania donovani in splenic aspirates from patients with visceral leishmaniasis during treatment with sodium stibogluconate

Studies were made of the ultrastructure of amastigotes of Leishmania donovani before and during treatment of patients with sodium stibogluconate. The most consistent effects of treatment on the amastigotes were a reduction in average size, greater irregularity of the cell outline, and a moderate increase in the electron density of the cytoplasm associated with a greater concentration of ribosomes. It is suggested that the drug affects active transport functions or permeability of the plasma membrane.

Monoclonal antibodies recognizing determinants specific for the promastigote state of Leishmania mexicana

Two monoclonal antibodies (IX-IF9-D8 and IX-5H9=C1) produced to a membrane enriched fraction of Leishmania mexicana amazonensis promastigotes have been demonstrated to be specific for the promastigote (insect) form and not the amastigote (mammalian host) form of the parasite. The antigens recognized by these monoclonal antibodies are not found on amastigotes isolated from infected animals or on amastigotes isolated from a macrophage cell line J774 infected initially with promastigotes. The antigens are not re-expressed by amastigotes cultured at 34 degrees C; however, amastigotes cultured at 24 degrees C that have begun transformation into promastigotes do express these antigens. The level of expression of these antigens in cultures of amastigotes undergoing transformation into promastigotes, increases with time from 16 to 36 h and appears to correlate with the percentage of promastigotes. Two protein molecules with apparent molecular weights of 40,000 and 92,000 have been identified by radioimmune precipitation as associated with L. mexicana promastigote stage specific determinants.

Tubulin biosynthesis in the developmental cycle of a parasitic protozoan, Leishmania mexicana: changes during differentiation of motile and nonmotile stages

Cytodifferentiation in the transition cycle of the parasitic protozoan Leishmania mexicana amazonensis was studied in vitro. The flagellated motile promastigotes transform into the nonmotile amastigotes in 7 days at 35 degrees C intracellularly in the murine macrophage line J774G8. In medium 199 plus fetal bovine serum, the reverse transformation occurs extracellularly at 27 degrees C in 2 days. Slab gel electrophoresis of leishmanias labeled with [35S]methionine during transformation revealed changes in protein banding patterns. The intensity of two protein species with apparent molecular weights of approximately equal to 55,000 increased in the amastigote-to-promastigote differentiation and decreased during the reverse transformation. These two protein species comigrated approximately with alpha- and beta-tubulin of Chlamydomonas flagella in two-dimensional gel electrophoresis. The lower band was further identified as beta-tubulin by immunoprecipitation using rabbit antiserum specific to the beta-tubulin of Chlamydomonas axonemes. The biosynthetic change of tubulin was found to correlate with the morphological change of microtubules is leishmanial flagella and cytoskeleton during transformation.

Respiration of Leishmania mexicana amastigotes and promastigotes

Promastigotes of Leishmania mexicana mexicana recently derived from amastigotes by transformation in vitro respired at a rate (17 nmol O2/min per 10(8) parasites) 4-5 times higher than that of amastigotes, but when the difference in cell protein content between the two preparations was taken into account the rates were not significantly different (32 nmol O2/min per mg protein). The respiration of both amastigotes and promastigotes was sensitive to cyanide, azide, antimycin A, 2-n-heptyl-4-hydroxyquinoline-N-oxide and high concentrations of amytal, but insensitive to rotenone and salicyl-hydroxamic acid, indicating that the two developmental forms possess a similar cytochrome-containing respiratory chain. D-Glucose and non-esterified fatty acids stimulated promastigote respiration and amastigote transformation to promastigotes in vitro; possibly these substances are important exogenous energy substrates for both forms of the parasites. Amino acids (incuding L-proline) and proteins did not appear to be used as energy substrates. The respiration rate of promastigotes was found to rise significantly upon continued sub-culture in vitro; at the same time cell size and protein content increased.

Leishmania mexicana amazonensis: attachment to the membrane of the phagocytic vacuole of macrophages in vivo

Intracellular forms of Leishmania mexicana amazonensis divide inside the phagocytic vacuole of macrophages. Some parasites attach to the membrane of the phagocytic vacuole while others remain free in the vacuole. Examination of thin sections of the attachment region by electron microscopy revealed a space of 2 nm between the membrane of the phagocytic vacuole and the plasma membrane of the parasite. Freeze-fracture replicas showed an array of intramembranous particles in some areas of the parasite's plasma membrane resembling a gap junction which, in other cells, is involved in the process of intracellular communication.

Incorporation of [1-14C]octadecanol into the lipids of Leishmania donovani

After incubation of stationary phase Leishmania donovani with [1-14C]octadecanol, about 70% of the precursor was taken up within 3 hr. Wax esters and acyl moieties of glycerolipids contained most of the 14C-activity from 3 to 6 hr, because octadecanol was partly oxidized to stearate. Ether moieties were only weakly labeled. After 40 hr, 1-0-alkyl and 1-0-alk-1'-enyl diacylglycerols as well as 1-0-alkyl and 1-0-alk-1'-enyl-2-acyl-sn-glycero-3-phosphoethanolamines contained nearly all of the radioactivity. Most of the label in the neutral ether lipids was located in the alkyl ether side chain, whereas, in the phosphatidylethanolamine fraction, most of the label was found in the alkenyl ether side chain. Administration of 1-0-[1-14C]hexadecyl glycerol resulted in rapid labeling of the vinyl ether side chain of phosphatidylethanolamine plasmalogen (1 hr) increasing further at 2.5 hr. Most of the radioactivity in the alkoxy diacylglycerols was found in the 1-0-alkyl moiety.

