Bioadhesion of Flatworms

Synthetic adhesives are widely used in our daily lives, in medicine and industry. These man-made glues usually contain toxic or carcinogenic components. In contrast, biological adhesives produced by animals and plants are non-toxic, tissue compatible, function under wet conditions, nevertheless they perform extremely well in their natural environment. However, little is known about the mechanisms underlying biological adhesives. It is the goal to generate novel biomimetic glues for biomedicine and industrial applications. Flatworms possess a duo-gland adhesive system which allows them to rapidly attach and release from any substrate. The flatworm adhesive system consists of few to hundreds adhesive organs, composed of three cell types - an adhesive gland cell which secretes the glue, a releasing gland cell which is secreting the detachment component, and an anchor cell, a modified epidermal cell with long enforced microvilli for structural stabilization. Flatworms occur in diverse habitats from marine to freshwater environments, in calm waters but also wave exposed beaches. Certain parasitic flatworm taxa use adhesive pads with secretions to attach to the host. In the proposed project we aim identifying novel proteins that are involved in biological adhesion and release in 20 diverse flatworm species. The species are carefully selected to cover the major taxa of the Platyhelminthes. In addition, the selection encompasses species from marine, brackish, and freshwater habitats and a parasitic species which attaches to the skin of a fish using adhesive secretions. Furthermore, the selection includes species occurring in low tide regions, in high energy beaches, in lakes, in calm freshwater environments, on horseshoe crabs, in sand, under stones, or on plants. Finally, species were selected according to their availability and experimental accessibility. We hypothesize that flatworms have evolved adaptations to meet the requirements for adhesion in the respective environment. This notion is supported by the observation that one of the two adhesive proteins we identified in the flatworm Macrostomum lignano do not show any homologs in a transcriptome database of 61 other flatworm species of which data are available in public databases or form own pilot studies. In the past years we have established a state-of-the-art methodological toolbox to study bioadhesion. This approach allowed us identifying and confirming the function of two adhesive proteins and two release candidates of two marine flatworm species and the freshwater polyp Hydra. This project brings together a well-suited selection of flatworm species, a proven methodological toolbox for adhesive identification, and, together with the collaborators, leading knowledge on flatworm biology and experimentation. The results will provide a list of diverse adhesive proteins which can serve as lead sequences for the production of flatworm-inspired biomimetic glues.

Many free-living Platyhelminthes (flatworms) can attach and release very rapidly from any natural substrate. This ability makes them suitable candidates to study temporary bioadhesion. We have identified two giant adhesion proteins which mediate attachment in the marine flatworm Macrostomum lignano. Based on a broad dataset, we were able to propose a novel model of flatworm temporary adhesion. The natural habitat of M. lignano is the lagoon of Venice, Italy and the animals live on low energy beaches between sand granules. We hypothesized that flatworm species from other habitats possess adapted adhesive proteins. Therefore, in this project, it was the goal to identify adhesion proteins of diverse flatworms form diverse environments including freshwater, brackish water, and marine environments. Notably, we have not found substantial variations in the identified regions of the adhesive proteins. To further characterize the adhesive biology of flatworms we studied the morphology of adhesive organs, sequenced all genes (transcriptomes) of several species, analysed the expression of the adhesive proteins (in situ hybridization) and switched off the production of the proteins (RNA interference) to study their involvement in the adhesion process. Due to the large size of the adhesive proteins, it was a challenge to identify their full amino acid sequence. For that reason, we established Oxford Nanopore long-read sequencing in the lab. Using this technology, it was possible to characterize the full length of the adhesive proteins. Commercial adhesives are often toxic and carcinogenic, might trigger allergies, and can cause environmental problems. Moreover, synthetic adhesives show a limited performance under wet conditions, especially in medical applications. In contrast, biological adhesives are biocompatible, biodegradable, non-toxic, and capable of adhering to a variety of surfaces, including underwater environments. Notably, flatworm glues are reversible: they can detach very rapidly and voluntarily from all natural surfaces. Therefore, biological reversible adhesives can fulfil the needs for novel glues in both industry and biomedicine. The findings of this project can help to find new adhesive proteins sequences for the generation synthetic adhesives for medical or industrial applications.