The cercarial glycocalyx of Schistosoma mansoni

Cercariae, the freshwater stage of Schistosoma mansoni infectious to man, are covered by a single unit membrane and an immunogenic glycocalyx. When cercariae penetrate the host skin, they transform to schistosomula by shedding tails, secreting mucous and enzymes, and forming microvilli over their surface. Here the loss of the glycocalyx from cercariae transforming in vitro was studied morphologically and biochemically. By scanning electron microscopy, the glycocalyx was a dense mesh composed of 15-30 nm fibrils that obscured spines on the cercarial surface. The glycocalyx was absent on organisms fixed without osmium and was partially lost when parasites aggregated in their own secretions before fixation. By transmission electron microscopy, a 1-2 microns thick mesh of 8-15-nm fibrils was seen on parasites incubated with anti-schistosomal antibodies or fixed in aldehydes containing tannic acid or ruthenium red. Cercariae transformed to schistosomula when tails were removed mechanically and parasites were incubated in saline. Within 5 min of transformation, organisms synchronously formed microvilli which elongated to 3-5 microns by 20 min and then were shed. However, considerable fibrillar material remained adherent to the double unit membrane surface of schistosomula. For biochemical labeling, parasites were treated with eserine sulfate, which blocked cercarial swimming, secretion, infectivity, and transformation to schistosomula. Material labeled by periodate oxidation and NaB3H4 was on the surface as shown by autoradiography and had an apparent molecular weight of greater than 10(6) by chromatography. Periodate-NaB3H4 glycocalyx had an isoelectric point of 5.0 +/- 0.4 and was precipitable with anti-schistosomal antibodies. More than 60% of the radiolabeled glycocalyx was released into the medium by transforming parasites in 3 h and was recovered as high molecular weight material. Parasites labeled with periodate and fluorescein-thiosemicarbazide and then transformed had a corona of fluorescence containing microvilli, much of which was shed onto the slide. Material on cercariae labeled by lodogen-catalyzed iodination was also of high molecular weight and was antigenic. In conclusion, the cercarial glycocalyx appears to be composed of acidic high molecular weight fibrils which are antigenic and incompletely cleared during transformation.     

The effect of praziquantel on the ultrastructure of Schistosoma margrebowiei

The effect of various concentrations of praziquantel at different time intervals post-treatment on the ultrastructure of Schistosoma margrebowiei using scanning and transmission electron microscopy has been examined. The major changes involved blebbing of the entire surface tegument of both sexes (although more marked in males) together with vacuolation of the basal membrane accompanied by the development of membraneous whorls. These effects were progressively more marked with increased concentration and time of exposure resulting in severe erosion of the tubercles and collapse of the sensory organelles. Exposure of the underlying tegumental tissue resulted and paralysis and contraction of the suckers and neck region was apparent. Disruption of the subtegumental musculature and the appearance of vacuolation and membraneous whorl formation were seen. The gastrodermis was similarly affected and the S4 cells of the vitelline gland showed protein disruption of the vitelline droplets. Host cells were seen adhering to the surface of the worms following drug treatment and the synergism between PZQ and the action of the hosts immune system has been discussed.     

The semidian rhythm in flowering response of Pharbitis nil in relation to dark period time measurement and to a circadian rhythm

When seedlings of Pharbitis nil Choisy, cv. Violet, are exposed to a single inductive dark period at 27°C, brief interruptions with red light (R) can be promotive after 2–3 h of darkness but increasingly inhibitory to flowering up to the 8–9th h of darkness. This rhythmic response to R interruptions can be advanced in phase by > 1 h when the preceding light period is interrupted with far-red (FR) 2 h before darkness (FR -2 h) or with FR – 15 h, whereas FR –8 h or FR–22 h retard the rhythm. These shifts in the R interruption rhythm are paralleled by equal shifts in the length of the dark period required for flowering. Brief FR interruptions of darkness displayed a similar rhythm which was also advanced by FR –2 h and retarded by FR –8 h. We conclude therefore that the semidian rhythm in the light, which we have previously described, continues through at least the first 12 h of darkness, is manifested in the R interruption rhythm, and determines the critical night length. A circadian rhythm with a marked effect on flowering was also identified, but several lines of evidence suggest that the circadian and semidian rhythms have independent additive effects on flowering and do not appear to show phase interaction.     

