Sticking Together an Updated Model for Temporary Adhesion

Abstract

Non-parasitic flatworms are known to temporarily attach to the substrate by secreting a multicomponent bioadhesive to counteract water movements. However, to date, only species of two higher-level flatworm taxa (Macrostomorpha and Proseriata) have been investigated for their adhesive proteins. Remarkably, the surface-binding protein is not conserved between flatworm taxa. In this study, we sequenced and assembled a draft genome, as well as a transcriptome, and generated a tail-specific positional RNA sequencing dataset of the polyclad Theama mediterranea. This led to the identification of 15 candidate genes potentially involved in temporary adhesion. Using in situ hybridisation and RNA interference, we determined their expression and function. Of these 15 genes, 4 are homologues of adhesion-related genes found in other flatworms. With this work, we provide two novel key components on the flatworm temporary adhesion system. First, we identified a Kringle-domain-containing protein (Tmed-krg1), which was expressed exclusively in the anchor cell. This in silico predicted membrane-bound Tmed-krg1 could potentially bind to the cohesive protein, and a knockdown led to a non-adhesive phenotype. Secondly, a secreted tyrosinase (Tmed-tyr1) was identified, which might crosslink the adhesive proteins. Overall, our findings will contribute to the future development of reversible synthetic glues with desirable properties for medical and industrial applications.

The Involvement of Cell-Type-Specific Glycans in Hydra Temporary Adhesion Revealed by a Lectin Screen

“…Glycosylation could also enhance protein-binding ability and make proteins more resistant to degradation [ 6 ]. There is a high variability of glycans in the adhesive material found in between species [ 6 , 10 , 11 , 32 , 33 ]. Even in animals of the same phylum, the adhesive glycan composition is variant.…”

“…Adhesion-related glycans have mostly been detected through histological stains such as Alcain blue and lectin-binding assays [ 2 ]. Using lectin-based methods, glycans have consistently been detected in the adhesive of non-permanently adhering animals such as sea urchins [ 5 , 6 ], sea stars [ 7 , 8 ], flatworms [ 9 , 10 , 11 ], and limpets [ 12 ]. Moreover, aquatic adhesive proteins are often highly glycosylated [ 5 , 6 , 7 , 13 , 14 ].…”

Glycoproteins Involved in Sea Urchin Temporary Adhesion

“…Most of the biomimetic adhesives developed so far thus rely on DOPA chemistry [ 1 , 2 ]. More recently, other organisms relying on permanent adhesion, such as tubeworms and barnacles, and temporary adhesion, such as sea stars, have also been used as models since their adhesive protein sequences have become available [ 3 , 4 , 5 ]. In addition to L-DOPA, which was only described in permanent adhesion, protein post-translational modifications (PTMs) might also play a role in wet adhesion [ 6 ].…”

“…Sugar moieties are present in the adhesive secretory cells and/or adhesive material of other reversibly-attaching aquatic animals, not restricted to Echinodermata. In flatworms such as Macrostomum lignano , the adhesive protein (Mlig-ap2) is glycosylated [ 8 , 21 , 22 , 23 ] and it was visualized in the adhesive granules and the footprint using peanut agglutinin lectin (PNA, that binds, with high specificity, the sugar galactosyl (β-1,3) N-acetylgalactosamine) histochemistry [ 5 , 8 ]. Similar results were obtained in other species, such as the proseriate M. ileanae [ 24 ].…”