Abstract
BackgroundCestoda is a class of endoparasitic worms in the flatworm phylum (Platyhelminthes). During the course of their evolution cestodes have evolved some interesting aspects, such as their increased reproductive capacity. In this sense, they have serial repetition of their reproductive organs in the adult stage, which is often associated with external segmentation in a developmental process called strobilation. However, the molecular basis of strobilation is poorly understood. To assess this issue, an evolutionary comparative study among strobilated and non-strobilated flatworm species was conducted to identify genes and proteins related to the strobilation process.ResultsWe compared the genomic content of 10 parasitic platyhelminth species; five from cestode species, representing strobilated parasitic platyhelminths, and five from trematode species, representing non-strobilated parasitic platyhelminths. This dataset was used to identify 1813 genes with orthologues that are present in all cestode (strobilated) species, but absent from at least one trematode (non-strobilated) species. Development-related genes, along with genes of unknown function (UF), were then selected based on their transcriptional profiles, resulting in a total of 34 genes that were differentially expressed between the larval (pre-strobilation) and adult (strobilated) stages in at least one cestode species. These 34 genes were then assumed to be strobilation related; they included 12 encoding proteins of known function, with 6 related to the Wnt, TGF-β/BMP, or G-protein coupled receptor signaling pathways; and 22 encoding UF proteins. In order to assign function to at least some of the UF genes/proteins, a global gene co-expression analysis was performed for the cestode species Echinococcus multilocularis. This resulted in eight UF genes/proteins being predicted as related to developmental, reproductive, vesicle transport, or signaling processes.ConclusionsOverall, the described in silico data provided evidence of the involvement of 34 genes/proteins and at least 3 developmental pathways in the cestode strobilation process. These results highlight on the molecular mechanisms and evolution of the cestode strobilation process, and point to several interesting proteins as potential developmental markers and/or targets for the development of novel antihelminthic drugs.
Highlights
Cestoda is a class of endoparasitic worms in the flatworm phylum (Platyhelminthes)
11,300 orthogroups of deduced protein sequences were identified, of which 285 have orthologous genes in all 18 analyzed species. These 285 protein sets were aligned, and the alignments were concatenated in a supermatrix for phylogenomic inference via Bayesian analysis
The platyhelminthes were clearly divided into two clades, one with external body segmentation and the other with only internal segmentation
Summary
During the course of their evolution cestodes have evolved some interesting aspects, such as their increased reproductive capacity In this sense, they have serial repetition of their reproductive organs in the adult stage, which is often associated with external segmentation in a developmental process called strobilation. Platyhelminths (flatworms) are dorsoventrally flattened bilaterian acoelomates that lack an anus, possess a low level of cephalization, and are usually hermaphroditic [1]. They are divided into four main classes: Turbellaria (free-living planarians), Monogenea (mostly aquatic ectoparasites), Trematoda (flukes), and Cestoda (tapeworms) [2]. The World Health Organization’s list of neglected tropical diseases (http:// www.who.int/neglected_diseases/diseases/en/) includes several caused by endoparasitic flatworms, namely foodborne trematodiases (caused by Clonorchis spp. and Fasciola spp., among other flukes), schistosomiases (caused by Schistosoma spp.), echinococcoses (caused by Echinococcus spp.), and taeniases/cysticercosis (caused by Taenia spp.)
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