Protein degradation in lemna with particular reference to ribulose bisphosphate carboxylase: I. The effect of light and dark

Ribulose bisphosphate carboxylase from Lemna minor resembles the structure reported for the enzyme from other plants. When grown in the light, the enzyme appears to undergo little or no degradation, as measured by a double-isotope method. This situation is similar to that reported for wheat and barley, but is unlike that reported for maize, where the enzyme degrades at the same rate as total protein. Prolonged periods of darkness usually induce leaf senescence, characterized by the rapid degradation of chlorophyll and protein, with ribulose bisphosphate carboxylase undergoing preferential degradation. In L. minor there is selective protein degradation in the dark, but chlorophyll and ribulose bisphosphate carboxylase are stable when fronds are kept in the darkness for up to 8 days. It appears that Lemna is not programmed to senesce, or at least that darkness does not induce senescence in Lemna. Although there is no evidence for in vivo degradation or modification of ribulose bisphosphate carboxylase during prolonged periods of darkness, extracts from fronds which have been kept in the dark for periods in excess of 24 hours convert ribulose bisphosphate carboxylase to a more acidic form. The properties of the dark-induced system which acts on ribulose bisphosphate carboxylase, suggest that it may be a mixed function oxidase. The proposition that the selectivity of protein degradation is genetically determined, so that the rate at which a protein is degraded is determined by its charge or size, was tested for fronds grown in the light or maintained in the dark. There was no significant correlation between protein degradation and either charge or size, in light or dark.     

The daily rhythm of mice

The house mouse Mus musculus represents a valuable tool for the analysis and the understanding of the mammalian circadian oscillator. Forward and reverse genetics allowed the identification of clock components and the verification of their function within the circadian clockwork. In many cases unforeseen links were discovered between a particular circadian regulatory protein and various diseases or syndromes. Thus, this model system is not only perfectly suited to pinpoint the components of the mammalian circadian clock, but also to unravel metabolic, physiological, and pathological processes linked to the circadian timing system.     

Genetic variability of Schistosoma bovis cercarial production according to miracidial dose

Cercarial production related to miracidial dose variation with Schistosoma bovis strains from Sudan and Spain in Bulinus truncatus from Tunisia was studied. Results showed that an increase in the miracidial dose proposed to the host-mollusc (1 and 5 miracidia) gave rise to a decrease in cercarial productivity of Sudanese S. bovis and to an increase for Spanish S. bovis. It is concluded that this response difference to the miracidial dose variation depends on genetic characters peculiar to the parasite strain and represents a new aspect of genetic variability of schistosome populations.     

The cercarial output from three Nigerian bulinids infected with two strains of Schistosoma haematobium

The daily cercarial output of two Nigerian strains of Schistosoma haematobium in sympatric Bulinus truncatus, B. globosus and B. senegalensis was measured at weekly intervals from the start of emission to the snails' death. In all cases cercariae were released throughout the life of the host, with no cases of "self cure". Patterns of output through the course of infections in B. truncatus and B. senegalensis were similar to those reported for S. haematobium by other workers, with daily production of cercariae rising to a peak within a few weeks of the onset of shedding, then declining until the host's death. In the longer lived B. globosus production was significantly higher, but declined to very low levels after the initial peak; in some individuals cercarial output remained very low, while others showed a second period of high cercarial emission. The relative compatibility of each host-parasite combination is discussed.     

The arthropod fauna of Quebec vineyards with particular reference to phytophagous arthropods

A 3-yr study using different sampling and trapping techniques showed that the arthropod pest fauna in two commercial vineyards in southwestern Quebec was qualitatively and quantitatively different than that of Ontario, Canada, and New York state. We hypothesize that a colder winter climate in addition to the agronomic activity of earthing up around the vines in autumn to protect the roots from freezing in winter contributed to low numbers of pests, such as the grape berry moth, Endopiza viteana Clemens (Lepidoptera, Tortricidae). Once in 3 yr, the density of this pest approached, in one of the vineyards, the action threshold recommended for New York. Therefore, it should be monitored on an annual basis. Another phytophagous arthropod that has the potential to cause sporadic economic damage is the potato leafhopper, Empoasca fabae (Harris). The Asiatic garden beetle, Maladera (= Autoserica) castanea (Arrow), was reported for the first time in Canada. The tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), was also captured by sampling. However, its status as a pest has yet to be clarified.     

The role of prostaglandins in cercarial (Schistosoma mansoni) response to free fatty acids

In examining the structure-activity relationship of a diverse group of chemicals reported to prevent cercarial penetration after topical application, we noticed a moiety that was common to free fatty acids and prostaglandins. Because unsaturated fatty acids have been reported to stimulate cercarial penetration, we hypothesized that cercarial stimulation by skin and fatty acids may invoke prostaglandin mechanisms in cercariae, skin, or both. Thus we compared the stimulation of cercariae by a series of essential and nonessential fatty acids and demonstrated an inhibition of this response by ibuprofen and aspirin, known cyclo-oxygenase inhibitors, and by 13-azaprostanoic acid, a potent antagonist of the thromboxane/endoperoxide receptor. These data led us to postulate a major role for prostaglandins in the cercarial penetration response.