Ea. Cowles et al., MINERALIZATION AND THE EXPRESSION OF MATRIX PROTEINS DURING IN-VIVO BONE-DEVELOPMENT, Calcified tissue international, 62(1), 1998, pp. 74-82
The in vivo expression of fibronectin, type I collagen, and several no
n-collagenous proteins was correlated with the development of bone in
fetal and early neonatal rat calvariae. Fibronectin was the earliest m
atrix protein expressed in calvariae: with a peak expression in fetal
16- and 17-day (d) bones. Fibronectin expression coincided with the co
ndensation of preosteoblasts prior to calcification and decreased once
bone mineralization commenced. The expression of type I collagen, ost
eonectin, bone sialoprotein, and all;aline phosphatase mRNAs was found
at 17 d, The increase in type I collagen mRNA levels was correlated w
ith a 3.5-fold increase in calcium deposition at 19-20 d. Bone sialopr
otein and alkaline phosphatase peaked on fetal 21 d while osteonectin
remained at a low level and was localized to the osteoblast layer and
the osteocyte lacunae. Osteopontin mRNA levels increased rapidly in ne
onatal calvariae, After birth, osteonectin and fibronectin were mainly
associated with blood vessels, Thus, fibronectin is one of the earlie
st matrix proteins expressed in calvariae and is rapidly followed by t
ype I collagen, bone sialoprotein, and alkaline phosphatase. Osteocalc
in, osteonectin, and osteopontin mRNAs have similar patterns of expres
sion in the developing fetal calvaria, and their synthesis coincided w
ith mineralization.