摘要:

ABSTRACTThe large, free‐living amoebae have been widely used as model cells for studying a variety of biological phenomena, including cell motility, nucleocytoplasmic interactions, membrane function, and symbiosis. Results of studies by our group on amoebae as moving cells, as material for micrurgical manipulations, and as hosts for intracellular symbionts are summarized here. In particular, our recent studies of the amoeba as a microcosm, in which spontaneously infecting foreign microbes have become integrated as necessary cell components, are described in some detail. These processes have involved an initial microbial infection, mutual adaptation by the host and symbionts, and development of obligatory symbiosis. Evidence is presented to show that symbiont‐derived macromolecules are involved in the protection of symbionts from digestion, the symbionts have acquired regulatory elements on their chromosomal genes to enhance production of beneficial gene products, and symbionts apparently utilize host‐derived macromolecules to their benefit. These studies involved morphological observations both at light and electron microscopic levels, physiological and genetic studies, production and use of poly‐ and monoclonal antibodies, and molecular‐biological approaches including gene cloning and sequencing. It is shown that amoebae are uniquely suited as model cells with which to study these

ISSN:1066-5234    

DOI:10.1111/j.1550-7408.1995.tb01532.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTOchromonas danica,a freshwater, planktonic chrysophyte, is capable of sensing the light conditions of its environment. This biflagellate alga has a swelling near the base of the short flagellum and a chloroplastidic stigma in close association with it. A procedure is described for the isolation of this three dimensional flagellar swelling, the presumed photoreceptor. In contrast to an earlier method developed for the isolation of the paraflagellar swelling fromEuglena gracilis,the protocol reported here forOchromonasresults in higher yields that should facilitate future biochemical investigations and could open avenues of investigation for the isolation and purification of the presumptive receptor protein. To verify the hypothesis that a rhodopsin‐like protein might be present in this alga, we applied a standard extraction procedure successfully used in the identification of retinal. We here report the purification and identification of all‐trans retinal inOchromonascells by column chromatography, HPLC and GC‐MS. Since retinal is the chromophore of rhodopsin‐like proteins, this finding may suggest that in these unicellular algae, too, a rhodopsin‐like protein could be the photorecepto

ISSN:1066-5234    

DOI:10.1111/j.1550-7408.1995.tb01533.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTGenes encoding the TFIID TATA‐box binding protein (TBP) from two probable species of ratPneumocystis carinii(prototype and variant) were sequenced. The twoP. cariniiTBP gene sequences were 91% identical to each other, and 65‐77% identical to TBP genes from other species. A cDNA from one of the twoP. cariniiTBP genes was sequenced, which showed that four small introns resided in identical positions within the TBP genes from the prototype and variant ratP. carinii.Conservation of the 180 amino acids that constitute the conserved core of TBP was 97% between theP. cariniiTBP, which were 95% and 97% identical to conserved core sequences of TBP fromSaccharomyces cerevisiaeandSchizosaccharomyces pomberespectiv

ISSN:1066-5234    

DOI:10.1111/j.1550-7408.1995.tb01534.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTPrevious investigations have shown that the adhesion ofT. cruziplasma membrane vesicles (PMV) to monolayers of host cell myoblasts and to immobilized heart muscle sarcolemma membranes (PAM) on polyaerylamide beads is mediated by the interaction ofT. cruziattachment sites with the muscarinic cholinergic and β‐adrenergic receptors of the host cell membrane. It has also been shown that this interaction is blunted by the specific antagonists of the mammalian receptors atropine and propranol, respectively. In the studies reported here, PAM also rapidly attached to swimmingT. cruzitrypomastigotes in a complex, concentration‐dependent fashion and binding isotherms showed that the equilibrium between free and bound PAM is rapidly reached within 2 minutes of incubation in physiologically balanced salt solutions. In this time frame, trypomastigote cAMP levels are significantly reduced from steady state values within 30 seconds of the addition of PAM in a buffer system containing a diesterase inhibitor. Maximal attenuation of cAMP levels was measured between 1 and 2 minutes of the addition of PAM toT. cruzitrypomastigotes. The degree of cAMP level attenuation was reduced by blocking PAM attachment with either atropine or propranol. On the basis of these results we propose that a likely pathway for the negative parasite signal generated upon adhesion of host muscle cell membranes to the surface of the flagellates is from the parasite's surface attachment sites directly to a Pertussis toxin sensitive inhibitory protein Gi, thereby blunting adenyl cyclase activity and cAMP forma

ISSN:1066-5234    

DOI:10.1111/j.1550-7408.1995.tb01535.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTPneumocystis cariniiis an opportunistic agent found in the lung of various mammals which often causes severe pneumonia in immunocompromised humans, especially in AIDS patients. In the past several years significant additions have been made to the collection of knowledge we have concerning the genetic diversity ofP. carinii.These additions provide new understanding ofPneumocystistransmission and the effect of possible reservoirs ofPneumocystisin the various species. In this study, a 400‐bp fragment of the thymidylate synthase (TS) gene ofP. cariniihas been amplified by PCR from 43 parasite isolates obtained from 4 mammalian host species: rat, mouse, rabbit and human. A probe selected from the TS gene sequence of rat‐derivedP. cariniiwas hybridized with the amplified products from rat‐ and mouse‐derivedP. carinii, but not with rabbit or humanP. cariniiDNA. Restriction profiles were performed on amplified fragments from all isolates, and the 4 nucleotide sequences of the TS gene fragment amplifed from rat, mouse, rabbit and humanP. cariniiwere determined. Differences were detected in the gene fragment inP. cariniiisolates from the 4 host species; however no difference was revealed inP. cariniiisolates within a single host species, whatever the host strain or its geographic origin. Thus, the sequence differences of theP. cariniiTS gene appeared as host‐species specific. A specific probe which recognized all humanP. cariniiisolates wa

