Dynamic rearrangement of the filamentous actin network occurs during zoosporogenesis and encystment in the oomycete phytophthora cinnamomi

The organization of filamentous actin (F-actin) in living cells of the oomycete Phytophthora cinnamomi was determined during zoosporogenesis and zoospore encystment by microinjecting sporangia with fluorescently labeled phalloidin and observing resultant fluorescence by confocal microscopy. In multinucleate sporangia prior to the induction of cleavage, phalloidin labeling took the form of plaques which occurred mainly in the periphery of the sporangia. After induction of cleavage, phalloidin labeling showed that the plaques disappeared and that F-actin began to accumulate along the developing cleavage planes and around nuclei and water expulsion vacuoles. F-actin labeling was also observed near the plasma membrane in zoospores and young cysts but reverted to the plaque form in older cysts. Localization of F-actin close to the developing cleavage planes is consistent with the idea that actin microfilaments function in the positioning and expansion of the cleavage membranes. Observations of plaques of actin in living sporangia provide evidence that plaques are not aldehyde-induced fixation artifacts. Copyright 1998 Academic Press.     

HIV-particles in spermatozoa of patients with AIDS and their transfer into the oocyte

By immunocytochemistry and in situ hybridization at the electron microscopy level, and by the PCR technique, we have shown that HIV-1 binds and enters normal sperm; that viral particles, their antigens, and nucleic acid are present in sperm from HIV-1 infected men; and that such sperm can transfer HIV-1 like particles to normal human oocytes. We also present evidence that a galactosylceramide-like compound is present on the sperm membrane and could function as an alternative receptor for HIV.     

Unusual pattern of bacterial ice nucleation gene evolution

Bacterial ice nucleation activity (INA+ phenotype) can be traced to the product of a single gene, ina. A remarkably sparse distribution of this phenotype within three bacterial genera indicates that the ina gene may have followed an unusual evolutionary path. Southern blot analyses, coupled with assays for ice-nucleating ability, revealed that within four bacterial species an ina gene is present in some strains but absent from others. Results of hybridization experiments using DNA fragments that flank the ina gene suggested that the genotypic dimorphism of ina may be anomalous. A phylogenetic analysis of 16S ribosomal RNA gene sequences from a total of 14 ina+ and ina- bacterial strains indicated that the ina+ bacteria are not monophyletic but instead phylogenetically interspersed among ina- bacteria. The relationships of ina+ bacteria inferred from ina sequence did not coincide with those inferred from the 16S data. These results suggest the possibility of horizontal transfer in the evolution of bacterial ina genes.      

Relationship between the golgi apparatus, gerl, and secretory granules in acinar cells of the rat exorbital lacrimal gland

The method of secretory granuleformation in the acinar cells of the rat exorbital lacrimal gland was studied by electron microscope morphological and cytochemical techniques. Immature secretory granules at the inner face of the Golgi apparatus were frequently attached to a narrow cisternal structure similar to GERL as described in neurons by Novikoff et al. (Novikoff, P. M., A. B. Novikoff, N. Quintana, and J.-J. Hauw. 1971. J. Cell Bio. 50:859-886). In the lacrimal gland. GERL was located adjacent to the inner Golgi saccule, or separated from it by a variable distance. Portions of GERL were often closely paralleled by modified cisternae of rough endoplasmic reticulum (RER), which lacked ribosomes on the surface adjacent to GERL. Diaminobenzidine reaction product of the secretory enzyme peroxidase was localized in the cisternae of the nuclear envelope, RER, peripheral Golgi vesicles, Golgi saccules, and immature and mature secretory granules. GERL was usually free of peroxidase reaction product or contained only a small amount. Thiamine pyrophosphatase reaction product was present in two to four inner Golgi saccules; occasionally, the innermost saccule was dilated and fenestrated, and contained less reaction product than the next adjacent saccule. Acid phosphatase (AcPase) reaction product was present in GERL, immature granules, and, rarely, in the innermost saccule, but not in the rest of the Golgi saccules. Thick sections of AcPase preparations viewed at 100 kV revealed that GERL consisted of cisternal, and fenestrated or tublular portions. The immature granules were attached to GERL by multiple connections to the tublular portions. These results suggest that, in the rat exorbital lacrimal gland, the Golgi saccules participate in the transport of secretory proteins, and that GERL is involved in the formation of secretory granules.     

Inferring Mycobacterium bovis transmission between cattle and badgers using isolates from the Randomised Badger Culling Trial

Mycobacterium bovis (M. bovis) is a causative agent of bovine tuberculosis, a significant source of morbidity and mortality in the global cattle industry. The Randomised Badger Culling Trial was a field experiment carried out between 1998 and 2005 in the South West of England. As part of this trial, M. bovis isolates were collected from contemporaneous and overlapping populations of badgers and cattle within ten defined trial areas. We combined whole genome sequences from 1,442 isolates with location and cattle movement data, identifying transmission clusters and inferred rates and routes of transmission of M. bovis. Most trial areas contained a single transmission cluster that had been established shortly before sampling, often contemporaneous with the expansion of bovine tuberculosis in the 1980s. The estimated rate of transmission from badger to cattle was approximately two times higher than from cattle to badger, and the rate of within-species transmission considerably exceeded these for both species. We identified long distance transmission events linked to cattle movement, recurrence of herd breakdown by infection within the same transmission clusters and superspreader events driven by cattle but not badgers. Overall, our data suggests that the transmission clusters in different parts of South West England that are still evident today were established by long-distance seeding events involving cattle movement, not by recrudescence from a long-established wildlife reservoir. Clusters are maintained primarily by within-species transmission, with less frequent spill-over both from badger to cattle and cattle to badger.     

