Osteoadherin is a cell binding keratan sulfate proteoglycan which was recen
tly isolated from mineralized bovine bone and subsequently cloned and seque
nced. For studies of osteoadherin expression in rat tissues we isolated and
sequenced a 1.3-kbp partial cDNA covering most of the coding region using
a rat calvaria cDNA library. The most 5' end of the cDNA was obtained by re
verse transcription PCR from the bone total RNA preparation. The deduced, t
ranslated protein sequence containing 423 amino acid residues shows high se
quence identity to mouse, bovine and human osteoadherin except in the very
acidic C-terminal region. However, the rat counterpart showed a similarly h
igh content of acidic amino acid residues. Ribonuclease protection assay sh
owed osteoadherin mRNA to be expressed in femoral bone and calvaria tissues
, while no expression was detected in cartilage, tendon or liver. Using ver
y sensitive nested RT-PCR, however, message was detected in femoral head, r
ib, tendon and bone marrow total RNA preparations. An antiserum specific fo
r the rat C-terminal region of osteoadherin was generated and used for stud
ies of protein distribution by immunohistochemistry during femoral head dev
elopment. Osteoadherin was primarily present in bone trabeculae and no stai
ning was seen in cartilage. In situ hybridization showed the strongest expr
ession in osteoblasts close to the cartilage/bone interface of the growth p
late and lower expression in diaphyseal osteoblasts. On maturation of the f
emoral head on day 60 some expression was detected immediately below the fo
rming articular cartilage. Our data indicated that osteoadherin is primaril
y expressed by osteoblasts and might have a role in regulation of mineraliz
ation. (C) 1999 Published by Elsevier Science B.V./International Society of
Matrix Biology. All rights reserved.