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41.
Sequence variations in small-subunit ribosomal RNAs of Hartmannella vermiformis and their phylogenetic implications 总被引:1,自引:0,他引:1
Evidence of associations between free-living amoebas and human disease has
been increasing in recent years. Knowledge about phylogenetic relationships
that may be important for the understanding of pathogenicity in the genera
involved is very limited at present. Consequently, we have begun to study
these relationships and report here on the phylogeny of Hartmannella
vermiformis, a free-living amoeba that can harbor the etiologic agent of
Legionnaires' disease. Our analysis is based on studies of small-subunit
ribosomal RNA genes (srDNA). Nucleotide sequences were determined for
nuclear srDNA from three strains of H. vermiformis isolated from the United
Kingdom, Germany, and the United States. These sequences then were compared
with a sequence previously obtained for a North American isolate by J. H.
Gunderson and M. L. Sogin. The four genes are 1,840 bp long, with an
average GC content of 49.6%. Sequence differences among the strains range
are 0.38%-0.76%. Variation occurs at 19 positions and includes 2
single-base indels plus 14 monotypic and 3 ditypic single-base
substitutions. Variation is limited to eight helix/loop structures
according to a current model for srRNA secondary structure. Parsimony,
distance, and bootstrap analyses used to examine phylogenetic relationships
between the srDNA sequences of H. vermiformis and other eukaryotes
indicated that Hartmannella sequences were most closely related to those of
Acanthamoeba and the alga Cryptomonas. All ditypic sites were consistent
with a separation between European and North American strains of
Hartmannella, but results of other tests of this relationship were
statistically inconclusive.
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42.
Cell-to-cell transfer of glial proteins to the squid giant axon: The glia- neuron protein transfer hypothesis
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The hypothesis that glial cells synthesize proteins which are transferred to adjacent neurons was evaluated in the giant fiber of the squid (Loligo pealei). When giant fibers are separated from their neuron cell bodies and incubated in the presence of radioactive amino acids, labeled proteins appear in the glial cells and axoplasm. Labeled axonal proteins were detected by three methods: extrusion of the axoplasm from the giant fiber, autoradiography, and perfusion of the giant fiber. This protein synthesis is completely inhibited by puromycin but is not affected by chloramphenicol. The following evidence indicates that the labeled axonal proteins are not synthesized within the axon itself. (a) The axon does not contain a significant amount of ribosomes or ribosomal RNA. (b) Isolated axoplasm did not incorporate [(3)H]leucine into proteins. (c) Injection of Rnase into the giant axon did not reduce the appearance of newly synthesized proteins in the axoplasm of the giant fiber. These findings, coupled with other evidence, have led us to conclude that the adaxonal glial cells synthesize a class of proteins which are transferred to the giant axon. Analysis of the kinetics of this phenomenon indicates that some proteins are transferred to the axon within minutes of their synthesis in the glial cells. One or more of the steps in the transfer process appear to involve Ca++, since replacement of extracellular Ca++ by either Mg++ or Co++ significantly reduces the appearance of labeled proteins in the axon. A substantial fraction of newly synthesized glial proteins, possibly as much as 40 percent, are transferred to the giant axon. These proteins are heterogeneous and range in size from 12,000 to greater than 200,000 daltons. Comparisons of the amount of amino acid incorporation in glia cells and neuron cell bodies raise the possibility that the adaxonal glial cells may provide an important source of axonal proteins which is supplemental to that provided by axonal transport from the cell body. These findings are discussed with reference to a possible trophic effect of glia on neurons and metabolic cooperation between adaxonal glia and the axon. 相似文献
43.
Formaldehyde run-off was an unintended impact of the anthrax decontamination procedure on the island of Gruinard. The death
of intertidal organisms was observed where formaldehyde reached the shore during 1986. The extent to which shores on Gruinard
have recovered was assessed with survey work in 2000. Recovery estimates were based on the hypothesis that the process of
recolonization is partly dependent on species’ dispersal capability. Underdevelopment of the assemblage of species lacking
planktonic dispersal stages (direct developers) is therefore evidence that the process of recolonization is ongoing, rather
than complete. A novel multivariate test showed that, when comparing quadrats from Gruinard and nearby mainland shores, assemblages
of direct developing molluscs were significantly more distinct than assemblages of molluscs with planktonic dispersal stages.
