title: Comparative gene analysis of Biomphalaria glabrata hemocytes pre- and post-exposure to miracidia of Schistosoma mansoni.
abstract: The internal defense mechanism of the snail Biomphalaria glabrata during a schistosome infection is activated and mediated via the immune effector cells known as hemocytes. Since resistance and susceptibility to schistosome infection is known to be genetically determined, our interest was to use the EST approach as a gene discovery tool to examine transcription profiles in hemocytes of resistant snails pre- and post-exposure to Schistosoma mansoni. Comparative analysis of the transcripts suggested that parasite exposure caused an active metabolic response in the hemocytes. The most abundant transcripts were those showing 23-74% similarity to known reverse transcriptases (RT). Further characterization by RT-PCR indicated the RT transcripts were expressed in normal snails, parasite exposed snails, and the embryonic cell line Bge. To determine whether the occurrence of RT transcripts correlates to the presence of functional enzyme activity in the snails, RT assays were performed from both resistant and susceptible snails, pre- and post-exposure to miracidia, using protein extracts from the head-foot and posterior region tissues. Results indicated that in the resistant snail, RT activity was greater in the posterior region than in the head-foot. After exposure, however, RT activity increased dramatically in the head-foot, with peak activity at 24 h post-exposure. The detection of RT activity in B. glabrata was unexpected and the role of this enzyme in the hemocyte-mediated killing of parasites is not yet known. However, identification of this and other transcripts from these cells by the EST approach provides a useful resource towards elucidating the molecular basis of resistance/susceptibility in this snail-host parasite relationship.
authors.affiliation: Biomedical Research Institute, Rockville, MD 20852, USA.
authors.forename: Nithya
authors.initials: N
authors.lastname: Raghavan
authors.forename: Andre N
authors.initials: AN
authors.lastname: Miller
authors.forename: Malcolm
authors.initials: M
authors.lastname: Gardner
authors.forename: Peter C
authors.initials: PC
authors.lastname: FitzGerald
authors.forename: Anthony R
authors.initials: AR
authors.lastname: Kerlavage
authors.forename: David A
authors.initials: DA
authors.lastname: Johnston
authors.forename: Fred A
authors.initials: FA
authors.lastname: Lewis
authors.forename: Matty
authors.initials: M
authors.lastname: Knight
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001700:Biomphalaria / Q000201:enzymology / Q000235:genetics* / Q000469:parasitology; D015139:Blotting, Southern; D002460:Cell Line; D002938:Ciona intestinalis / Q000201:enzymology / Q000235:genetics; D020224:Expressed Sequence Tags; D006434:Hemocytes / Q000469:parasitology* / Q000502:physiology; D008969:Molecular Sequence Data; D012194:RNA-Directed DNA Polymerase / Q000737:chemistry / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012550:Schistosoma mansoni / Q000472:pathogenicity*; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D014158:Transcription, Genetic
chemical_list: D012194:RNA-Directed DNA Polymerase