title: Parasite-responsive IgSF members in the snail Biomphalaria glabrata: characterization of novel genes with tandemly arranged IgSF domains and a fibrinogen domain.
abstract: Two novel genes of the immunoglobulin superfamily (IgSF), FREP3 and FREP7, are reported from the snail Biomphalaria glabrata, a prominent intermediate host of the human parasite Schistosoma mansoni. They resemble other B. glabrata genes that encode fibrinogen-related proteins (FREPs), but differ in that they encode proteins with two tandemly arranged IgSF domains followed by a C-terminal fibrinogen domain. FREPs are hemolymph proteins that increase in abundance following exposure to a digenetic trematode, Echinostoma paraensei, and that bind to and precipitate parasite antigens. Within each gene, the two IgSF-coding regions are dissimilar from one another: the N-terminal IgSF1 domain is encoded by a single exon whereas the downstream IgSF2 domain is encoded by three exons. For both FREPs 3 and 7, the IgSF2 domain belongs to the variable (V) type, whereas the IgSF1 domain is not easily classified with respect to IgSF type. The fibrinogen-encoding region in both genes is relatively conserved and lacks introns. FREP3 exhibits extensive variation in the IgSF1 region. A ratio of nonsynonymous versus synonymous substitutions of 2.56 suggests that this region is under positive selection. A genomic fragment identifiable as FREP7 but lacking an exon was also found, further suggestive of variability within FREP IgSF-encoding regions. Insofar as FREPs are hypothesized to function in nonself recognition, the identification of additional novel FREP genes as part of a growing gene family in B. glabrata is of interest. Such genes, particularly given their variable nature, serve as a model to study the complexity of invertebrate defense responses.
authors.affiliation: Department of Biology, University of New Mexico, Albuquerque, NM 87131, USA.
authors.forename: S M
authors.initials: SM
authors.lastname: Zhang
authors.forename: P M
authors.initials: PM
authors.lastname: Léonard
authors.forename: C M
authors.initials: CM
authors.lastname: Adema
authors.forename: E S
authors.initials: ES
authors.lastname: Loker
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D005091:Exons / Q000235:genetics; D005340:Fibrinogen / Q000737:chemistry*; D007136:Immunoglobulins / Q000737:chemistry* / Q000235:genetics / Q000276:immunology*; D007438:Introns / Q000235:genetics; D037102:Lectins / Q000737:chemistry / Q000235:genetics / Q000276:immunology; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction; D011110:Polymorphism, Genetic / Q000235:genetics; D017434:Protein Structure, Tertiary; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012045:Regulatory Sequences, Nucleic Acid / Q000235:genetics; D020449:Repetitive Sequences, Amino Acid / Q000235:genetics; D012550:Schistosoma mansoni / Q000276:immunology*; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D012908:Snails / Q000235:genetics* / Q000276:immunology* / Q000469:parasitology; D024363:Transcription Initiation Site
chemical_list: D007136:Immunoglobulins; D037102:Lectins; D012333:RNA, Messenger; C445539:fibrinogen-related protein 3, Biomphalaria glabrata; C445540:fibrinogen-related protein 7, Biomphalaria glabrata; D005340:Fibrinogen