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Is the Adhesive Material Secreted by Sea Urchin Tube Feet Speciesspecific?

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Is the Adhesive Material Secreted by Sea Urchin Tube Feet Speciesspecific? JOURNAL OF MORPHOLOGY 273:40–48 (2012) Is the Adhesive Material Secreted by Sea Urchin Tube Feet Species-Specific? Romana Santos1,2* and Patrick Flammang1* 1Universite´ de Mons—UMONS, Acade´mie Universitaire Wallonie Bruxelles, Laboratoire de Biologie Marine, Mons 7000, Belgium 2Unidade de Investigac¸a˜o em Cieˆncias Orais e Biome´dicas, Faculdade de Medicina Denta´ria, Universidade de Lis- boa, Cidade Universita´ria, Lisboa 1649-003, Portugal ABSTRACT Sea urchin adoral tube feet are highly spe- retract, whereas the disk makes contact with and cialized organs that have evolved to provide efficient attaches to the substratum (Flammang, 1996; San- attachment to the substratum. They consist of a disk and tos et al., 2009a). The disk epidermis encloses a a stem that together form a functional unit. Tube foot duo-gland adhesive system, which comprises two disk tenacity (adhesive force per unit area) and stem me- types of secretory cells releasing adhesive and chanical properties (e.g., stiffness) vary between species but are apparently not correlated with sea urchin taxa or deadhesive secretions (Hermans, 1983; Flammang habitats. Moreover, ultrastructural studies of sea urchin and Jangoux, 1993; Flammang, 1996). Adhesive disk epidermis pointed out differences in the internal or- secretions are delivered through the disk cuticle to ganization of the adhesive secretory granules among spe- the tube foot–substratum interface where they cies. This prompted us to look for interspecific variability form a thin film that fastens the disk to the sur- in the composition of echinoid adhesive secretions, which face (Santos et al., 2009a). Although strong, this could explain the observed variability in adhesive granule adhesion is temporary and sea urchins can detach ultrastructure and disk tenacity. Antisera raised against their tube feet from the substratum through the the footprint material of Sphaerechinus granularis (S. release of a deadhesive secretion (Flammang et al., granularis) were first used to locate the origin of adhesive 2005). After detachment the adhesive material footprint constituents in tube feet by taking advantage of the polyclonal character of the generated antibodies. Im- remains strongly attached to the substratum as a munohistochemical assays showed that the antibodies footprint (Flammang and Jangoux, 1993; Santos specifically labeled the adhesive secretory cells of the disk et al., 2009a). epidermis in the tube feet of S. granularis. The antibodies It has often been reported that regular echinoid were then used on tube foot histological sections from species belonging to different taxa and inhabiting seven other sea urchin species to shed some light on the different environments possess different types of variability of their adhesive substances by looking for tube feet and that a general correlation might exist antibody cross-reactivity. Surprisingly, no labeling was between the degree of development of these tube observed in any of the species tested. These results indi- feet and the maximum environmental energy that a cate that unlike the adhesive secretions of asteroids, species can withstand (Sharp and Gray, 1962; those of echinoids do not share common epitopes on their constituents and thus would be ‘‘species-specific.’’ In sea urchins, variations in the composition of adhesive secre- Contract grant sponsor: R.S. is an Associate Researcher of Cieˆn- tions could therefore explain interspecific differences cia 2008 Program supported by the Portuguese Foundation for Sci- in disk tenacity and in adhesive granule ultrastructure. ence and Technology; P.F. is Senior Research Associate of the Fund J. Morphol. 273:40–48, 2012. Ó 2011 Wiley Periodicals, Inc. for Scientific Research of Belgium (F.R.S.-FNRS); Contract grant sponsor: Fund for Scientific Research of Belgium (F.R.S.-FNRS); KEY WORDS: temporary adhesion; tube feet; adhesive Contract grant number: FRFC 2.4532.07 and COST Action TD0906 secretions; antibody cross-reactivity; Echinoidea (http://www.cost-bioadhesives.org/). *Correspondence to: R. Santos, Unidade de Investigac¸a˜oemCieˆn- cias Orais e Biome´dicas, Faculdade de Medicina Denta´ria, Universi- dade de Lisboa, Cidade Universita´ria, Lisboa 1649-003, Portugal. E-mail: [email protected] or P. Flammang, Universite´ de INTRODUCTION Mons—UMONS, Acade´mie Universitaire Wallonie Bruxelles, Labo- ratoire de Biologie Marine, 20 Place du Parc, Mons 7000, Belgium. Being exclusively benthic animals and inhabit- E-mail: patrick.fl[email protected]. ing areas with variable hydrodynamic conditions, sea urchins have developed specialized organs, the Received 25 May 2011; Revised 16 June 2011; adoral tube feet, to provide efficient attachment to Accepted 19 June 2011 the substratum. Tube feet are made up of a stem Published online 15 August 2011 in and a disk that together form a functional unit; Wiley Online Library (wileyonlinelibrary.com) the stem allows the tube foot to lengthen, flex, and DOI: 10.1002/jmor.11004 Ó 2011 WILEY