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PubMed1999

Cloning of a beta integrin subunit cDNA from an embryonic cell line derived from the freshwater mollusc, Biomphalaria glabrata.

A cDNA encoding an integrin subunit was cloned and structurally characterized from an embryonic cell line derived from Biomphalaria glabrata, snail intermediate host of the human blood fluke Schistosoma mansoni. Cells of the B. glabrata embryonic (Bge) snail cell line were initially tested for their sensitivity to the integrin-specific tetrapeptide inhibitor Arg-Gly-Asp-Ser (RGDS). Washed Bge cells when exposed to 0.5 to 2.0mM of RGDS were significantly inhibited in their ability to spread on a glass substrate. Spreading inhibition was specific, since a control peptide Arg-Gly-Glu-Ser (RGES) did not have the same effect. RT-PCR was performed using previously reported degenerate oligonucleotide primers to the ligand binding domain (LBD) of known beta integrin subunits and Bge cDNA. A 137 bp fragment was amplified, TA-cloned, sequenced, and the na and deduced aa sequences were compared with other beta integrins. Databank analysis showed that the 137 bp product shared >/=55.6% aa similarity to other beta integrin LBDs. Southern and northern blot analyses using the 137 bp sequence as a probe revealed binding to Bge genomic DNA restriction fragments and to an approximately 8 kb poly-(A)+RNA transcript, respectively. An exact 5' primer synthesized to the 137 bp product and an oligo-d(T) primer then were used to amplify from Bge cDNA, a partial beta integrin sequence of 2285 bp that contained a 1971 bp ORF. The remaining upstream coding region was obtained using 5' RACE methods. The complete ORF, consisting of 2364 bp, encoded a 788 aa sequence with shared similarity to other known beta integrins (44.6-61.5%). Sequence and structural comparisons, which include a characteristic LBD, a series of three homologous cysteine-rich repeats, membrane proximal sequence (LLTFIHD), cytoplasmic NPXY motifs, and predicted domain lengths of the molluscan protein, clearly identifies it as an integrin homologue. This report represents the first cloning of a cDNA putatively encoding an integrin subunit from molluscan cells, and establishes the Bge cell line as a model for studying cellular adhesion in molluscs at the molecular level.

Amino Acid Sequence↗
PubMed2000

Molluscicidal activity of some Saudi Arabian euphorbiales against the snail Biomphalaria pfeifferi.

The comparative susceptibility of the snail vector of intestinal schistosomiasis, Biomphalaria pfeifferi to the action of extracts from Saudi Arabian Euphorbiales has been determined. Methanol and chloroform extracts of the plants tested (Jatropha glauca, Euphorbia helioscopia and Euphorbia schimperiana) were the most promising from the molluscicidal point of view with LD(50) values in the range 10-100 ppm.

Animals↗
PubMed2003

Establishment of the dominant lethal test in the freshwater mollusk Biomphalaria glabrata (Say, 1818).

Mutagens in the environment may represent a long-term risk for ecosystems. The reproductive potential of populations can be affected by alterations in the fecundity and offspring viability caused by germ cell mutations. Despite the ecological relevance of these effects, there are few studies on germ cell mutagenicity in natural populations. Biomphalaria glabrata was chosen for this study because of the scarcity of data on freshwater invertebrates and the ecological importance of this group. The aim of this study was to establish a germ cell mutagenicity test in B. glabrata by using a similar approach to that used in the dominant lethal test in rodents. Mitomycin C was used as a direct mutagen and cyclophosphamide as a mutagen that requires metabolic activation. Wild-type snails were exposed for 10 days to three concentrations of each agent and crossed with non-exposed albino snails at the end of the treatment. The total frequencies of malformations were analyzed in the offspring of wild-type snails; among the offspring of albino snails, only the heterozygous wild-type embryos were analyzed for malformations. Both agents induced germ cell mutations. The analysis of the offspring of the wild-type snails showed an effect of the exposure up to approximately 5 days after the end of the treatment with cyclophosphamide; the effect of mitomycin C was observed until 45 days after the end of the exposure. There was an increase in the frequencies of malformations in the wild-type offspring of the non-exposed albino snails crossed with the wild-type snails exposed to both agents. The dominant lethal test in B. glabrata proposed in this work is easy to perform, efficient, specific and sensitive in the evaluation of germ cell mutations induced by reference mutagens. The possibility of expanding its use to environmental biomonitoring studies seems very promising and worth trying.

