Schistosoma mansoni: axenic culture of daughter sporocysts

Cloning and functional characterization of two calmodulin genes during larval development in the parasitic flatworm Schistosoma mansoni

Schistosomiasis is endemic in over 70 countries, in which more than 200 million people are infected with the various schistosome species. Understanding the physiological processes underlying key developmental events could be useful in developing novel chemotherapeutic reagents or infection intervention strategies. Calmodulin is a small, calcium-sensing protein found in all eukaryotes and, although the protein has been previously identified in various Schistosoma mansoni stages and implicated in egg hatching and miracidia transformation, few molecular and functional data are available for this essential protein. Herein, we report the molecular cloning, expression, and functional characterization of calmodulin in the miracidia and primary sporocyst stages of S. mansoni. Two transcripts, SmCaM1 and SmCaM2, were cloned and sequenced, and a recombinant SmCaM1 protein was expressed in Escherichia coli and used to generate anti-CaM antibodies. The 2 protein sequences were highly conserved when compared to other model organisms. The alignment of the predicted proteins of both SmCaM1 and SmCaM2 exhibited 99% identity to each other and 97-98% identity with mammalian calmodulins. Analysis of steady-state transcript abundance indicate that the 2 calmodulin transcripts differ in their stage-associated expression patterns, although the CaM protein isotype appears to be constitutively expressed during early larval development. Application of RNAi to larval parasites results in a "stunted growth" phenotype in sporocysts with 30 and 35% reduction in transcript abundance for SmCaM1 and SmCaM2, respectively, and a corresponding 35% reduction in protein level after incubation in double-stranded RNA. Differential expression of CaM transcripts during early larval development and a growth defect-inducing effect associated with partial transcript and protein inhibition as a result of RNAi suggest a potentially important role of calmodulin during early larval development.

Physiologic studies of snail-schistosome interactions and potential for improvement of in vitro culture of schistosomes

Despite extensive efforts to develop suitable media for rearing the intramolluscan stages of schistosomes, successful in vitro culture of these parasites remains elusive. Recent 31P NMR studies demonstrated that the levels of free phospholipids, particularly phosphatidylcholine, in the digestive gland of the snail, Biomphalaria glabrata, were dramatically reduced when the host was infected with Schistosoma mansoni. It was speculated that absorption of host phosphatides may be an important source of membrane phospholipid precursors and fatty acids for developing sporocysts and cercariae. During the present investigations, B. glabrata was maintained on a high fat diet of egg yolk, and the lipid composition of control uninfected and infected snails examined by 31P and 13C NMR. In addition, the levels of host hemolymph metabolites, including glucose and urea, considered as indicators of parasite nutrient uptake, were monitored. The lipid level of snails fed egg yolk was greatly increased, and hosts developed patient infections in approximately half the time of infected snails maintained on lettuce. The composition of the free phospholipids accumulated in the tissues of B. glabrata fed egg yolk were the same as those previously reported in the cercarial stage of S. mansoni. Moreover, the fatty acids of S. mansoni and those reported here in the neutral lipids and free phosphatides in the host tissues were similar. Uninfected snails maintained on lettuce had higher hemolymph levels of glucose than those reared on egg yolk, and infected hosts on egg yolk had significantly lower levels of hemolymph urea. Beta-hydroxybutyrate was the principal hemolymph metabolite in snails fed egg yolk, but was not detected in snails maintained on lettuce.(ABSTRACT TRUNCATED AT 250 WORDS)