Studies on the ultrastructure, virus-like particles and infectivity of Leishmania hertigi

Five strains of Leishmania hertigi hertigi isolated in Panama and three strains of L. hertigi deanei isolated in Brazil were studied. Ultrastructural examination of promastigotes grown in culture showed virus-like particles (VLPs), 55--60 nm diameter, in the cytoplasm of all strains. The VLPs were normally either organized in paracrystalline clusters or associated with induced tubules. In some cases the VLPs were associated with dense vesicular bodies. Mitochondria with which the VLPs were associated had enlarged elongate or circular cristae. Elongate 'microbodies' containing rod-like structures were observed in promastigotes grown in culture. Poor infections of promastigotes developed in the midguts of 10% of laboratory-bred Lu. longipalpis following experimental feeding on cultures of L. h. hertigi. VLPs were seen in a promastigote in the midgut of a sandfly five days after feeding. Laboratory mammals proved poor hosts for L. hertigi. Cryptic infections in the visceral organs of immunosuppressed hamsters and immunodeficient 'nude' mice were detectable only by culture. Infections of DS cell and mouse peritoneal macrophage cultures showed amastigotes with a high ribosomal density and deep invaginations of the pellicular layer. VLPs were rarely seen in these amastigotes.

Mitochondrial framework (reticulum mitochondriale) in rat diaphragm muscle

Reconstitution of rat diaphragm mitochondria has been carried out with the use of the serial section technique. It is shown that mitochondrial material is organized as networks transpiercing the I band regions of the muscle near the Z-discs. Each network forms tubules, oriented perpendicular to its plane, and branches, connecting the network with mitochondrial clusters in the fiber periphery. Such a system, defined as mitochondrial reticulum, is found to be characteristic of the diaphragm of adult animals. It is absent in the diaphragm of rat embryos and newborn rats. The junctions of the branches of mitochondrial reticulum are described. In the junction site, the outer membranes of two mitochondrial branches are in contact, and spaces between outer and inner membranes are filled with an osmiophilic substance. No junctions were found in the embryos and in newborn animals whose diaphragm contains single, elliptical or worm-like mitochondria. The hypothesis is put forward that the mitochondrial reticulum serves as a system for transport of energy, oxygen and fatty acid residues along mitochondrial membranes over distances commensurable with the muscle fiber diameter.

Leishmania donovani. Hamster macrophage interactions in vitro: cell entry, intracellular survival, and multiplication of amastigotes

An in vitro system was developed for studying host-parasite cellular interactions in visceral leishmaniasis with amastigotes isolated from infected spleens of hamsters and their peritoneal macrophages maintained by an improved method. The culture system supports the growth of Leishmania donovani amastigotes with different parasite/macrophage ratios for up to 2 wk, yielding results more consistent and reproducible than previously possible. Results indicated that the "forms" of the amastigotes (with or without adherent host membranes) and the "state" of the macrophages (with or without stimulation in vivo by thioglycollate or in vitro by aging) had no effect on the growth rate of the parasites, which, however, seems to vary with the macrophage subpopulations. An electron microscope study suggests that amastigotes are ingested through phagocytosis by the macrophages and become lodged in loose phagosomes. Additional evidence with quantitative data is presented to support the earlier findings that phagosome-lysosome fusion occurs after the interiorization of the parasites and that they not only survive but multiply in these vacuoles. During the postinfection periods, reorientation of amastigotes in vacuolar space results in the appearance of three types of parasitophorous vacuoles (parasites in loose vacuoles, in tight-fitting vacuoles or abutting in part against the inner lining of vacuoles). The last category may be the predominant type giving rise to the variations observed. Exogenously introduced dense marker accumulated in these parasitophorous vacuoles of the macrophages infected for several days indicating a continuous accessibility of amastigotes to the ambient mestruum via phagosome-lysosome vacuolar system of the host cells. This finding may have significant implications in parasite nutrition, host immunity, and chemotherapy of leishmaniasis.

Unusual axonemal doublet arrangements in the flagellum of Leishmania amastigotes

Studies on the fine structure of Leishmania mexicana, L. enriettii and L. tropica major have revealed several unusual arrangements of microtubules in the flagellar axoneme. The anterior end of the flagellum in these three species was found to contain disarranged axonemal doublets (d) in the absence of the two central singlets(s). Leishmania amastigotes do not use their flagellum as do promastigotes for propulsion, and persistence of the usual 9d and 2s microtubular arrangement may not be necessary.

Promotion of leishmanial infections in non-permissive host macrophages by conditioned medium

Leishmania enriettii grows well in guinea pig macrophages in culture but fails to do so in mouse macrophages. Dialyzed and concentrated conditioned medium from L. enriettii cultures promoted the infection in the mouse macrophages at 37 degrees C and at 32 degrees C. Similarly processed medium on which L. tropica had been cultured did not cause the same effect. Immune precipitation of the conditioned medium by anti-Leishmania serum cancelled out the effect. Infections of guinea pig macrophages by L. tropica were also enhanced by the homologous medium, but we were unable to quantitate the effect.