Animals↗
PubMed2003

The major soluble 19.6 kDa protein of the organic shell matrix of the freshwater snail Biomphalaria glabrata is an N-glycosylated dermatopontin.

The major Biomphalaria glabrata shell matrix protein of 19.6 kDa was isolated by preparative electrophoresis and sequenced. The sequence of 148 amino acids showed 32% sequence identity to mammalian dermatopontin sequences and 34-37% identity to two invertebrate dermatopontins described previously. A unique feature of the shell matrix dermatopontin was the presence of a single N-glycosylation consensus sequence, the asparagine of which was completely modified with a pentasaccharide. Sequence analysis of this short N-glycan by mass spectrometry and carbohydrate composition analysis indicated that it was the ubiquitous N-glycan core oligosaccharide with the exception that the terminal mannoses were 3-O-methylated. Dermatopontin is widespread in mammalian extracellular matrices, including the matrix of biominerals such as bone and teeth. Its occurrence in an invertebrate biomineral indicates that such phylogenetically distant biomineral-forming systems as vertebrate bone and mollusk shell share components which have undergone surprisingly few changes during a long evolution.

Amino Acid Sequence↗
PubMed2003

The influence of demography, population structure and selection on molecular diversity in the selfing freshwater snail Biomphalaria pfeifferi.

Several forces may affect the distribution of genetic diversity in natural populations when compared to what is expected in a random-mating, constant size population of neutral genes. One solution for unravelling their respective influence is to study several genes at once in order to better reflect the true genealogy. Here we reconstruct the evolutionary history of the freshwater snail Biomphalaria pfeifferi over its entire distribution, using eight African populations, and three congeneric species as outgroups. A phylogenetic analysis was conducted using amplified fragment length polymorphism markers, and sequences at eight nuclear non-coding loci and one mitochondrial gene were used to analyse population structure. The geographic distribution of variation suggests greater affinities within than among regions. The pattern of variability at both the nuclear and mitochondrial DNA (mtDNA) loci is consistent with a bottleneck, although population structure may also partly explain our results. Our results are also indicative of the role of selection, whether positive or purifying, in the mtDNA. This highlights the fact that the interfering influences of population structure, demography and selection on molecular variation are not easily distinguished.

Animals↗
PubMed1986

Shedding patterns of Schistosoma mansoni and Ribeiroia marini cercariae from a mixed infection of Biomphalaria glabrata.

When the snail Biomphalaria glabrata is doubly infected by two species of trematode, Schistosoma mansoni and Ribeiroia marini, each species keeps its own cercarial shedding pattern. Emergence of S. mansoni cercariae occurs during the photophase while the R. marini cercariae are shed during the night. These results demonstrate the absence of interference between the mechanisms responsible for the cercarial shedding of each species. The only difference noted concerns a two-hour shift in the peak emergence of S. mansoni as a consequence of the antagonism between the two parasites.

Animals↗
PubMed1989

Schistosoma rodhaini: dynamics and cercarial production for mono- and pluri-miracidial infections of Biomphalaria glabrata.

No significant difference in cercarial production was noted when Biomphalaria glabrata from Brazil were exposed to one or several miracidia of Schistosoma rodhaini from Burundi, even though the dynamics seemed different. The minor differences can be explained by the intramolluscal larval development of this parasite characterized by the production of a high number of daughter sporocysts over a long period.