ISSN:1066-5234    

DOI:10.1111/j.1550-7408.1995.tb01536.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTSite‐directed mutagenesis of the telomerase RNA fromTetrahymena thermophilawas used previously to demonstrate the templating function of a sequence within this RNA; this sequence specifies the sequence of telomeric DNA in vivo. The possible functional importance of a phylogenetically conserved nucleotide outside the telomerase RNA template region was investigated by a similar experimental approach. The telomerase RNA gene was altered by site‐directed mutagenesis, cloned in a circular selectable transformation vector consisting of an rRNA gene carrying a selectable drug resistance marker, and introduced into macronuclei of vegetatively dividingTetrahymena thermophilaby microinjection. Changing an invariant A to U at position 16 of the telomerase RNA (A16U) had no effect detectable by phenotype on telomerase function in vivo. However these experiments showed that a telomerase template alteration that dictates the synthesis of the mutant telomeric DNA sequence GGGGTC leads to a profound change in the population of rDNA replicons. The addition of GGGGTC mutant repeats leads to selective pressure for the loss of high copy linear rDNA, and the rRNA genes are maintained in the form of the circular rDNA replicons introduced during transformat

ISSN:1066-5234    

DOI:10.1111/j.1550-7408.1995.tb01537.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTTwo distinct sequevars, denoted Pc1 and Pc2, of the opportunistic pathogenPneumocystis cariniihave been previously identified based on the sequence of their 26S rRNA genes, the location of group I self‐splicing introns and pulsed field electrophoretic patterns of chromosomal DNA. This study shows that the sequences of 16S and 5.8S rRNA genes also vary between these sequevars, and that greater variation was seen in the internal transcribed spacer regions. Polymerase chain reaction and restriction analysis can distinguish between these sequevar

ISSN:1066-5234    

DOI:10.1111/j.1550-7408.1995.tb01538.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTMorphology and morphogenesis ofOnychodromus grandis(Hypotrichida, Ciliata) were studied in vivo and in protargolimpregnated preparations. The species was isolated from halophyte communities in astatic shallow waters of the Hortobágy National Park, Hungary. The species has two well developed dorsal horns. According to some characteristics (number and situation of ventral cirri) our findings differ from Stein's description in 1859. Individuals of the population studied had 9 ventral cirri in 3 rows. Nine rows of dorsal kineties were found on the back. It was found that the oral primordium develops in the vicinity of the transverse cirri. InO. grandismarginal primordia are formed in the marginal rows with the participation of parental cirri. This is also true forLaurentiella acuminata.Dorsal fragmentation ofO. grandisdisplays similarity to that ofL. acuminata, considering especially the development of the numerous small dorso‐marginal kineties. There are certain similarities amongO. quadricornutus, O. indica, L. acuminata, Stylonychia voraxandO. grandisin the development of the ventral and dorsal pattern and in some morphogenetical events. The remarkable differences in the interphase cells can be related simply to the significantly different numbers of cortical units (number of cirri). and also to the various cell siz

ISSN:1066-5234    

DOI:10.1111/j.1550-7408.1995.tb01539.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTTrifluralin, a herbicide which is known to bind to plant and algal tubulin, induced ultrastructural changes in the microtubules of the maturePlasmodium falciparumgametocytes in vitro. Trifluralin treatment led to disassembly of the well ordered subpellicular microtubules, whereas it had no effect on microtubules of human platelets or of rat neuronal cells in vitro. The disassembled microtubules showed fragmented large tubular structures, which frequently were associated with the pellicular membranes. Electron microscopic autoradiography showed radioactive trifluralin associated with the microtubule fragments. These results provide evidence that trifluralin selectively binds to microtubules in malaria parasites and causes disruption of their structure.

ISSN:1066-5234    

DOI:10.1111/j.1550-7408.1995.tb01540.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTThe Rhizopoda comprise a diverse assemblage of protists which depend on lobose or filose pseudopodia for locomotion. The biochemical and morphological diversity of rhizopods has led to an uncertain taxonomy. Ribosomal RNA sequence comparisons offer a measure of evolutionary relatedness that is independent of morphology and has been used to demonstrate a polyphyletic origin of the Lobosea. We sequenced complete small subunit ribosomal RNA coding regions from the filose amoebae,Euglypha rotundaandPaulinella chromatophora(Euglyphina) to position these taxa in the eukaryote phylogeny. The neighbor‐joining analyses show thatE. rotundaandP. chromatophorashare a monophyletic origin and are not closely related to any lobose amoebae in our analyses. Instead, the Euglyphina form a robust sister group to the Chlorarachniophyta. These results provide further evidence for the polyphyly of the Rhizopoda and support the creation of a new amoeboid lineage which includes the Euglyphina and the chlorarachniophyte algae; taxa with tubular mitochondrial cristae and filose or reticulate pseudopodi

ISSN:1066-5234    

DOI:10.1111/j.1550-7408.1995.tb01541.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY