title: Globuli ossei in the long limb bones of Pleurodeles waltl (Amphibia, Urodela, Salamandridae).
abstract: To date, little is known about the structure of the cells and the fibrillar matrix of the globuli ossei, globular structures showing histochemical properties of an osseous tissue, sometimes found in the resorption front of the hypertrophied cartilage in many tetrapods, and easily observed in the long bones of the Urodele Pleurodeles waltl. Here, we present the results obtained from the appendicular long bones of metamorphosed juveniles and subadults using histological and histochemical methods and transmission electron microscopy. The distal part of the cone-shaped cartilage contains a heterogeneous cell population composed of the typical "light" hypertrophic chondrocytes and scarce "dark" hypertrophic chondrocytes. The "dark" chondrocytes display ultrastructural characteristics suggesting that they probably undergo degeneration through chondroptosis. However, in the hypertrophic, calcified cartilage close to the erosion front by the marrow, several noninvaded chondrocytic lacunae retained cells that do not show any morphological characteristics of degeneration and that cannot be identified as regular chondrocytes or osteocytes. These modified chondrocytes that have lost their regular morphology, appear to be active in the terminal cartilage and synthesize collagen fibrils of a peculiar diameter intermediate between the Type I collagen found in bone and the Type II collagen characteristic of cartilage. It is suggested that the local occurrence of globuli ossei is linked to a low rate of longitudinal growth as is the case in the long bones of postmetamorphic urodeles.
authors.affiliation: Sorbonne Universités, UPMC Univ Paris 06, UMR 7193, Institut des Sciences de la Terre Paris (ISTeP), Equipe Biominéralisations et Environnements Sédimentaires, F-75005, Paris, France; CNRS, UMR 7193, Institut des Sciences de la Terre Paris (ISTeP), F-75005, Paris, France.
authors.forename: Alexandra
authors.initials: A
authors.lastname: Quilhac
authors.forename: Armand
authors.initials: A
authors.lastname: de Ricqlès
authors.forename: Hayat
authors.initials: H
authors.lastname: Lamrous
authors.forename: Louise
authors.initials: L
authors.lastname: Zylberberg
mesh_terms: D000818:Animals; D001846:Bone Development; D001842:Bone and Bones / Q000033:anatomy & histology*; D002454:Cell Differentiation; D019902:Chondrocytes / Q000648:ultrastructure*; D005109:Extracellular Matrix; D005121:Extremities / Q000033:anatomy & histology; D006132:Growth Plate / Q000648:ultrastructure*; D051457:Hyaline Cartilage / Q000648:ultrastructure*; D006984:Hypertrophy; D046529:Microscopy, Electron, Transmission; D010011:Osteocytes / Q000648:ultrastructure*; D010999:Pleurodeles / Q000033:anatomy & histology*
keywords: chondroptosis; dark chondrocytes; endochondral ossification; limb; ultrastructure; urodeles