| dc.description.abstract-translated | The evolutionary aspects of cystatins are greatly underexplored in early-emerging metazoans.
Thus, we surveyed the gene organization, protein architecture, and phylogeny of cystatin
homologues mined from 110 genomes and the transcriptomes of 58 basal metazoan species,
encompassing free-living and parasite taxa of Porifera, Placozoa, Cnidaria (including
Myxozoa), and Ctenophora. We found that the cystatin gene repertoire significantly differs
among phyla, with stefins present in most of the investigated lineages but with type 2 cystatins
missing in several basal metazoan groups. Similar to liver and intestinal flukes, myxozoan
parasites possess atypical stefins with chimeric structure that combine motifs of classical
stefins and type 2 cystatins. Other early metazoan taxa regardless of lifestyle have only the
classical representation of cystatins and lack multi-domain ones. Our comprehensive
phylogenetic analyses revealed that stefins and type 2 cystatins clustered into taxonomically
defined clades with multiple independent paralogous groups, which probably arose due to
gene duplications. The stefin clade split between the subclades of classical stefins and the
atypical stefins of myxozoans and flukes. Atypical stefins represent key evolutionary
innovations of the two parasite groups for which their origin might have been linked with
ancestral gene chimerization, obligate parasitism, life cycle complexity, genome reduction,
and host immunity. | eng |
