title: Ultrastructural, material and crystallographic description of endophytic masses - A possible damage response in shark and ray tessellated calcified cartilage.
abstract: The cartilaginous endoskeletons of elasmobranchs (sharks and rays) are reinforced superficially by minute, mineralized tiles, called tesserae. Unlike the bony skeletons of other vertebrates, elasmobranch skeletons have limited healing capability and their tissues' mechanisms for avoiding damage or managing it when it does occur are largely unknown. Here we describe an aberrant type of mineralized elasmobranch skeletal tissue called endophytic masses (EPMs), which grow into the uncalcified cartilage of the skeleton, but exhibit a strikingly different morphology compared to tesserae and other elasmobranch calcified tissues. We use materials and biological tissue characterization techniques, including computed tomography, electron and light microscopy, X-ray and Raman spectroscopy and histology to characterize the morphology, ultrastructure and chemical composition of tesserae-associated EPMs in different elasmobranch species. EPMs appear to develop between and in intimate association with tesserae, but lack the lines of periodic growth and varying mineral density characteristic of tesserae. EPMs are mineral-dominated (high mineral and low organic content), comprised of birefringent bundles of large calcium phosphate crystals (likely brushite) aligned end to end in long strings. Both tesserae and EPMs appear to develop in a type-2 collagen-based matrix, but in contrast to tesserae, all chondrocytes embedded or in contact with EPMs are dead and mineralized. The differences outlined between EPMs and tesserae demonstrate them to be distinct tissues. We discuss several possible reasons for EPM development, including tissue reinforcement, repair, and disruptions of mineralization processes, within the context of elasmobranch skeletal biology as well as damage responses of other vertebrate mineralized tissues.
authors.affiliation: Department Biomaterials, Max Planck Institute of Colloids & Interfaces, Potsdam, Germany. Electronic address: ronald.seidel@mpikg.mpg.de.
authors.forename: Ronald
authors.initials: R
authors.lastname: Seidel
authors.affiliation: Division of Clinical and Functional Anatomy, Medical University of Innsbruck, Innsbruck, Austria.
authors.forename: Michael
authors.initials: M
authors.lastname: Blumer
authors.affiliation: Julius Wolff Institute, Charité - Universitätsmedizin Berlin, Germany; Department for Restorative and Preventive Dentistry, Charité - Universitätsmedizin Berlin, Germany.
authors.forename: Paul
authors.initials: P
authors.lastname: Zaslansky
authors.affiliation: Department Visualization and Data Analysis, Zuse Institute Berlin, Germany.
authors.forename: David
authors.initials: D
authors.lastname: Knötel
authors.affiliation: Department of Biology, The University of Tampa, 401 W. Kennedy Blvd, Tampa, FL, USA.
authors.forename: Daniel R
authors.initials: DR
authors.lastname: Huber
authors.affiliation: Wyss Institute for Biologically Inspired Engineering, Harvard University, Cambridge, MA, USA.
authors.forename: James C
authors.initials: JC
authors.lastname: Weaver
authors.affiliation: Department Biomaterials, Max Planck Institute of Colloids & Interfaces, Potsdam, Germany.
authors.forename: Peter
authors.initials: P
authors.lastname: Fratzl
authors.affiliation: Department Biomaterials, Max Planck Institute of Colloids & Interfaces, Potsdam, Germany; Department of Chemical and Biological Engineering, University of Ottawa, Canada.
authors.forename: Sidney
authors.initials: S
authors.lastname: Omelon
authors.affiliation: Department Biomaterials, Max Planck Institute of Colloids & Interfaces, Potsdam, Germany.
authors.forename: Luca
authors.initials: L
authors.lastname: Bertinetti
authors.affiliation: Department Biomaterials, Max Planck Institute of Colloids & Interfaces, Potsdam, Germany.
authors.forename: Mason N
authors.initials: MN
authors.lastname: Dean
mesh_terms: D000818:Animals; D002113:Calcification, Physiologic; D002356:Cartilage / Q000648:ultrastructure*; D003461:Crystallography; D008903:Minerals / Q000032:analysis; D012754:Sharks; D012863:Skeleton / Q000648:ultrastructure; D013057:Spectrum Analysis; D014945:Wound Healing
chemical_list: D008903:Minerals
keywords: Callus; Elasmobranch cartilage; Mineralization; Skeletal damage; Skeleton; Tesserae