Cellular retinoic acid binding protein in the periodontal ligament

As retinoic acid is an important signaling molecule during embryological development. Since periodontal tissues are thought to have fetal-like properties, the present study was to determine the presence and distribution of cellular retinoic acid-binding protein I(CRABPI) in the periodontal tissues of the rat. Following demineralization, wax sections of the molar teeth of four adult male rats were cut in a plane parallel to the molar tooth row. Five representative sections from each jaw were then processed and stained to reveal the presence of CRABP. This protein was identified by immunochemistry utilizing an affinity-purified rabbit polyclonal antibody. The IgG antibody was used at a dilution of 1 microgram ml-1 and immunoreactivity detected with a kit according to protocol. Immunoreactivity was detected with diaminobenzidine and sections counterstained with hematoxylin. Results showed that virtually all the cells of periodontal ligament, the vast majority representing fibroblasts, contained CRABP. Fibroblasts in the gingiva above the level of the alveolar crest also stained positively for CRABP. The periodontal tissues of all three molar teeth were similarly affected. Fibroblasts in other regions of the oral cavity, such as the dermis of the skin of the cheek or the lamina propria of the buccal mucosa or of the diastema region, exhibited little or no staining for CRABP. Because of its properties as a signaling molecule and its ability to interact with other regulatory molecules, retinoic acid and cellular retinoic acid-binding protein may play an important role in the biology of the periodontal tissues.