Calcification of Cartilage from the Lamprey Petromyzon marinus (L.) in vitro

Abstract

Adult and larval lamprey cartilage, normally unmineralized, was cultured in a medium meta‐stable for hydroxyapatite for periods of up to 12 days at 20, 30 or 37°C. Histochemical analysis revealed a temperature‐dependent increase over time in calcium phosphate incorporation into the extracellular matrix (ECM) of adult cartilage concomitant with the incorporation of calcium as detected by gravimetric and radioisotopic methods. Ultrastructural analysis revealed the presence of ECM dense bodies (40 nm average) containing crystalline material which increased in number with increased mineral incorporation but were absent from control cartilage. Additionally, electron‐dense particles (15–20 nm) found in close association with the ECM fibrils in some regions of mineralized cartilage may represent sites of amorphous calcium phosphate. Larval cartilage incorporated much less calcium, less uniformly over time than did adult cartilage. Histochemical and ultrastructural analysis revealed that calcium had accumulated in the chondrocytes instead of the ECM and this proved detrimental, leading to the death of the cells. The discovery that adult lamprey cartilage calcifies in vitro under appropriate conditions, suggests that petromyzonids, or their direct agnathan ancestors, may have possessed mineralized skeletons and that this ability is ‘repressed’ in extant lampreys owing primarily to the environment they inhabit.

Origin and early evolution of vertebrate skeletonization

“…Rather, the earliest representation of the vertebrate "skeletal system" relates entirely to feeding and respiration. To an extent, this conflates skeletonization with calcification, but the distinction between the two is hard to draw (e.g., Langille and Hall, 1993;Meunier and Huysseune, 1992) since they are interdependent, as can be evidenced by the fact that in most jawed vertebrates development of the embryonic endoskeleton proceeds without calcification until much of the structure has been established. Until the origin of the dermoskeleton, to which all the existing hypotheses relate, the evolution of skeletonization within the vertebrate lineage was all endoskeletal, and almost entirely splanchnocranial.…”

“…The controversy surrounding conodont and thelodont oral skeletal elements notwithstanding, lampreys are the earliest members of the vertebrate lineage to exhibit evidence of endoskeletal calcification (Langille and Hall, 1993), in both the neurocranium and splanchocranium, although there is little more than circumstantial evidence to indicate that this extends beyond in vitro conditions (e.g., Bardack and Zangerl, 1971). There is equivocal evidence of a mineralized endoskeleton among the heterostracomorphs: globular calcified cartilage is found in association with one of the heterostracomorphs, Eriptychius ( Fig.…”

“…Lampreys afford the earliest evidence of skeletal calcification within the vertebrate lineage (Langille and Hall, 1993).…”

Growth and patterning in the conodont skeleton

“…Agnathan statoliths are composed from an amorphous (polyhydroxyl) calcium phosphate, which is highly unstable and dissolves in a solution of pH 8 or less (R. W. Gauldie, personal communication). Lamprey biomineralization is similarly restricted to the formation of statoliths, although under the right conditions (in vivo or in vitro) lampreys are capable of skeletal biomineralization, in particular, calci¢-cation of cartilage (Langille 1987;Langille & Hall 1993;Bardack & Zangerl 1971).…”

Comparative equilibrium mechanical properties of bovine and lamprey cartilaginous tissues

“…The mean E of aged pericardial cartilage was found to be statistically larger than the mean E of young and aged annular cartilage, young pericardial cartilage, as well as bovine auricular cartilage tested in tension and compression. Since lamprey cartilage has demonstrated the ability to calcify in vitro (Langille and Hall, 1993), the 'crisp' consistency of aged lamprey pericardial cartilage suggested a possible deposition of calcium within the cartilage ECM, within the chondrocytes or, possibly, within the inter-fibrillar spaces of perichondrial collagen fibers. However, staining with alizarin red was inconclusive; young and aged pericardial cartilages gave staining patterns that were virtually identical (both with and without EDTA treatment).…”