title: Genomic insights into the evolutionary origin of Myxozoa within Cnidaria.
abstract: The Myxozoa comprise over 2,000 species of microscopic obligate parasites that use both invertebrate and vertebrate hosts as part of their life cycle. Although the evolutionary origin of myxozoans has been elusive, a close relationship with cnidarians, a group that includes corals, sea anemones, jellyfish, and hydroids, is supported by some phylogenetic studies and the observation that the distinctive myxozoan structure, the polar capsule, is remarkably similar to the stinging structures (nematocysts) in cnidarians. To gain insight into the extreme evolutionary transition from a free-living cnidarian to a microscopic endoparasite, we analyzed genomic and transcriptomic assemblies from two distantly related myxozoan species, Kudoa iwatai and Myxobolus cerebralis, and compared these to the transcriptome and genome of the less reduced cnidarian parasite, Polypodium hydriforme. A phylogenomic analysis, using for the first time to our knowledge, a taxonomic sampling that represents the breadth of myxozoan diversity, including four newly generated myxozoan assemblies, confirms that myxozoans are cnidarians and are a sister taxon to P. hydriforme. Estimations of genome size reveal that myxozoans have one of the smallest reported animal genomes. Gene enrichment analyses show depletion of expressed genes in categories related to development, cell differentiation, and cell-cell communication. In addition, a search for candidate genes indicates that myxozoans lack key elements of signaling pathways and transcriptional factors important for multicellular development. Our results suggest that the degeneration of the myxozoan body plan from a free-living cnidarian to a microscopic parasitic cnidarian was accompanied by extreme reduction in genome size and gene content.
authors.affiliation: Department of Ecology and Evolutionary Biology, University of Kansas, Lawrence, KS 66045;
authors.forename: E Sally
authors.initials: ES
authors.lastname: Chang
authors.affiliation: Department of Zoology, George S. Wise Faculty of Life Sciences, Tel-Aviv University, Tel-Aviv 6997801, Israel; Department of Neurobiology, George S. Wise Faculty of Life Sciences, Tel-Aviv University, Tel-Aviv 6997801, Israel;
authors.forename: Moran
authors.initials: M
authors.lastname: Neuhof
authors.affiliation: Department of Molecular and Cellular Biology, Harvard University, Cambridge, MA 02138;
authors.forename: Nimrod D
authors.initials: ND
authors.lastname: Rubinstein
authors.affiliation: National Center for Mariculture, Israel Oceanographic and Limnological Research, Eilat 88112, Israel;
authors.forename: Arik
authors.initials: A
authors.lastname: Diamant
authors.affiliation: CNRS, Station d'Ecologie Expérimentale du CNRS, Moulis 09200, France; Département de Biochimie, Centre Robert-Cedergren, Université de Montréal, Montréal, QC, Canada H3C 3J7.
authors.forename: Hervé
authors.initials: H
authors.lastname: Philippe
authors.affiliation: Department of Zoology, George S. Wise Faculty of Life Sciences, Tel-Aviv University, Tel-Aviv 6997801, Israel; pcart@ku.edu huchond@post.tau.ac.il.
authors.forename: Dorothée
authors.initials: D
authors.lastname: Huchon
authors.affiliation: Department of Ecology and Evolutionary Biology, University of Kansas, Lawrence, KS 66045; pcart@ku.edu huchond@post.tau.ac.il.
authors.forename: Paulyn
authors.initials: P
authors.lastname: Cartwright
mesh_terms: D000818:Animals; D019143:Evolution, Molecular; D016678:Genome; D023281:Genomics; D055766:Myxobolus / Q000235:genetics*; D010802:Phylogeny; D032494:Polypodium / Q000469:parasitology
keywords: Cnidaria; Myxozoa; Polypodium; genome evolution; parasite