EXPRESSION PATTERNS OF BONE-RELATED PROTEINS DURING OSTEOBLASTIC DIFFERENTIATION IN MC3T3-E1 CELLS

Bone formation involves several tightly regulated gene expression patt erns of bone-related proteins. To determine the expression patterns of bone-related proteins during the MC3T3-E1 osteoblast-like cell differ entiation, we used Northern blotting, enzymatic assay, and histochemis try. We found that the expression patterns of bone-related proteins we re regulated in a temporal manner during the successive developmental stages including proliferation (days 4-10), bone matrix formation/matu ration (days 10-16), and mineralization stages (days 16-30). During th e proliferation period (days 4-10), the expression of cell-cycle relat ed genes such as histone H3 and H4, and ribosomal protein S6 was high. During the bone matrix formation/maturation period (days 10-16), type I collagen expression and biosynthesis, fibronectin, TGF-beta 1 and o steonectin expressions were high and maximal around day 16. During thi s maturation period, we found that the expression patterns of bone mat rix proteins were two types: one is the expression pattern of type I c ollagen and TGF-beta 1, which was higher in the maturation period than that in both the proliferation and mineralization periods. The other is the expression pattern of fibronectin and osteonectin, which was hi gher in the maturation and mineralization periods than in the prolifer ation period. Alkaline phosphatase activity was high during the early matrix formation/maturation period (day 10) and was followed by a decr ease to a level still significantly above the baseline level seen at d ay 4. During the mineralization period (days 16-30), the number of nod ules and the expression of osteocalcin were high. Osteocalcin gene exp ression was increased up to 28 days. Our results show that the express ion patterns of bone-related proteins are temporally regulated during the MC3T3-E1 cell differentiation and their regulations are unique com pared with other systems. Thus, this cell line provides a useful in vi tro system to study the developmental regulation of bone-related prote ins in relation to the different stages during the osteoblast differen tiation. (C) 1996 Wiley-Liss, Inc.