The expression pattern of FHL2 during mouse molar development.

Four and a half LIM domains 2 (FHL2) functions as a transcriptional co-activator or co-repressor in a cell-type-specific manner. As a positive regulator, FHL2 plays an important role in osteoblast differentiation and bone formation. Our previous study showed that FHL2 was expressed in odontoblasts in mature human teeth under normal and pathological conditions. The purpose of this study was to investigate the spatial-temporal expression patterns of FHL2 at different stages of mouse molar development by immunohistochemistry. Our results showed that at the bud and cap stage, FHL2 was expressed both in enamel organ and the underlying mesenchyme. At the early bell stage, FHL2 appeared in the inner and outer enamel epithelium, stratum intermedium and the secondary enamel knot. Positive staining gradually converged at the cusps of dental papilla. At the late bell stage, FHL2 was expressed in the terminal differentiated ameloblasts and odontoblasts and stratum intermedium. At the postnatal day, FHL2 was detected in the secretory and mature ameloblasts and odontoblasts and mature enamel, and gradually appeared at Hertwig's epithelial root sheath and periodontal tissues. The spatial-temporal expression patterns of FHL2 from the bud stage to the postnatal day (13.5) suggested that during tooth development, FHL2 might play an important role in ameloblast and odontoblast differentiation, secretion of enamel and dentin matrix, mineralization of enamel, molar crown morphogenesis, as well as root formation.