Human microbiome: a genetic bazaar for microbes?

A recent study suggests that lateral gene transfer has been particularly intense among human-associated microbes. What can this tell us about our relationship with our internal microbial world?     

Benefits,costs and reactivity of inducible defences: an experimental test with rotifers

1. A key aspect of the ecology and evolution of adaptive prey responses to predator risk is the timing by which the former develop a defensive trait in response to inducing signals released by the latter. This property, called reactivity, has been shown to affect population stability and persistence. 2. Theoretically, the minimal predator density required by prey to exhibit induced defences is expected to increase with the effectiveness of the defence and decrease with its cost. Likewise, the time required for the prey population to exhibit an induced defence is expected to increase together with cost. 3. The freshwater rotifers Brachionus calyciflorus and B. havanaensis and their predator Asplanchna brightwelli were used to test the hypothesis that prey species exhibiting defences that offer a larger fitness benefit and lower fitness cost are more reactive to predator signals, in terms of requiring shorter exposure time and lower signal concentration to trigger a morphological defence reaction. 4. Our results showed that both prey species exhibited costly and effective defences after induction by predator infochemicals. Faster reactions were observed at higher levels of predator cues. Nevertheless, the observed relationship between reactivity and benefit/cost of defences did not agree with our expectations. 5. To our knowledge, this is the first study in which the timing of induction of morphological defences is experimentally assessed over a gradient of risk signals. We propose new research directions to disentangle the mechanisms and project the consequences of prey decisions at the morphological level.     

Progesterone and gravidity differentially regulate expression of extracellular matrix components in the pregnant rat myometrium

Myometrial growth and remodeling during pregnancy depends on increased synthesis of interstitial matrix proteins. We hypothesize that the presence of mechanical tension in a specific hormonal environment regulates the expression of extracellular matrix (ECM) components in the uterus. Myometrial tissue was collected from pregnant rats on Gestational Days 0, 12, 15, 17, 19, 21, 22, 23 (labor), and 1 day postpartum and ECM expression was analyzed by Northern blotting. Expression of fibronectin, laminin beta2, and collagen IV mRNA was low during early gestation but increased dramatically on Day 23 during labor. Expression of fibrillar collagens (type I and III) peaked Day 19 and decreased near term. In contrast, elastin mRNA remained elevated from midgestation onward. Injection of progesterone (P4) on Days 20-23 (to maintain elevated plasma P4 levels) delayed the onset of labor, caused dramatic reductions in the levels of fibronectin and laminin mRNA, and prevented the fall of collagen III mRNA levels on Day 23. Treatment of pregnant rats with the progesterone receptor antagonist RU486 on Day 19 induced preterm labor on Day 20 and a premature increase in mRNA levels of collagen IV, fibronectin, and laminin. Analysis of the uterine tissue from unilaterally pregnant rats revealed that most of the changes in ECM gene expression occurred specifically in the gravid horn. Our results show a decrease in expression of fibrillar collagens and a coordinated temporal increase in expression of components of the basement membrane near term associated with decreased P4 and increased mechanical tension. These ECM changes contribute to myometrial growth and remodeling during late pregnancy and the preparation for the synchronized contractions of labor.     

Phylogenetic relationships and taxonomic position of Chlorella -like isolates from low pH environments (pH < 3.0)

Background  

Little is known about phytoplankton communities inhabiting low pH environments such as volcanic and geothermal sites or acidic waters. Only specialised organisms are able to tolerate such extreme conditions. There is, thus, low species diversity. We have characterised the previously isolated acid tolerant Chlorella -like microalgae Viridiella fridericiana and Chlorella protothecoides var. acidicola by microscopical and biomolecular methods in order to assess their phylogenetic relationships.     

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.     

Calcification of Cartilage from the Lamprey Petromyzon marinus (L.) in vitro

Abstract Adult and larval lamprey cartilage, normally unmineralized, was cultured in a medium meta-stable for hydroxyapatite for periods of up to 12 days at 20, 30 or 37°C. Histochemical analysis revealed a temperature-dependent increase over time in calcium phosphate incorporation into the extracellular matrix (ECM) of adult cartilage concomitant with the incorporation of calcium as detected by gravimetric and radioisotopic methods. Ultrastructural analysis revealed the presence of ECM dense bodies (40 nm average) containing crystalline material which increased in number with increased mineral incorporation but were absent from control cartilage. Additionally, electron-dense particles (15–20 nm) found in close association with the ECM fibrils in some regions of mineralized cartilage may represent sites of amorphous calcium phosphate. Larval cartilage incorporated much less calcium, less uniformly over time than did adult cartilage. Histochemical and ultrastructural analysis revealed that calcium had accumulated in the chondrocytes instead of the ECM and this proved detrimental, leading to the death of the cells. The discovery that adult lamprey cartilage calcifies in vitro under appropriate conditions, suggests that petromyzonids, or their direct agnathan ancestors, may have possessed mineralized skeletons and that this ability is ‘repressed’ in extant lampreys owing primarily to the environment they inhabit.     

Three patterns of distribution characterize the organization of endothelial microfilaments at aortic flow dividers

Since actin microfilaments are essential in the maintenance of endothelial integrity and in the repair of injured endothelium, we have carried out a detailed study of the distribution of microfilaments in the immediate vicinity of aortic branches. Branches are of major interest because there is a predilection for atherosclerotic lesions near branch ostia. We made an extensive, systematic examination of branches of the aorta and iliac arteries using in situ staining of perfusion-fixed arteries. Microfilaments were localized using rhodamine phalloidin. Three patterns of staining were observed. Some endothelial cells showed prominent central stress fibers. Others had few central stress fibers but prominent peripheral fibers. Still others showed an intermediate pattern with some central and some peripheral fibers present. At small branch sites, the lip of the divider was more blunt, and there were more cells with peripheral actin. At large branches, cells with peripheral actin were confined mainly to the lip, while there were many more cells with prominent central fibers. We also found that major differences can occur over very small distances, so adjacent cells may have strikingly different patterns of microfilament distribution. These patterns appear to reflect the geometry of the flow divider and local variations in hemodynamic shear stress. The differences in microfilament distribution may reflect differences in endothelial functions which are essential in maintaining endothelial integrity.     

Stable,position-related responses to retinoic acid by chick limb-bud mesenchymal cells in serum-free cultures

Summary Retinoic acid (RA) has dramatic effects on limb-skeletal patterning in vivo and may well play a pivotal role in normal limb morphogenesis. RA&#x2019;s effects on the expression of pattern-related genes in the developing limb are probably mediated by cytoplasmic RA-binding proteins and nuclear RA-receptors. Little is known, however, about how RA modifies specific cellular behaviors required for skeletal morphogenesis. Earlier studies supported a role for regional differences in RA concentration in generating the region-specific cell behaviors that lead to pattern formation. The present study explores the possibility that position-related, cell-autonomous differences in the way limb mesenchymal cells respond to RA might have a role in generating pattern-related cell behavior. Mesenchymal cells from different proximodistal regions of stage 21&#x2013;22 and 23&#x2013;24 chick wing-buds were grown in chemically defined medium and exposed to 5 or 50 ng/ml of RA for 4 days in high-density microtiter cultures. The effects of RA on chondrogenesis in these cultures clearly differed depending on the limb region from which the cells were isolated. Regional differences in RA&#x2019;s effects on growth over 4 days in these cultures were less striking. The region-dependent responses of these cells to RA proved relatively stable in culture despite ongoing cytodifferentiation. This serum-free culture model will be useful in exploring the mechanisms underlying the region-dependent responsiveness of these cells to RA.