Animals↗
PubMed1990

Effects of infection with Angiostrongylus cantonensis on the circulating haemocyte population and the haematopoietic organ of the host snail M-line Biomphalaria glabrata.

The number of circulating haemocytes, the size of the haematopoietic organ, and the size of haemocyte capsules around the parasite were studied in M-line Biomphalaria glabrata snails exposed to 100 or 400 first-stage larvae of Angiostrongylus cantonensis. The number of haemocytes in exposed snails increased significantly at 1 day post-exposure, decreased to control value, and then increased again. The decrease in number of circulating haemocytes is probably due to the removal of cells from the circulation to participate in encapsulation of larvae. The majority of circulating haemocytes in M-line B. glabrata are fully-spread granulocytes, which increase significantly in number in snails following exposure to A. cantonensis larvae. However, populations of partially-spread granulocytes, round cells, hyalinocytes and miscellaneous haemocytes were relatively constant. The size of capsules around the parasite increased during the 42-day interval of the experiment. The haematopoietic organ increased in size in response to infection.

Angiostrongylus↗
PubMed1992

Effect of the organophosphorous insecticide, chlorpyrifos (Dursban), on growth, fecundity and mortality of Biomphalaria alexandrina and on the production of Schistosoma mansoni cercariae in the snail.

Exposure of Biomphalaria alexandrina to sublethal concentrations (0.125, 0.25 and 0.05 ppm) of the organophosphorous insecticide, chlorpyrifos (Dursban), induced a reduction in egg production and egg hatchability. Exposure of Schistosoma mansoni miracidia to the insecticide (60 min, 0.50 ppm) prior to infection of B. alexandrina did not affect the subsequent production of cercariae. However, exposure of S. mansoni-infected snails to the insecticide until day 55, from day 20 to day 62 and from day 35 to 62 following infection resulted in blockage of cercarial shedding. Cercarial shedding commenced in some snails when the treatment stopped. Exposure to the insecticide in concentrations of 0.125 and 0.25 ppm during the first 20 days following infection did not affect the subsequent production of cercariae, but exposure to 0.5 ppm during the first 20 days affected markedly the production of cercariae due to a high snail mortality. The findings indicate that the cercaria is the target stage for the activity of chlorpyrifos on the intramolluscan larval development. It is suggested that S. mansoni cercarial production in B. alexandrina may be a useful system for monitoring the effect of low concentrations of pesticides on the aquatic environment, and that the ability by chemical means to interrupt the cercarial production might be a useful tool in further analyses of important aspects of the snail/parasite relationship.

Animals↗
PubMed1984

Experimental studies of age-prevalence curves for Schistosoma mansoni infections in populations of Biomphalaria glabrata.

We report the results of experimental studies of the generation of age-prevalence curves for Schistosoma mansoni infections in laboratory populations of Biomphalaria glabrata. Within snail populations of varying sizes and age structures, the net force of infection is shown to be linearly dependent on the rate at which miracidia are introduced into the aquatic habitat of the host. For individual snails, the per capita force of infection is shown to be related to snail age and size, and the death rate of shedding snails is demonstrated to be dependent on the period of time during which a snail has been releasing cercariae. Both factors are important determinants of the proportion of infected snails within populations of hosts and may generate convex age-prevalence curves. Comparisons of snail abundance in populations either exposed, or not exposed, to infection suggest that S. mansoni can act to significantly depress the population growth of its intermediate host. Mathematical models are developed, incorporating the age structure of snail populations, to aid in the interpretation of experimental results.

Age Factors↗
PubMed1975

Genetic factors in susceptibility of Biomphalaria glabrata for different strains of Schistosoma mansoni.

Biomphalaria glabrata selected for genetic differences in susceptibility to infection with a Puerto Rican strain of Schistosoma mansoni were exposed to miracidia of a strain of S. mansoni from St Lucia. The St Lucian strain was less infective than the Puerto Rican. Results suggested that in snails susceptible to the Puerto Rican S. mansoni differences in susceptibility to the St Lucian straing were determined by a single gene, with insusceptibility dominant.

