Developmentally regulated expression, alternative splicing and distinct sub-groupings in members of the Schistosoma mansoni venom allergen-like (SmVAL) gene family

Background: The Sperm-coating protein/Tpx-1/Ag5/PR-1/Sc7 (SCP/TAPS) domain is foundacross phyla and is a major structural feature of insect allergens, mammalian sperm proteins andparasitic nematode secreted molecules. Proteins containing this domain are implicated in diversebiological activities and may be important for chronic host/parasite interactions.

Results: We report the first description of an SCP/TAPS gene family (Schistosoma mansoni venomallergen-like (SmVALs)) in the medically important Platyhelminthes (class Trematoda) and describeindividual members' phylogenetic relationships, genomic organization and life cycle expressionprofiles. Twenty-eight SmVALs with complete SCP/TAPS domains were identified and comparisonof their predicted protein features and gene structures indicated the presence of two distinct subfamilies(group 1 & group 2). Phylogenetic analysis demonstrated that this group 1/group 2 split iszoologically widespread as it exists across the metazoan sub-kingdom. Chromosomal localisationand PCR analysis, coupled to inspection of the current S. mansoni genomic assembly, revealed thatmany of the SmVAL genes are spatially linked throughout the genome. Quantitative lifecycleexpression profiling demonstrated distinct SmVAL expression patterns, including transcriptsspecifically associated with lifestages involved in definitive host invasion, transcripts restricted tolifestages involved in the invasion of the intermediate host and transcripts ubiquitously expressed.Analysis of SmVAL6 transcript diversity demonstrated statistically significant, developmentallyregulated, alternative splicing.

Conclusion: Our results highlight the existence of two distinct SCP/TAPS protein types withinthe Platyhelminthes and across taxa. The extensive lifecycle expression analysis indicates severalSmVAL transcripts are upregulated in infective stages of the parasite, suggesting that theseparticular protein products may be linked to the establishment of chronic host/parasiteinteractions.