Localization of alkaline phosphatase and osteopontin during matrix mineralization in the developing cartilage of coccygeal vertebrae

We observed the manner in which alkaline phosphatase (ALPase) and osteopont in were localized in the cartilage and intramembranous bone of coccygeal ve rtebrae during matrix mineralization, shedding considerable light on the ma nner in which they develop. In the cartilage matrix of coccygeal vertebrae, we observed the localization of ALPase activity in the boundary of the pro liferative and the hypertrophic zones. Granular nodules of mineralization w ere consistently found in the boundary of both zones, and increased in size when close to the hypertrophic zone. While osteopontin was rarely present in the early stages of mineralization, its localization along the margins o f mineralized matrices in the hypertrophic zone was prominent, In contrast to cartilage, mineralized nodules in the intramembranous bone in the mid-po rtion of the vertebra displayed osteopontin-immuorecactivity, indicating it s early synthesis and subsequent accumulation to early-stage mineralized no dules, When blood vessels, accompanied by osteoblastic and osteoclastic cel l populations, invaded the cartilage, osteopontin was localized in the lowe r region of the hypertrophic zone, despite its maintaining the localization of ALPase and early-stage mineralization, Thus, our investigation demonstr ated ALPase activity consistent with early-stage mineralization in the cart ilage matrix. However, the fact that osteopontin-localization could not be pinpointed might account for its multifunctionality as concerns both the re gulation of mineralization and the attachment of migrating osteogenic and o steoclastic cells to the mineralized matrix.