DETECTION OF GELATINASE-B EXPRESSION REVEALS OSTEOCLASTIC BONE-RESORPTION AS A FEATURE OF EARLY CALVARIAL BONE-DEVELOPMENT

Gelatinase B is a matrix metalloproteinase (MMP-9) produced by osteocl asts involved in bone resorption. Bone modeling, of which resorption i s an integral part, is particularly evident in the intramembranous bon es of the craniofacial region, To determine the role of osteoclasts in developing intramembranous bones we localized osteoclasts in calvaria e from mice aged between embryonic day 16 and postnatal day 6, using g elatinase B and tartrate-resistant acid phosphatase activity (TRAP) as osteoclast markers, Through a combined approach of in situ hybridizat ion and enzyme histochemistry, phenotypic differences between osteocla sts associated with calvarial bone were noted, Some cells expressed ge latinase B mRNA but were TRAP negative, whereas others demonstrated an overlap in enzyme profile exhibiting both TRAP activity and expressin g gelatinase B mRNA, During more advanced development, most osteoclast s exhibited TRAP activity but did not express gelatinase B mRNA. The d istribution of these cells differed, TRAP positive cells being detecte d in a widespread pattern at all ages, while gelatinase B transcripts were increasingly concentrated in areas of new and rapid bone growth, notably around the sutures. We propose the use of gelatinase B as an o steoclastic marker in the developing mouse. We conclude that gelatinas e B mag have a keg role during early bone formation, the regulation of bone modeling, and perhaps in the maintenance of suture width, (C) 19 97 by Elsevier Science Inc. All rights reserved.