Myxozoan Minicollagen Gene Repertoire Is Not Simplified By The Parasitic Lifestyle: Computational Identification Of Novel Myxozoan Minicollagen Gene 

Background: Lineage-specific gene expansions represent one of the driving forces in the evolutionary dynamics of unique phylum traits. The obligate parasitic group of Cnidaria, Myxozoa, are evolutionarily altered and highly reduced organisms with a simple body plan including cnidarian-specific organelles, polar capsules (a type of nematocyst). A prominent constituent of nematocysts, linking Myxozoa and Cnidaria, represents a group of structural proteins, minicollagens. Despite recent advances in the identification of minicollagens in Myxozoa, the evolutionary history and diversity of minicollagens in Myxozoa and Cnidaria remain elusive. Results: We present newly generated transcriptomes of two myxozoan species with a novel pipeline for filtering of closely related contaminant species in RNA-seq data. Mining of the set of our transcriptomes and published -omics data confirmed the existence of myxozoan Ncol-4, once only reported, and we discovered a novel non-canonical type of minicollagen, Ncol-5, which is exclusive to Myxozoa. Phylogenetic analyses support a close relationship of myxozoan Ncol-1,2,3 with minicollagens of Polypodium hydriforme , however, suggest rather independent evolution in the case of two myxozoan minicollagens Ncol-4 and Ncol-5. Additional genome- and transcriptome-wide searches of cnidarian minicollagens expand the dataset to clarify better minicollagen evolutionary trajectories. Conclusions: The development of a new approach for the handling of contaminated next-generation data by closely related species represents a useful tool for future applications not only in the field of myxozoan research. This pipeline of data processing allowed us to expand the dataset and study the evolution and diversity of minicollagen gene family in Myxozoa and Cnidaria. We identified a novel type of minicollagen in Myxozoa (Ncol-5). We suggest that a high number of minicollagen paralogs in some cnidarians is a result of several recent large gene multiplication events. We revealed a close localization of minicollagens Ncol-1 and Ncol-4 in myxozoan genomes suggesting their common evolutionary history. The unique gene structure of myxozoan Ncol-5 may indicate a putative specific function in the myxozoan polar capsule or tubule. The range of myxozoan minicollagens proves that the myxozoan minicollagen gene repertoire is similar to other cnidarians and is not simplified by the parasitic lifestyle.