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Murine Metapodophalangeal Sesamoid Bone Mineralization

其他書名	A Light and Electron Microscopy Study
出版	Kent State University, 2007
URL	http://books.google.com.hk/books?id=2eBGAQAACAAJ&hl=&source=gbs_api

註釋In calcifying cartilage, early bone, and dentin, mineral crystal nucleation and growth are reported to occur first in matrix vesicles and then proceed within the extracellular organic matrices of these tissues (Lowenstam and Weiner, On Biomineralization, Oxford University Press, 1989). In normally mineralizing turkey leg tendons, type I collagen independently initiates mineral formation in areas isolated from matrix vesicles. In this tissue, collagen-mediated nucleation succeeds vesicle-mediated nucleation (Landis and Silver, Comp. Biochem. Physiol. A, 133:1135-1157, 2002). Sesamoid bones of vertebrates are unique in their size and close association with tendon, providing an opportunity to examine possible vesicle- and/or collagen-mediated mineralization in relation to bone and tendon. This study established a maturation timeline of murine metapodophalangeal sesamoid bones and investigated potential matrix vesicle presence and vesicle/collagen/mineral interactions in this tissue. Sesamoid bones, located between the metapodials and proximal phalanges, were examined in one- to six-week-old postnatal normal CD-1 mice through use of radiography, histology, and whole mount staining. These combined data provided the means to define the general morphology and development of the sesamoids, their association with tendon, collagen and proteoglycan presence, and surrounding tissue maturational changes. Murine metapodophalangeal sesamoid bones began mineralization as early as one week of age. The calcification of the epiphyseal plates of the metapodia and proximal phalanges began in advance of sesamoid mineral formation. Mineralization occurred first in the one-week metacarpophalangeal joint of the second digit as a mineral nodule within the cartilaginous core of the lateral-most sesamoid. Complete calcification was obtained between three and four weeks, resulting in a large, oblate sesamoid. Ossification of these small bones occurred before the epiphyseal plates were fully fused. In the TEM analysis of two-week metacarpophalangeal lateral sesamoids, extracellular matrix vesicles were found in small numbers and were not believed to be involved with mineral formation in this bone. In addition, the perpendicular orientation of the collagen fibers in the tissues examined was unexpected. Therefore, the roles of matrix vesicles and type I collagen in the mineralizing sesamoid bones were determined to be inconclusive. It is assumed that extensive proteoglycan networks and type II collagen fibers initiate mineralization in murine metapodophalangeal sesamoid bones.