Animals↗
PubMed1987

Biomphalaria glabrata: changes in calcium reserves following parasitism by larval Schistosoma mansoni.

Larval Schistosoma mansoni have been shown to induce morphological changes to the internal calcium reserves (in particular the calcareous inclusions in Type A calcium cells and to the inner, nacreous layer of the shell) of Biomphalaria glabrata within 48 h of miracidial penetration. Control experiments have shown that these changes were not due to either the experimental procedures used, mechanical damage or to starvation effects. The effects were, however, analogous to experimentally induced acidosis, suggesting that the rapidly transforming miracidium-sporocyst quickly induces changes in the host's metabolism, presumably by the production and release of CO2 and waste metabolites into the haemolymph.

Animals↗
PubMed1987

Transient non-susceptibility to Schistosoma mansoni associated with atrial amoebocytic accumulations in the snail host Biomphalaria glabrata.

In some Biomphalaria glabrata-Schistosoma mansoni combinations snails are susceptible to infection as juveniles, but have variable susceptibility as adults. These snails become non-susceptible at the onset of egg-laying and typically revert to susceptibility in old age. Certain stocks of B. glabrata have the capacity to form amoebocytic accumulations in the atrium, and this ability is under genetic control. The atrial amoebocytic accumulations are transitory, typically appearing at onset of egg-laying and disappearing after a few months. A snail stock which has genetic tendencies for both adult variable susceptibility and atrial amoebocytic accumulations was studied. An association between the time of occurrence of adult non-susceptibility and atrial accumulation is revealed as snails never became infected with S. mansoni when amoebocytic accumulations were present. Developing parasites, however, were not necessarily encapsulated and destroyed by amoebocytes. Some sporocysts were able to delay development until the amoebocytic accumulations disappeared. The timing of atrial amoebocytic accumulations and resulting transient non-susceptibility in this host-parasite combination could influence snail population dynamics.

Animals↗
PubMed1989

Resistance to Millettia molluscicide in Biomphalaria glabrata: a quantitative genetical approach.

This paper demonstrates the use of a quantitative genetical technique to assess genetic variance in molluscicide resistance in a Millettia thonningii-Biomphalaria glabrata system. Results indicated that there were significant genetic variances in both snail size and survival time in 10 p.p.m. molluscicide suspension. The possibility of wider applications of this technique in examining the genetic basis of molluscicide or pesticide resistance in target species is discussed.

Animals↗
PubMed1989

Spatial and temporal heterogeneity in the population dynamics of Bulinus globosus and Biomphalaria pfeifferi and in the epidemiology of their infection with schistosomes.

Populations of Bulinus globosus and Biomphalaria pfeifferi were studied in a river habitat in Zimbabwe over a period of 12 months. Data were obtained on the prevalences of infections of Schistosoma haematobium (also S. mattheei) and S. mansoni respectively. Population parameters showed the following patterns for both snail species. (1) A patchy distribution correlated with the distributions of aquatic plants. (2) Life-expectancies of only a few weeks. (3) Recruitment rates correlated with water temperature and showing a distinct seasonal peak. (4) Spatial variation in recruitment. (5) A redistribution of snails during the rainy season. Epidemiological parameters showed the following patterns. (1) Large seasonal variations in the prevalence of patent infections. (2) Evidence from size-prevalence curves that suggests a variable force-of-infection from man to snail, correlated with water temperature. (3) Prevalences of infection that were higher in the vicinity of (+/- 60 m from) major water contact sites. Local prevalences of infection for B. globosus sometimes exceeded 50% and may have approached 100% if pre-patent infections are included. Snail numbers may limit transmission at these locations. Attention is drawn to the need to make field observations at an appropriate spatial scale and also to the implications for the effectiveness of focal snail control as a means of reducing transmission.

