CD44 EXPRESSION IN FETAL-RAT BONE - IN-VIVO AND IN-VITRO ANALYSIS

Knowledge of the expression pattern of the cell surface glycoprotein C D44 in the development and differentiation of bone is limited. We inve stigated CD44 expression (a) in bone sections of 21-day-old fetal rat calvaria (RC), metatarsals, and tibiae, (b) in primary cultures of Re cells undergoing differentiation in vitro, and (c) in three rat osteos arcoma cell lines: ROS 17/2.8, UMR 106.01, and UMR 106.06. By immunocy tochemistry, Western, Northern, and reverse transcription polymerase c hain reaction analyses, we found that osteoblastic cells express the ' 'hematopoietic'' or ''standard'' CD44 (CD44s) isoform. Osteoblastic ce lls in vivo and in vitro stained at all detectable stages of different iation, but intercellular heterogeneity of CD44s staining was evident, with lesser staining in preosteoblastic cells and greater staining in mature osteoblasts and osteocytes. As cells in RC cultures differenti ated and formed bone in vitro, CD44s mRNA and protein levels as measur ed on immunoblots were invariant. All three osteosarcoma cell lines ex pressed CD44s mRNA and protein. The synthetic glucocorticoid dexametha sone, which stimulates osteogenesis in RC cells in vitro and regulates a number of osteoblast-associated genes, had no apparent effect on ei ther CD44s protein or mRNA levels. The widespread presence of CD44s in osteoblastic cells at various maturational stages suggests that furth er analyses will be required to determine what role CD44s may play in osteogenesis and in bone tissue organization. (C) 1996 Academic Press, Inc.