The average densities of species with direct development were generally lower on Gruinard than on mainland shores. While some
species with direct development have similar densities on Gruinard and on the surrounding shores, the recovery of the overall
assemblage was still incomplete after 14 years. In contrast, the harvested species, Littorina littorea, appeared to benefit from the absence of humans visiting Gruinard’s shores. Populations of L. littorea on Gruinard contained significantly higher proportions of large individuals. Depending on the dispersal capabilities of different
species, Gruinard is either still in recovery or acts as a reserve. 相似文献
44.
Genetic study reveals close link between Irish and Northern Spanish specimens of the protected Lusitanian slug Geomalacus maculosus
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Inga Reich Michael Gormally A. Louise Allcock Rory McDonnell José Castillejo Javier Iglesias Javier Quinteiro Cindy J. Smith 《Biological journal of the Linnean Society. Linnean Society of London》2015,116(1):156-168
The slug Geomalacus maculosus is a prominent member of the Lusitanian fauna. As its global distribution is restricted to western Ireland and northern Iberia, it is protected under EU legislation. Nothing is known about the genetic variability and population structure of this species, so, with a special view to shedding light on the origin of the Irish G. maculosus, tissue samples from 78 specimens were collected from 13 locations within Ireland and ten locations within Iberia and partial sequences of the mitochondrial 16S rRNA and cytochrome oxidase subunit 1 (COI) and from the nuclear internal transcribed spacer 1 region (ITS‐1) were compared. The genetic diversity of the Irish G. maculosus was found to be greatly reduced compared with the Iberian populations, with only one (16S rRNA) and two (COI) mitochondrial haplotypes identified respectively. No private Irish ITS‐1 haplotype was found. Based on the COI sequences, the Irish specimens clustered closest to Spanish specimens from Northern Asturias and Cantabria, and the bGMYC analysis identified five further Iberian clades that were highly genetically differentiated suggesting long‐term allopatric divergence. 相似文献
45.
Pauline?AaltenEmail author Inez?HGB?Ramakers Geert?Jan?Biessels Peter?Paul?de Deyn Huiberdina?L?Koek Marcel?GM?OldeRikkert Ania?M?Oleksik Edo?Richard Lieke?L?Smits John?C?van Swieten Laura?K?Teune Aad?van der Lugt Frederik?Barkhof Charlotte?E?Teunissen Nico?Rozendaal Frans?RJ?Verhey Wiesje?M?van der Flier 《BMC neurology》2014,14(1):254
46.
Morrow CC Picton BE Erpenbeck D Boury-Esnault N Maggs CA Allcock AL 《Molecular phylogenetics and evolution》2012,62(1):174-190
The current morphological classification of the Demospongiae G4 clade was tested using large subunit ribosomal RNA (LSU rRNA) sequences from 119 taxa. Fifty-three mitochondrial cytochrome oxidase 1 (CO1) barcoding sequences were also analysed to test whether the 28S phylogeny could be recovered using an independent gene. This is the largest and most comprehensive study of the Demospongiae G4 clade. The 28S and CO1 genetrees result in congruent clades but conflict with the current morphological classification. The results confirm the polyphyly of Halichondrida, Hadromerida, Dictyonellidae, Axinellidae and Poecilosclerida and show that several of the characters used in morphological classifications are homoplasious. Robust clades are clearly shown and a new hypothesis for relationships of taxa allocated to G4 is proposed. 相似文献
47.
Nukavarapu SP Kumbar SG Brown JL Krogman NR Weikel AL Hindenlang MD Nair LS Allcock HR Laurencin CT 《Biomacromolecules》2008,9(7):1818-1825
The nontoxic, neutral degradation products of amino acid ester polyphosphazenes make them ideal candidates for in vivo orthopedic applications. The quest for new osteocompatible materials for load bearing tissue engineering applications has led us to investigate mechanically competent amino acid ester substituted polyphosphazenes. In this study, we have synthesized three biodegradable polyphosphazenes substituted with side groups, namely, leucine, valine, and phenylalanine ethyl esters. Of these polymers, the phenylalanine ethyl ester substituted polyphosphazene showed the highest glass transition temperature (41.6 degrees C) and, hence, was chosen as a candidate material for forming composite microspheres with 100 nm sized hydroxyapatite (nHAp). The fabricated composite microspheres were sintered into a three-dimensional (3-D) porous scaffold by adopting a dynamic solvent sintering approach. The composite microsphere scaffolds showed compressive moduli of 46-81 MPa with mean pore diameters in the range of 86-145 microm. The 3-D polyphosphazene-nHAp composite microsphere scaffolds showed good osteoblast cell adhesion, proliferation, and alkaline phosphatase expression and are potential suitors for bone tissue engineering applications. 相似文献
48.
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