IMMUNOCYTOCHEMICAL INVESTIGATION OF THE RAT CEMENTOBLAST PHENOTYPE

Recent studies have suggested that cementoblasts may be derived from o steoblast progenitor cells, although the cementoblast phenotype has no t been extensively characterized. This immunocytochemical study was ca rried out to investigate the expression by rat cementoblasts of a numb er of proteins which are characteristic of the osteoblast phenotype. P araffin sections from developing rat tooth germs and from fully formed adult rat teeth with surrounding tissues, were incubated with antibod ies to type I & III collagen, osteocalcin, transforming growth factor beta (TGEbeta), and insulin-like growth factor 1 (IGF1). Frozen sectio ns and unfixed resin-embedded sections were stained for alkaline phosp hatase activity. Cementum and bone matrix were strongly positive for t ype I collagen, although there was only weak staining for type III col lagen. Cementum was also positive for osteocalcin, which was particula rly strong in the matrix of acellular cementum. Most osteoblasts and c ementoblasts of the cellular cementum showed intense staining for TGFb eta and IGF1, although some cementocytes and osteocytes were negativel y stained. The osteoblast- specific anti-E11 mAb reacted strongly with cementoblasts and newly formed cementocytes in the cellular cementum. Cells associated with acellular cementum did not express TGFbeta, IGF 1 or stain positively with anti-E11 antibody at any time during root d evelopment. Cementoblasts were weakly or negatively stained for alkali ne phosphatase in contrast to the osteoblasts examined, which may refl ect the low level of synthetic activity in cementoblasts. These result s demonstrate that osteoblasts and cementoblasts of cellular cementum share many phenotypic characteristics, and also suggest that there may be phenotypic differences between cementoblasts associated with cellu lar and acellular cementum.