PERIODICALS, INC. IMMUNOHISTOCHEMICAL STUDY OF ECHINOID TUBE FEET 41 Smith, 1978). However, recent studies failed to dem- allowed to walk across and/or attach to the bottom of clean onstrate a clear relationship between tube foot me- glass Petri dishes placed inside small aquaria filled with artifi- cial seawater. Animals were repeatedly detached to induce chanical properties, such as disk tenacity or stem novel attachments and thus obtain more footprints. Then, the stiffness, and sea urchin habitat (Santos and Flam- Petri dishes were thoroughly washed with milliQ water and mang, 2005, 2006, 2008). Yet, disk tenacity meas- placed in a freeze-dryer. Lyophilized footprint material was ured on standard substrata (i.e., glass or poly- then scrapped off using a clean razor blade and stored at 2 8 l methyl-methacrylate (PMMA)) varied by up to a 20 C. This method allowed the collection of 150 g of a red- brown powder per Petri dish. factor of three among different sea urchin species (Santos and Flammang, 2006, 2008). Moreover, at the ultrastructural level, significant interspecific Antisera Production and Characterization variations were found in the internal organization of the adhesive secretory granules suggesting that Polyclonal antisera were raised in two female rabbits (R5 and R6) against the whole footprint material. The immunization there might be molecular differences in the composi- schedule was as follows: About 1 mg of footprint material was tion of their adhesive secretions (Santos and Flam- suspended in 0.5 ml of 0.9% NaCl and emulsified with an equal mang, 2006). This hypothesis has been recently cor- volume of complete Freund’s adjuvant (Difco, Detroit, MI). The roborated by the study of the protein fraction of the rabbits were then injected subcutaneously at several sites in footprints from Paracentrotus lividus (P. lividus; the back with 1 ml of the emulsion. Four boosts were prepared identically but with incomplete Freund’s adjuvant and adminis- Santos et al., 2009b). De novo-generated peptide tered, 14, 28, 56, and 84 d after the first injection. Antisera sequences were obtained for 5 of the 13 proteins were harvested four times: 10 d after the second boost (AS1), 10 constituting the footprint material, but these d after the third boost (AS2), and 17 and 31 d after the fourth sequences showed no homology with the available boost (AS3 and AS4, respectively). Unfortunately, rabbit R5 had to be sacrificed 4 d after the first bleeding due to back problems; databases, including the predicted protein database therefore, for this rabbit, only two antisera are available (AS1 from the genome of the sea urchin Strongylocentro- and AS2). Preimmune sera were also obtained by bleeding the tus purpuratus (Sea Urchin Genome Sequencing rabbits just before the first injection of footprint material. Anti- Consortium, 2006; Santos et al., 2009b). sera production was performed as a service (Laboratoire d’Hor- Therefore, the aim of this study was to shed some monologie, Marloie, Belgium) and complied with all legal requirements. light on the molecular variability of the adhesive The different antisera and preimmune sera were tested for material in regular echinoids. The exact biochemical specific footprint-binding activity using an enzymatic immuno- composition of the adhesive secretions is not known assay. Footprints were collected on clean glass slides as for any sea urchin species, although a partial char- described above. Their presence was checked by soaking a few slides for 1 min in a 0.05% Crystal Violet solution in distilled acterization of the footprint material has recently water (Flammang et al., 1994). The remaining slides were pre- been reported in the species P. lividus (Santos et al., incubated for 30 min in 10% normal swine serum (Dako, 2009b). To bypass the complete characterization of Golstrup, Denmark) in phosphate-buffered saline (PBS, pH 7.4) echinoid adhesives, a comparative immunohisto- to block nonspecific antigenic sites. Antisera and preimmune chemical approach was used. Polyclonal antibodies sera diluted, respectively, 1:500 and 1:100 in PBS containing 1% Tween-20 and 1% bovine serum albumin (BSA) (PBS- were raised against the footprint material of one Tween-BSA1), were then applied overnight at 48C. After several species, Sphaerechinus granularis (S. granularis) washes in PBS-Tween-BSA1, the slides were incubated for 30 and used to evaluate differences in the composition min with secondary antibodies (swine antirabbit IgG; Dako, of the contents of tube foot adhesive cells by looking Golstrup, Denmark) at a dilution of 1:100 in PBS-Tween-BSA1, followed by an incubation of 30 min with the peroxidase–anti- for antibody cross-reactivity on histological sections peroxidase (PAP; Dako, Golstrup, Denmark) complex also made from the tube feet of seven regular sea urchin diluted 1:100 in PBS-Tween-BSA1. After the final rinses in species belonging to three orders and five families of PBS, immunoreactivity was visualized using 3,30-diaminobenzi- the Class Echinoidea. This approach was chosen, dine tetra hydrochloride (SIGMA FASTTM DAB with Metal because it was previously used successfully to com- Enhancer Tablets, Sigma, St.
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