Molecular characterisation of intermediate snail hosts and the search for resistance genes

The relationship between schistosomes and their intermediate hosts is an extremely intricate one with strains and species of the parasite depending on particular species of snail, which in turn may vary in their susceptibility to the parasites. In order to gain a better understanding of the epidemiology of the disease we have been investigating the use of molecular markers for snail identification and for studying host-parasite relationships. In this paper we will draw on examples concerning schistosomiasis in West and East Africa to illustrate how a molecular analysis can be used as part of a "total evidence" approach to characterisation of Bulinus species and provide insights into parasite transmission. Particular emphasis is given to ribosomal RNA genes (rRNA), random amplified polymorphic DNA (RAPDs) and the mitochondrial gene cytochrome oxidase I (COI). Snails resistant to infection occur naturally and there is a genetic basis for this resistance. In Biomphalaria glabrata resistance to Schistosoma mansoni is known to be a polygenic trait and we have initiated a preliminary search for snail genomic regions linked to, or involved in, resistance by using a RAPD based approach in conjunction with progeny pooling methods. We are currently characterising a variety of STSs (sequence tagged sites) associated with resistance. These can be used for local linkage and interval mapping to define genomic regions associated with the resistance trait. The development of such markers into simple dot-blot or specific PCR-based assays may have a direct and practical application for the identification of resistant snails in natural populations

An unusual evolutionary strategy: the origins, genetic repertoire, and implications of doubly uniparental inheritance of mitochondrial DNA in bivalves

International audienceMitochondrial DNA (mtDNA) is typically passed on to progeny only by the female parent. The phenomenon of "doubly uniparental inheritance" (DUI) of mtDNA in many bivalve species is a fascinating exception to the paradigm of strict maternal inheritance of mtDNA. In this review, we survey the current state of knowledge of DUI, and discuss several active areas of research in this field. Topics/questions covered include: the number of times DUI evolved (once or multiple origins), the link between DUI and sex determination, the role(s) of mtDNA-encoded non-oxidative phosphorylation genes (i.e., ORFan/orf genes) in freshwater mussels, the function of conserved sequence motifs and sperm transmission elements in mtDNA of marine mussels, the challenges of annotating mtDNA genomes of DUI species, the presence of unorthodox features in venerid mtDNA, whether or not orf DNA sequences are useful in species-level identification of freshwater mussel, and finally, whether or not there are obvious benefits of DUI. For each topic we also highlight important avenues for future research within this fascinating field of mitochondrial evolutionary biology