Interaction between constitutively expressed heat shock protein, Hsc 70, and cysteine string protein is important for cortical granule exocytosis in Xenopus oocytes

In many species, binding of sperm to the egg initiates cortical granule exocytosis, an event that contributes to a sustained block of polyspermy. Interestingly, cortical granule exocytosis can be elicited in immature Xenopus oocytes by the protein kinase C activator, phorbol-12-myristate-13-acetate. In this study, we investigated the role of cysteine string protein (csp) in phorbol-12-myristate-13-acetate-evoked cortical granule exocytosis. Prior work indicated that csp is associated with cortical granules of Xenopus oocytes. In oocytes exhibiting >20-fold overexpression of full-length Xenopus csp, cortical granule exocytosis was reduced by approximately 80%. However, csp overexpression did not affect constitutive exocytosis. Subcellular fractionation and confocal fluorescence microscopy revealed that little or none of the overexpressed csp was associated with cortical granules. This accumulation of csp at sites other than cortical granules suggested that mislocalized csp might sequester a protein that is important for regulated exocytosis. Because the NH2-terminal region of csp includes a J-domain, which interacts with constitutively expressed 70-kDa heat shock proteins (Hsc 70), we evaluated the effect of overexpressing the J-domain of csp. Although the native J-domain of csp inhibited cortical granule exocytosis, point mutations that interfere with J-domain binding to Hsc 70 eliminated this inhibition. These data indicate that csp interaction with Hsc 70 molecular chaperones is vital for regulated secretion in Xenopus oocytes.     

Rate of Change in Dormancy Level and Light Requirement in Weed Seeds During Stratification

The rate of change in dormancy level and light requirement,induced during stratification at 3.2 °C, was investigatedin seeds ofStellaria media, Cerastium fontanum, Veronica agrestisandTaraxacumofficinale.Two stratification environments, soil and wet filterpaper in petri-dishes, were used. On nine occasions during a6 week stratification period, germination was tested under threelight conditions at 3.5/18.5 °C: (1) darkness; (2) light;and (3) short-term light exposure followed by darkness. Priorto stratification, germination in all species was 89% in lightand 53% in darkness. Within 2 weeks of stratification, germinabilityinV. agrestisandS. mediaseeds decreased in all treatments. InC.fontanumandT. officinaleseeds, germinability also decreasedafter 2 weeks but only in the dark treatment, indicating inductionof a light requirement. After two more weeks of stratification,the induced dormancy inS. mediaseeds stratified in soil becameweaker and the light requirement inT. officinaleseeds was lost.Differences between the two stratification environments and/orinteractions between light conditions, stratification environmentsand time were found for all species. These results suggest that:(1) the dormancy level and the light requirement of seeds maychange dramatically over relatively short-time periods duringstratification; and (2) germinability depends on the stratificationenvironment experienced by the seeds. Predicting the dormancylevel or light requirement in a seed batch is difficult andrequires a thorough knowledge of the effect of the stratificationconditions used.Copyright 1997 Annals of Botany Company Burial; Cerastium fontanumBaumg.; chickweed; cold stratification; common mouse-ear; dandelion; dormancy; light requirement; seed; Stellaria media(L.) Vill.; speedwell; Taraxacum officinalegroup; Veronica agrestisL.; weed     

Patterns in benthic food webs: a role for omnivorous crayfish?

1. The biomass and species richness of macrophytes and invertebrates in artificial ponds at two sites in southern Sweden (twenty-one ponds at each site) were investigated. Alkalinity was high at one site (H ponds) and low at the other site (L ponds). The ponds chosen had different densities of signal crayfish (Pacifastacus leniusculus), with mean crayfish abundance (estimated by trapping and expressed as catch per unit effort) significantly higher in the L ponds (10.7) than in the H ponds (4.9). Macrophytes, invertebrates, the amount of periphyton on stones and the organic content of the sediment were determined in each pond. 2. Macrophyte biomass, cover and species richness declined with increasing crayfish density. Macrophyte species composition differed between ponds and was related to crayfish abundance. 3. The total biomass of invertebrates and the biomass of herbivorous/detritivorous invertebrates declined with increasing crayfish abundance, but the biomass of predatory invertebrates declined only in the L ponds. The relative biomass of Gastropoda and Odonata declined in ponds where crayfish were abundant. In ponds where crayfish were abundant the invertebrate fauna was dominated by sediment-dwelling taxa (Sialis (H and L ponds) and Chironomidae (H ponds)). 4. The number of invertebrate taxa in macrophytes declined with increasing crayfish abundance. The percentage of macrophyte-associated invertebrate taxa differed between ponds, but also between sites. The relative biomass of Gastropoda declined in H ponds where crayfish were abundant. In H ponds Trichoptera or Gammarus sp. and Heteroptera dominated where crayfish were abundant, whereas Odonata dominated in L ponds with abundant crayfish. 5. The organic content of the sediment decreased in ponds with high crayfish densities, while the amount of periphyton on stones was not related to crayfish density. 6. We conclude that the signal crayfish may play an important role as a keystone consumer in pond ecosystems, but lower trophic levels did not respond to changes in the abundance of the crayfish according to the trophic cascade model. Omnivorous crayfish may decouple the cascading effect.     

