Immunolocalization of CD44 and heparan sulfate chains on the stratum intermedium and papillary layer in the rat enamel organ.

We studied the immunohistochemical localization of CD44 and heparan sulfate (HS) chains in rat enamel organ by confocal laser scanning microscopy and transmission electron microscopy. We also investigated the binding sites of basic fibroblast growth factor (bFGF), one of the heparin-binding growth factors (HBGF), on Microslicer-sections to clarify its role in the cell-cell interaction of HS. At the differentiation stage of ameloblast, weak immunoreactivity for CD44 was detected on the plasma membrane of the inner enamel epithelium, external enamel epithelium and the cells adjacent to the inner enamel epithelium. In accordance with the differentiation of preameloblasts into secretory ameloblasts, this immunoreactivity increased in stratum intermedium cells. At the secretory stage, stratum intermedium cells showed the most intense immunoreactivity in the enamel organ. At the maturation stage, strong immunoreactivity was seen on papillary layer cells. On the other hand, the lateral plasma membrane of ruffle-ended (RA) and smooth-ended ameloblast (SA) showed weak reactivity. No immunoreactivity was detected on the ruffled border of RA and the distal plasma membrane of SA. Immunolocalization of HS chains was similar to that of CD44. The binding activity of bFGF was also intense on stratum intermedium cells and papillary layer cells. These findings suggest that: 1) stratum intermedium cells and papillary layer cells express CD44 and HS chains in accordance with their differentiation; 2) HS chains on the plasma membrane of these cells may regulate calcium transport by their negative charge; and 3) HS chains on the stratum intermedium and papillary layer may play an important role in the differentiation and activity of ameloblasts by preserving HBGF.