Cestodes in the genomic era

Abstract

The first cestode genomes were obtained by an international consortium led by the Wellcome Sanger Institute that included representative institutions from countries where the sequenced parasites have been studied for decades, in part because they are etiological agents of endemic diseases (Argentina, Uruguay, Mexico, Canada, UK, Germany, Switzerland, Ireland, USA, Japan, and China). After this, several complete genomes were obtained reaching 16 species to date. Cestode genomes have smaller relative size compared to other animals including free-living flatworms. Moreover, the features genome size and repeat content seem to differ in the two analyzed orders. Cyclophyllidean species have smaller genomes and with fewer repetitive content than Diphyllobothriidean species. On average, cestode genomes have 13,753 genes with 6 exons per gene and 41% GC content. More than 5,000 shared cestode proteins were accurately annotated by the integration of gene predictions and transcriptome evidence being more than 40% of these proteins of unknown function. Several gene losses and reduction of gene families were found and could be related to the extreme parasitic lifestyle of these species. The application of cutting-edge sequencing technology allowed the characterization of the terminal sequences of chromosomes that possess unique characteristics. Here, we review the current status of knowledge of complete cestode genomes and place it within a comparative genomics perspective. Multidisciplinary work together with the implementation of new technologies will provide valuable information that can certainly improve our chances to finally eradicate or at least control diseases caused by cestodes.