| Several in vitro model systems have been developed to examine and characterize the cellular and molecular events that underlie osteogenesis. The chick periosteal osteogenesis (CPO) model has several unique features, including the ability to mimic the anatomical and biochemical events that occur during osteogenesis in vivo, that can facilitate the examination of discrete temporal phases of osteogenesis such as differentiation, matrix formation and mineralization. However, the molecular mechanisms governing avian osteogenesis are largely unknown. The aim of the studies presented here, therefore, was to determine the spatial and temporal expression profiles of key genes involved in bone formation including a master regulator of osteogenesis, core binding factor alpha-1 (Cbfa-1). Using Northern hybridization, semi-quantitative polymerase chain reaction (PCR) analysis and in situ hybridization, the mRNA expression profiles of a panel of bone-associated genes including osteopontin, bone sialoprotein, alkaline phosphatase, type 1 collagen, osteocalcin, bone morphogenetic protein (BMP)-7 and BMP type 2 receptor were examined during discrete phases of osteogenesis and in distinct regions of the developing bone. In addition, the mRNA expression of Cbfa-1 and Ets-family transcription factor members was also investigated to provide insights into the molecular mechanisms that regulate avian bone formation. Taken together, these studies provide a gene expression profile for avian osteogenesis and provide a molecular perspective from which perturbation of osteogenesis by various biological and pharmacological agents can be evaluated. Moreover the results of these studies demonstrate that molecular events within the developing osteoid are highly organized and compartmentalized to specific cell layers around the central area of bone formation. |
