Meeting Abstract
Genes involved in evading or coping with the host immune response underlie the genetic basis of parasitism. Understanding the evolution of genes related to blood parasitism in flatworms is of particular importance, as schistosomes (Trematoda: Schistosomatidae: Schistosoma spp.) infect 240 million people in ~78 countries, ranking as the second most devastating parasitic disease in the world. Of interest are the venom allergen-like proteins (VAPs), which are released by trematodes during infection and related to host immunomodulation. Chalmers and colleagues originally described 28 VAPs of 2 main groups consistent with phylogenetic clustering from transcripts of Schistosoma mansoni. In 2012, Chalmers and Hoffmann suggested that Group 2 VAPs are structurally and functionally conserved; whereas, Group 1 VAPs are restricted to class-specific clades and highly divergent structurally and functionally. Parasitic Group 1 VAPs may be under positive selection if divergence is driven by host-parasite interactions. Here, we expand our understanding of parasitic flatworm VAPs by including 21 new transcriptomes from non-schistosome blood flukes and 26 transcriptomes from public databases representing each parasitic flatworm class as well as free-living flatworms. We identified complete protein sequences for 578 new VAPs and recovered the phylogenetic clustering observed by Chalmers and Hoffmann, including class-specific clades within Group 1 VAPs. We also test whether these VAPs are under selection. This study is of medical relevance as it should help elucidate VAP residues important in mediating blood fluke host specificity and pathogenicity. Moreover, understanding gene family evolution and patterns of selection in genes involved in host-parasite interactions in flatworms is an important step in understanding the origin and evolution of parasitism more broadly.
