Abstract
BackgroundEpendymins were originally defined as fish-specific secreted glycoproteins involved in central nervous system plasticity and memory formation. Subsequent research revealed that these proteins represent a fish-specific lineage of a larger ependymin-related protein family (EPDRs). EPDRs have now been identified in a number of bilaterian animals and have been implicated in diverse non-neural functions. The recent discoveries of putative EPDRs in unicellular holozoans and an expanded EPDR family with potential roles in conspecific communication in crown-of-thorns starfish suggest that the distribution and diversity of EPDRs is significantly broader than currently understood.ResultsWe undertook a systematic survey to determine the distribution and evolution of EPDRs in eukaryotes. In addition to Bilateria, EPDR genes were identified in Cnidaria, Placozoa, Porifera, Choanoflagellatea, Filasterea, Apusozoa, Amoebozoa, Charophyta and Percolozoa, and tentatively in Cercozoa and the orphan group Malawimonadidae. EPDRs appear to be absent from prokaryotes and many eukaryote groups including ecdysozoans, fungi, stramenopiles, alveolates, haptistans and cryptistans. The EPDR family can be divided into two major clades and has undergone lineage-specific expansions in a number of metazoan lineages, including in poriferans, molluscs and cephalochordates. Variation in a core set of conserved residues in EPDRs reveals the presence of three distinct protein types; however, 3D modelling predicts overall protein structures to be similar.ConclusionsOur results reveal an early eukaryotic origin of the EPDR gene family and a dynamic pattern of gene duplication and gene loss in animals. This research provides a phylogenetic framework for the analysis of the functional evolution of this gene family.
Highlights
Ependymins were originally defined as fish-specific secreted glycoproteins involved in central nervous system plasticity and memory formation
Phylogenetic distribution of ependymin-related protein (EPDR) The ependymin gene family is represented in the Pfam database (PF00811) [31], where an estimation of its distribution is provided based upon searches of reference proteomes from the UniProt database [32]
The clade membership and profile membership of each group is indicated in the schematic on the right case of Dictyostelium discoideum, by the presence of the EPDR gene on a scaffold containing other D. discoideum genes
Summary
Ependymins were originally defined as fish-specific secreted glycoproteins involved in central nervous system plasticity and memory formation. Long believed to be fish-specific, subsequent discoveries of ependymin-related proteins (EPDRs) in mammals [named ‘mammalian ependymin-related proteins’ (MERPS) [4] or in humans 'upregulated in colorectal cancer gene-1' (UCC1) [5]], amphibians [4] and echinoderms [6] demonstrated that the distribution of the gene family was much broader than originally thought. These studies revealed that EPDRs might perform roles outside the central nervous system. The expression of these EPDR genes in non-brain tissues and the implication of their involvement in diverse processes indicated that the functional diversity of this protein family had been underestimated
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