The growing repertoire of putative pathogen interaction genes in the Biomphalaria glabrata vs Schistosoma mansoni system.

Schistosomiasis is major neglected tropical disease of humans that is caused by trematodes in the genus Schistosoma. Humans are infected during contact with water in which schistosomes are being shed from their intermediate hosts, freshwater snails. Snail control is effective at reducing transmission, but can be expensive and ecologically problematic. Therefore, there is substantial interest in understanding the genetic mechanisms behind variation in snail resistance to infection by schistosomes, with the goal of leveraging that information to reduce transmission at the snail stage. Biomphalaria glabrata is an important host snail for transmission of S. mansoni in the New World. Here we reanalyzed an older Genome-Wide Association Study (GWAS) dataset from Biomphalaria glabrata snails challenged by the trematode, Schistosoma mansoni. We identified two new regions of association with resistance to infection, named LG5R and LG11L. LG11L contains a cluster of genes for a diverse set of secreted lectins, which could be involved in some type of recognition. LG5R contains a cluster of genes for what appear to be membrane-bound receptors. These genes are very similar to those identified in an adjacent genomic region by a recent GWAS on the African snail, B. sudanica challenged by S. mansoni. Clusters of genes for single-pass transmembrane proteins also characterize two other genomic regions of association with resistance to S. mansoni that were previously described for B. glabrata (the PTC1/GRC and PTC2 regions). We hypothesize that the proteins coded for in such clusters of genes are involved in some type of matching polymorphism that may explain the ubiquitous parasite-population by snail-population interaction in compatibility that characterizes the B. glabrata-S. mansoni system. We discuss our results in light of the state of the field of genome-wide mapping studies on Biomphalaria sp., and discuss what types of loci found to date would be the best targets for reducing transmission in natural populations.