The genomes of four tapeworm species reveal adaptations to parasitism
The three main groups of worms parasitizing humans are tapeworms (Cestoda), flukes (Trematoda) and round worms (Nematoda). Tapeworms can parasitise almost all vertebrates. In humans, they cause severe diseases such as echinococcosis and cysticercosis, which have been prioritised as part of the neglected tropical diseases by WHO. The genomic analysis of 3 human-infective tapeworm species - Echinococcus multilocularis (fox tapeworm), Echinococcus granulosus (dog tapeworm), Taenia solium (pork tapeworm) and a laboratory model Hymenolepsis microstoma (rodent tapeworm), reveals adaptations to parasitism. Comparison with genomes of animals reveals loss of several ubiquitously present genes and pathways, including homeobox genes and determinants of stem cell fate. However, tapeworms also possess species-specific expansions of heat shock proteins and families of known antigens.
Analysis of their metabolic potential reveals an overall reduction in metabolic capacity with a concomitant increase in the ability to absorb nutrients from their hosts. For instance, they lack the genes required to synthesise fatty acids and cholesterol; however, they possess tape worm-specific gene families, such as fatty acid binding protein (FABP) and apolipoprotein antigen B, in addition to normal fatty acid transporters, to scavenge fats from the host. Tapeworms also possess specialized detoxification pathways distinct from their mammalian hosts, with an expansion of glutathione S-transferases suggesting an ability to excrete a large range of compounds.
Tsai, I.J., Zarowiecki, M., Holroyd, N., Garciarrubio, A., Sanchez-Flores, A., Brooks, K.L., Tracey, A., Bobes, R.J., Fragoso, G., Sciutto, E., Aslett, M., Beasley, H., Bennett, H.M., Cai, J., Camicia, F., Clark, R., Cucher, M., De Silva, N., Day, T.A., Deplazes, P., Estrada, K., Fernández, C., Holland, P.W.H., Hou, J., Hu, S., Huckvale, T., Hung, S.S., Kamenetzky, L., Keane, J.A., Kiss, F., Koziol, U., Lambert, O., Liu, K., Luo, X., Luo, Y., Macchiaroli, N., Nichol, S., Paps, J., Parkinson, J., Pouchkina-Stantcheva, N., Riddiford, N., Rosenzvit, M., Salinas, G., Wasmuth, J.D., Zamanian, M., Zheng, Y., The Taenia solium Genome Consortium, Cai, X., Soberón, X., Olson, P.D., Laclette, J.P., Brehm, K. and Berriman, M. (2013) The genomes of four tapeworm species reveal adaptations to parasitism. Nature.496: 57-63
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