Animals↗
PubMed1989

Effects of infection with Echinostoma paraensei on the circulating haemocyte population of the host snail Biomphalaria glabrata.

Circulating haemocytes from Echinostoma paraensei-infected M line Biomphalaria glabrata snails, or from age- and size-matched control snails, were studied on plastic slides with phase-contrast optics. Granulocytes, hyalinocytes, and round cells were consistently present; granulocytes were further categorized as 'fully spread' (FS) or 'partially spread' (PS). Among control snails, the relative percentage and estimated number/mm3 of round cells declined significantly with increased snail size, and the corresponding values for both categories of granulocytes increased. At 1 day post-infection (p.i.) with E. paraensei, overall composition of the haemocyte population was relatively unaffected, but by 8 days p.i. infected snails had significantly higher relative percentages of round cells and PS granulocytes than controls. Because a marked increase in the number of circulating haemocytes is also evident by 8 days p.i., infected snails had approximately 12 times more round cells and PS granulocytes/mm3 of haemolymph than did controls. At 30 days p.i. the relative and absolute abundance of PS granulocytes was still significantly elevated, but otherwise haemocyte populations did not differ from control snails. Alterations in granulocyte size in infected snails were also noted. Infection with E. paraensei has a striking impact of circulating haemocyte populations and also increases the relative concentration of haemocytes with less ability to adhere to a foreign surface.

Animals↗
PubMed1991

Thermal preferences of resistant and susceptible strains of Biomphalaria glabrata (Gastropoda) exposed to Schistosoma mansoni (Trematoda).

The thermal preferences of two strains of the snail Biomphalaria glabrata, one resistant to, and one susceptible to, the parasite Schistosoma mansoni were determined in an aquatic thermal gradient. Snails were tested without exposure to the parasite, and 2 h and 5 weeks after exposure to trematode miracidia. The mean temperature selected by susceptible strain snails 2 h post-exposure tended to be lower than that of unexposed controls, although this was not statistically significant. In this strain, at 5 weeks post-exposure, the preferred temperature dropped by 1.9 +/- 0.5 degree C. The resistant strain displayed a significant drop of 1.8 +/- 0.6 degree C 2 h post-exposure. These results are consistent with the hypothesis that a drop in mean temperatures selected by snails is due to altered levels of endogenous cytokines such as IL-1 or TNF in association with parasite activation of the snail internal defense system.

Animals↗
PubMed1990

Influence of larval schistosomes on polysaccharide synthesis in albumin glands of Biomphalaria glabrata.

An in vitro bioassay was used to examine [14C]glucose incorporation into polysaccharides in albumen glands (AGs) of susceptible M-line Biomphalaria glabrata infected with the NMRI strain of Schistosoma mansoni. Polysaccharide and galactogen synthesis were unaffected by larval trematode infection in AGs of snails at days 14, 21, and 28 post-infection (p.i.) when compared to uninfected controls. Further experiments were conducted to determine if daughter sporocysts, hypothesized to be primary mediators of parasitic castration in this system, were able to exert direct effects on synthetic activity of uninfected AGs via haemolymph-borne molecules or in vitro culture-generated larval excretory-secretory (ES) products. When AGs were incubated in the presence of infected snail haemolymph, significant differences in quantities of polysaccharides and galactogen were detected only in test organs incubated in day 28 p.i. haemolymph. Daughter sporocyst ES products generated during the first 48 h of culture caused a significant reduction in polysaccharide and galactogen synthesis in test organs. When ES products from days 3 to 6 of in vitro culture were tested similarly, no significant differences in either polysaccharide or galactogen synthesis were observed between control and test organs. These data demonstrate that daughter sporocysts are able to modulate a specific aspect of the reproductive activity of the snail host through haemolymph-borne molecules of host or parasite origin, or directly through in vitro culture-generated ES products.

Analysis of Variance↗