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Studies on the biology of Schistosoma margrebowiei include, a simple means of culturing and infecting Bulinus natalensis snails; the morphology and ultrastructure of various stages in the life-cycle; pathology; cercarial longevity and infectivity; cross-reactivity with S. mansoni rabbit anti-sera and the possible use of S. margrebowiei egg homogenate in the serodiagnosis of S. haematobium patients. A simple method of maintenance and infection of B. natalensis snails en masse, was found to yield a rapid and continuous supply of material. The results indicate that the size of snails at the time of exposure is an important factor in successful infection. A wide range of morphological and ultrastructural similarities were found between S. margrebowiei larval stages and those of other species of the genus. Whereas the adult worms are among the largest, the eggs, miracidia and cercariae of S. margrebowiei, are among the smallest in the genus. The pathology associated with S. margrebowiei, is due to deposition of large numbers of eggs in various organs of the infected animal. Eggs were not only recovered from the liver and intestine but following 50 days post-infection, from the spleen. A large number (10-15%) of the total eggs recovered from mice 45 to 65 days post-infection were deposited in the spleen. The cercariae of S. margrebowiei by utilizing their glycogen reserves, can live for up to 70 hours in fresh water at temperatures of 26-28°C. This observed life-span can be prolonged when water temperatures were decreased to 8-12 °C. Cercariae kept in cold water although physically active and still infective, were found to be attenuated as measured by a reduced percentage of recovered worms compared with controls. The potential for immunizing mice with the hepatopancreas from infected and uninfected snails against schistosomiasis has been evaluated using S. mansoni. Although a reduction in the number of worms and eggs was observed in mice immunized with infected hepatopancreas when compared to the controls, this decrease was not significant. Sera from 53 patients infected with schistosomiasis were studied by ELISA using S. margrebowiei crude soluble egg antigen (SEA), S. mansoni SEA and cationic S. mansoni egg antigen (CEF6). It was found that S. margrebowiei SEA was more specific for the identification of S. haematobium infections.

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Site selection, and the means to access specific sites, is a keystone of parasitology. I evaluated migration and site selection behaviours of metacercariae of two congeneric species of strigeoid trematode throughout growth and encystment phases in the fathead minnow. Results showed that pre-encystment stages of Ornithodiplostomum ptychocheilus migrate along specific neural tracts to access sites in the optic lobes of the brain. Conversely, pre-encystment stages of Ornithodiplostomum sp. migrate via direct penetration, or via the vascular system to access visceral organs, especially the liver. Remarkably, both species have a bi-phasic pattern of development, with growth and encystment occurring in unique sites. Finally, I examined patterns of rodlet cell proliferation and maturation in response to growth and encystment phases of O. ptychocheilus. Cell densities were low (<11/mm2) in brain tissue adjacent to 1 and 2 week old metacercaria, but peaked to approximately 210/mm2 at 6 weeks. These results shed new light on the potential function of these enigmatic cells. / x, 125 leaves : ill. ; 29 cm.

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Indiana University-Purdue University Indianapolis (IUPUI) / Histone acetylation has been linked to developmental changes in gene expression and is a validated drug target of apicomplexan parasites, but little is known about the roles of individual histone modifying enzymes and how they are recruited to target genes. The protozoan parasite Toxoplasma gondii (phylum Apicomplexa) is unusual among invertebrates in possessing two GCN5-family lysine acetyltransferases (KATs). While GCN5a is required for gene expression in response to alkaline stress, this KAT is dispensable for parasite proliferation in normal culture conditions. In contrast, GCN5b cannot be disrupted, suggesting it is essential for Toxoplasma viability. To further explore the function of GCN5b, we generated clonal parasites expressing an inducible HA-tagged form of GCN5b containing a point mutation that ablates enzymatic activity (E703G). Stabilization of this dominant-negative form of GCN5b was mediated through ligand-binding to a destabilization domain (dd) fused to the protein. Induced accumulation of the ddHAGCN5b(E703G) protein led to a rapid arrest in parasite replication. Growth arrest was accompanied by a decrease in histone H3 acetylation at specific lysine residues as well as reduced expression of GCN5b target genes in GCN5b(E703G) parasites, which were identified using chromatin immunoprecipitation coupled with microarray hybridization (ChIP-chip). We also demonstrate that GCN5b interacts with AP2-domain proteins, which are plant-like transcription factors in Apicomplexa. The interactions between GCN5b, AP2IX-7, and AP2X-8 were confirmed by reciprocal co-immunoprecipitation and revealed a “core complex” that includes the co-activator ADA2-A, TFIID subunits, LEO1 polymerase-associated factor (Paf1) subunit, and RRM proteins. The dominant-negative phenotype of ddHAGCN5b(E703G) parasites, considered with the proteomics and ChIP-chip data, indicate that GCN5b plays a central role in transcriptional and chromatin remodeling complexes. We conclude that GCN5b has a non-redundant and indispensable role in regulating gene expression required during the Toxoplasma lytic cycle.