Common Cuckoo Cuculus canorus and host behaviour at Reed Warbler Acrocephalus scirpaceus nests

This study is based on continuous video recordings made at 53 Reed Warbler Acrocephalus scirpaceus nests each day during the laying period. Egg-laying by the Common Cuckoo Cuculus canorus was recorded in 14 (26.4%) of these nests. By analysing the activity of the host birds around and at the nest, we found that this is probably not the only cue used by the Common Cuckoo when locating suitable nests to parasitize. Furthermore, in most cases there was no significant difference between the length of time the host birds spent at the nest in the morning and afternoon, thus providing little support for the hypothesis that the Common Cuckoo lays in the afternoon because it is less likely to be seen by the nest owners then. Parasitized Reed Warblers rejected the Common Cuckoo egg more frequently when they observed the parasite at their nests. However, contrary to what should be expected, most Common Cuckoos laid their eggs in the presence of the host(s), and in general their egg-laying behaviour (for example duration of stay at the nest) was less secretive than described earlier. When partially depredating host clutches, Cuckoos showed the same behavioural pattern at parasitized and unparasitized nests, indicating that the latter may act as a potential reserve for egg-laying.     

Classification of the family Plectonemertidae (Nemertea): a phenetic comparison

A phenetic classification based on overall morphological similarity between the species in the family Plectonemertidae (genera Plectonemertes, Campbellonemertes, Potamonemertes, Leptonemertes, Katechonemertes, Argonemertes, Anliponemertes, and Acteonemertes) was undertaken and the result compared with a cladistic and an evolutionary classification. Similarity between species was computed by Gower's general coefficient of similarity and various techniques were used to find patterns in the similarity matrix: single-linkage, average-linkage, and complete-linkage clustering, together with principal coordinate analysis. Although the explicit aim of phenetics is not to estimate the phylogeny, the classification based on overall similarity still portrays phylogeny better than an intuitive assessment of morphological similarity, as judged by the cladistic analysis. The classification does not support the previously proposed hypothesis that the two freshwater genera Campbellonemertes and Potamonemertes have descended from a terrestrial ancestor.     

Observations on mixed cultures of nitrosomonas and heterotrophic soil bacteria

Plant and Soil - Naturally mixed cultures ofNitrosomonas and heterothrophic micro-organisms from soil have been examined. The autotrophicNitrosomonas as well as heterotrophic bacteria would grow...     

Status,trends and drivers of kelp forests in Europe: an expert assessment

A comprehensive expert consultation was conducted in order to assess the status, trends and the most important drivers of change in the abundance and geographical distribution of kelp forests in European waters. This consultation included an on-line questionnaire, results from a workshop and data provided by a selected group of experts working on kelp forest mapping and eco-evolutionary research. Differences in status and trends according to geographical areas, species identity and small-scale variations within the same habitat where shown by assembling and mapping kelp distribution and trend data. Significant data gaps for some geographical regions, like the Mediterranean and the southern Iberian Peninsula, were also identified. The data used for this study confirmed a general trend with decreasing abundance of some native kelp species at their southern distributional range limits and increasing abundance in other parts of their distribution (Saccharina latissima and Saccorhiza polyschides). The expansion of the introduced species Undaria pinnatifida was also registered. Drivers of observed changes in kelp forests distribution and abundance were assessed using experts’ opinions. Multiple possible drivers were identified, including global warming, sea urchin grazing, harvesting, pollution and fishing pressure, and their impact varied between geographical areas. Overall, the results highlight major threats for these ecosystems but also opportunities for conservation. Major requirements to ensure adequate protection of coastal kelp ecosystems along European coastlines are discussed, based on the local to regional gaps detected in the study.     

Microtubules and actin filaments are not critically involved in the biogenesis of epithelial cell surface polarity

We have studied the role of microtubules and actin filaments in the biogenesis of epithelial cell surface polarity, using influenza hemagglutinin and vesicular stomatitis G protein as model apical and basolateral proteins in infected Madin-Darby canine kidney cells. Addition of colchicine or nocodazole to confluent monolayers at concentrations sufficient to completely disassemble microtubules did not affect the asymmetric budding of influenza or vesicular stomatitis virus and only slightly reduced the typical asymmetric surface distribution of their envelope proteins, despite extensive cytoplasmic redistribution of the Golgi apparatus. Alteration of microtubular function by taxol or dissociation of actin filaments by cytochalasin D also failed to have a significant effect. Furthermore, neither colchicine nor cytochalasin D pretreatment blocked the ability of subconfluent Madin-Darby canine kidney cells to sustain polarized budding of influenza virus a few hours after attachment to the substrate. Our results indicate that domain-specific microtubule or actin filament "tracks" are not responsible for the vectorial delivery of apically or basolaterally directed transport vesicles. In conjunction with currently available evidence, they are compatible with a model in which receptors in the cytoplasmic aspect of apical or basolateral regions provide vectoriality to the transport of vesicles carrying plasma membrane proteins to their final surface localization.     

Enhanced stability of microtubules enriched in detyrosinated tubulin is not a direct function of detyrosination level

Interphase cultured monkey kidney (TC-7) cells contain distinct subsets of cellular microtubules (MTs) enriched in posttranslationally detyrosinated (Glu) or tyrosinated (Tyr) alpha tubulin (Gundersen, G. G., M. H. Kalnoski, and J. C. Bulinski. 1984. Cell. 38:779-789). To determine the relative stability of these subsets of MTs, we subjected TC-7 cells to treatments that slowly depolymerized MTs. We found Glu MTs to be more resistant than Tyr MTs to depolymerization by nocodazole in living cells, and to depolymerization by dilution in detergent-permeabilized cell models. However, in cold-treated cells, Glu and Tyr MTs did not differ significantly in their stability. Digestion of permeabilized cell models with pancreatic carboxypeptidase A, to generate Glu MTs from endogenous Tyr MTs, did not significantly alter the resistance of the endogenous Tyr MTs toward dilution-induced depolymerization. Furthermore, in human fibroblasts that contained no distinct Glu MTs, we observed a population of nocodazole-resistant MTs. These data suggest that Glu MTs possess enhanced stability against end-mediated depolymerization, yet detyrosination alone appears to be insufficient to confer this enhanced stability.