Morphological, biochemical, ecological and taxonomic analysis of the reversible adhesion of sea urchins from the Atlantic and Indo-Pacific

Abstract

Sea urchins tube feet produce adhesive and de-adhesive secretions, enabling strong but reversible adhesion to the substrate. Due to its potential in biotechnology, research has been conducted to study the protein and glycidic contents of the adhesive secretion, and identify the main components responsible for its adhesion and polymerization. A recent study with four sea urchin species indicated a high interspecific variability of glycans involved in adhesion, although high conservation was found between taxonomically closer species. To further confirm these results, six sea urchin species (Paracentrotus lividus, Strongylocentrotus droebachiensis, Strongylocentrotus purpuratus, Echinometra mathaei and Tripneustes gratilla and Holopneustes purpurascens) were tested for common key elements in their adhesive secretions and whether these similarities are related to their geographical distribution, habitat or taxonomy. The study aims at analysing: 1) external morphology of the tube feet through Scanning Electron Microscopy; 2) internal morphology through a variety of staining techniques on histological sections, and 3) presence of adhesive molecules through lectin histochemistry and lectin blotting, using 22 lectins. Our results showed the presence of N-acetylglucosamine (GlcNAc) conjugated glycoproteins in all species, while N-acetylgalactosamine (GalNAc) conjugated glycoproteins were found in all except T. gratilla. Contrary to the above mentioned hypothesis, it was demonstrated that at least for the six studied species: (1) the glycans present in adhesion related structures are mainly GlcNAc and GalNAc, (2) taxonomically closer species do not necessarily have glycoproteins with similar molecular weights, since species belonging to different families and orders presented protein bands with the same molecular weight, (3) no connection to the species morphology, ecology and habitat could be established. Although the two glycans have been detected in other sea urchin species and other marine attaching invertebrates, there is still a need to expand the study and consistently use a wider battery of lectins, to consolidate these results.