Abstract
BackgroundBarnacles are sessile crustaceans that attach to underwater surfaces using barnacle cement proteins. Barnacles have a calcareous or chitinous membranous base, and their substratum varies from biotic (e.g. corals/sponges) to abiotic surfaces. In this study, we tested the hypothesis that the cement protein (CP) composition and chemical properties of different species vary according to the attachment substrate and/or the basal structure. We examined the histological structure of cement glands and explored the variations in cement protein homologs of 12 barnacle species with different attachment habitats and base materials.ResultsCement gland cells in the rocky shore barnacles Tetraclita japonica formosana and Amphibalanus amphitrite are eosinophilic, while others are basophilic. Transcriptome analyses recovered CP homologs from all species except the scleractinian coral barnacle Galkinia sp. A phylogenomic analysis based on sequences of CP homologs did not reflect a clear phylogenetic pattern in attachment substrates. In some species, certain CPs have a remarkable number of paralogous sequences, suggesting that major duplication events occurred in CP genes. The examined CPs across taxa show consistent bias toward particular sets of amino acid. However, the predicted isoelectric point (pI) and hydropathy are highly divergent. In some species, conserved regions are highly repetitive.ConclusionsInstead of developing specific cement proteins for different attachment substrata, barnacles attached to different substrata rely on a highly duplicated cementation genetic toolkit to generate paralogous CP sequences with diverse chemical and biochemical properties. This general CP cocktail might be the key genetic feature enabling barnacles to adapt to a wide variety of substrata.
Highlights
Barnacles are sessile crustaceans that attach to underwater surfaces using barnacle cement proteins
The Cement glands (CGs) of the acorn barnacles A. amphitrite, T. j. formosana, C. testudinaria, C. malayensis and M. ajax are located in the basal mantle region and closely associated with the ovarian tissue
CG could be identified by the presence of unicellular cement gland cells (CGCs), which are structurally distinct from the ovarian follicle cells
Summary
Barnacles are sessile crustaceans that attach to underwater surfaces using barnacle cement proteins. We tested the hypothesis that the cement protein (CP) composition and chemical properties of different species vary according to the attachment substrate and/or the basal structure. We examined the histological structure of cement glands and explored the variations in cement protein homologs of 12 barnacle species with different attachment habitats and base materials. Cementation of sessile organisms typically involves three major components: (1) the surface of the sessile organism attaching to the substratum, (2) bioadhesive substances and (3) the substratum to which organisms are attaching. Bioadhesive substances are the key components responsible for gluing an organism’s attachment surface to a substratum. It remains unclear whether or to what extent the evolution of bioadhesive substances in these sessile organisms are influenced by the proximal bottom structure and/or the substratum materials
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