Recruitment,Growth and Mortality of an Antarctic Hexactinellid Sponge,Anoxycalyx joubini

Polar ecosystems are sensitive to climate forcing, and we often lack baselines to evaluate changes. Here we report a nearly 50-year study in which a sudden shift in the population dynamics of an ecologically important, structure-forming hexactinellid sponge, Anoxycalyx joubini was observed. This is the largest Antarctic sponge, with individuals growing over two meters tall. In order to investigate life history characteristics of Antarctic marine invertebrates, artificial substrata were deployed at a number of sites in the southern portion of the Ross Sea between 1967 and 1975. Over a 22-year period, no growth or settlement was recorded for A. joubini on these substrata; however, in 2004 and 2010, A. joubini was observed to have settled and grown to large sizes on some but not all artificial substrata. This single settlement and growth event correlates with a region-wide shift in phytoplankton productivity driven by the calving of a massive iceberg. We also report almost complete mortality of large sponges followed over 40 years. Given our warming global climate, similar system-wide changes are expected in the future.     

Progesterone induces nano‐scale molecular modifications on endometrial epithelial cell surfaces

Background information. The endometrial epithelial cell membrane is a key interface in female reproductive biology. Steroid hormones play a predominant role in cyclic changes which occur at this interface during the female menstrual cycle. Specific changes in the morphology of the endometrial epithelial cell surface become apparent with the epithelial transition that drives the switch from a non‐receptive to receptive surface due to the action of progesterone on an oestrogen primed tissue. AFM (atomic force microscopy) allows the high‐resolution characterization of the endometrial epithelial cell surface. Its contact probe mechanism enables a unique imaging method that requires little sample preparation, yielding topographical and morphological characterization. By stiffening the cell membrane, low concentrations of fixatives allow the surface detail of the cell to be resolved while preserving fine ultra‐structural details for analysis. Results. In the present study we use high resolution AFM analysis of endometrial epithelial cells to monitor the effect of progesterone on the nanoscale structure of the endometrial cell surface. High‐resolution imaging reveals similar topographical nanoscale changes in both the Hec‐1‐A and Ishikawa model cell lines. Hec‐1‐B cells, used in the present study as a progesterone receptor negative control, however, exhibit a flattened cell surface morphology following progesterone treatment. Changes in average cell height and surface convolution correlate with increased surface roughness measurements, demonstrating alterations in molecular structure on the cell surface due to hormonal stimulation. Conclusions. Progesterone treatment induces changes to the cell surface as a result of nanoscale molecular modifications in response to external hormonal treatments. AFM provides the basis for the identification, visualization and quantification of these cell surface nanoscale changes. Together these findings demonstrate the utility of AFM for use in reproductive science and cancer biology where it could be applied in both in vitro analysis of protein structure—function relationships and clinical diagnosis.     

Oral immunization of mice with a glycoconjugate vaccine containing the O157 antigen of Escherichia coli O157:H7 admixed with cholera toxin fails to elicit protection against subsequent colonization by the pathogen

It has been postulated that a humoral immune response directed against the O157 antigen of Escherichia coli O157:H7, and expressed in the intestine, might afford protection from colonization and consequent infection by this enteric pathogen. The present study was conducted to determine whether such an immune response can be experimentally generated in mice. To this end, mice were orally immunized with a glycoconjugate vaccine consisting of horse serum albumin and the O157 polysaccharide admixed with the mucosal adjuvant, cholera toxin. Mice consistently developed robust local and systemic immune responses to the cholera toxin adjuvant, but were far from uniformly reactive to the test vaccine. Moreover, vaccinated mice were as susceptible to transient intestinal colonization following challenge with an isolate of E. coli O157:H7 as unvaccinated control mice. These results indicate that this vaccination approach is unlikely to be straightforward in target bovine or human hosts.     

Functional genomics of Helicobacter pylori: identification of a beta-1,4 galactosyltransferase and generation of mutants with altered lipopolysaccharide

A previously annotated open reading frame (ORF) (HP0826) from Helicobacter pylori was cloned and expressed in Escherichia coli cells and determined to be a beta-1,4-galactosyltransferase that used GlcNAc as an acceptor. Mutational analysis in H. pylori strains demonstrated that this enzyme plays a key role in the biosynthesis of the type 2 N-acetyl-lactosamine (LacNAc) polysaccharide O-chain backbone, by catalysing the addition of Gal to GlcNAc. To examine the potential role of this O-chain structure in bacterial colonization of the host stomach, the mutation was introduced into H. pylori strain SS1 which is known to be capable of colonizing the gastric mucosa of mice. Compared with the parental strain, mutated SS1 was less efficient at colonizing the murine stomach.