(Un)expected Similarity of the Temporary Adhesive Systems of Marine, Brackish, and Freshwater Flatworms.

Philip Bertemes,Sara Tomaiuolo,Robert Pjeta,Birgit Lengerer,Michael W Hess,Nikolas Andresen,Bernhard Egger,Kevin Grüner,Birte Mertens,Willi Salvenmoser,Armin Zankel,Julia Wunderer,Peter Ladurner,Magdalena Knapp,Patrik Holzer,Alexandra L Grosbusch

doi:10.3390/ijms222212228

Abstract

Many free-living flatworms have evolved a temporary adhesion system, which allows them to quickly attach to and release from diverse substrates. In the marine Macrostomum lignano, the morphology of the adhesive system and the adhesion-related proteins have been characterised. However, little is known about how temporary adhesion is performed in other aquatic environments. Here, we performed a 3D reconstruction of the M. lignano adhesive organ and compared it to the morphology of five selected Macrostomum, representing two marine, one brackish, and two freshwater species. We compared the protein domains of the two adhesive proteins, as well as an anchor cell-specific intermediate filament. We analysed the gene expression of these proteins by in situ hybridisation and performed functional knockdowns with RNA interference. Remarkably, there are almost no differences in terms of morphology, protein regions, and gene expression based on marine, brackish, and freshwater habitats. This implies that glue components produced by macrostomids are conserved among species, and this set of two-component glue functions from low to high salinity. These findings could contribute to the development of novel reversible biomimetic glues that work in all wet environments and could have applications in drug delivery systems, tissue adhesives, or wound dressings.

Highlights

Bioadhesion can be found across many phyla throughout the tree of life [1,2,3]
We explored whether the ecological conditions of the habitat affect the morphology of the adhesive system and the proteins involved in the adhesion of different macrostomid species
We observed that Macrostomum species occurring in marine, brackish water, and freshwater environments all possess a highly similar organisation of the adhesive system

Summary

Introduction

Bioadhesion can be found across many phyla throughout the tree of life [1,2,3]. Different strategies evolved to perform such an important task in terrestrial environments, e.g., mechanical adhesion through little hooks such as in the plant Arctium [4], biofilms produced by bacteria to provide a habitat in otherwise unsuitable terrain [5], adhesion relying on the physical properties of the van der Waals forces is used by the gecko [6], or silks produced by spiders and other arthropods [7]. Many species have developed glues to anchor the animal permanently to the substrate in rough marine conditions, e.g., mussels, which rely on a modified amino acid tyrosine (3,4-dihydroxyphenyl-L-alanine; DOPA) in a very low pH environment [8,9,10]. In contrast to these permanently adhering animals, many aquatic invertebrates, such as echinoderms, flatworms, and limpets, evolved a non-permanent adhesion system [11,12,13]. Free-living flatworms are intriguing model systems to study non-permanent adhesion, as they occur in diverse aquatic habitats, are easy to culture, and many molecular biology tools are available for selected species

Methods

Results

Conclusion