Podoplanin, a transmembrane glycoprotein that was originally detected in puromycin-induced nephrosis on the surface of rat podocytes, is expressed specifically by lymphatic endothelium. Recent studies have shown that the protein is expressed in a variety of normal as well as neoplastic tissues, and that its expression might be related to cell migration and invasion. In this review, we describe the expression and function of podoplanin under normal as well as pathological conditions of the oral and maxillofacial regions, and we discuss its significance.

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Background: Adenoid cystic carcinoma (AdCC) displays morphological diversity within its characteristic tumor cell nests, which are primarily classified into tubular, cribriform, and solid patterns. Such histological diversity should result from the proportional proliferation between neoplastic myoepithelial cells (NMC)/basal cells and ductal epithelial cells. The aim of this study was to clarify the relationship between this morphological diversity and the development of AdCC in the salivary gland using double immunostaining with monoclonal antibodies to p16 and p63 gene products. Methods: We examined 10 samples of formalin-fixed, paraffin-embedded AdCC tissues. Results: In the normal salivary gland, p16 protein (P16) was not expressed in any cells, whereas p63 protein (P63)-positivities were observed in ductal basal cells and in acinar myoepithelial cells. In AdCC foci showing the tubular pattern, P16 expression was localized in the inner cells of the ductal structure, while P63 was localized in the outer NMC of them within the same sections. In tumor foci with the cribriform pattern, P16 was expressed in several cells forming pseudocysts and in some of the inner cells. P63 was expressed in many cells in the cancer nests. In those with the solid pattern, P16 and P63 were intermixed within the same foci. Conclusions: Thus, the double immunohistochemistry for P16 and P63 was useful for observing the morphological diversity of AdCC cells within the same foci on the same tissue section. These data suggest that P16 and P63 may play important roles in the morphological diversity and development of AdCC tissue architectures.

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=Background: The major function of epithelial rests of Malassez (ERM) cells is to maintain the homeostasis of the periodontal ligament (PDL). The purpose of this study was to characterize the effects of ERM cells on PDL fibroblasts in vitro using a co-culture system. Methods: PDL fibroblasts and ERM cells derived from porcine tissues were used. PDL fibroblasts were seeded in 6-welldishes. ERM cells plated in a chamber with a 0.4 μm pore membrane, were placed into the wells for 5 days. Osteocalcin (OCN), bone sialoprotein (BSP), osteoprotegerin (OPG) and receptor activator of NF-k B ligand (RANKL) mRNA levels in the PDL fibroblasts were then analyzed using real time RT-PCR. Alkaline phosphatase (ALP) activity was also measured. PDL fibroblasts cultured without ERM cells were used as a control. Results: OCN, BSP and OPG mRNA levels in PDL fibroblasts co-cultured with ERM cells were lower than the levels in the control group. Meanwhile, the RANKL mRNA level in PDL fibroblasts co-cultured with ERM cells was significantly higher than that of the controls (P<0.01). ALP activity of PDL fibroblasts co-cultured with ERM cells was significantly lower than in the controls (P<0.01). Conclusion: This study shows that ERM cells affect the functions of PDL fibroblasts, which decrease hard tissue formation and increase bone resorption. Therefore, ERM cells prevent dento-alveolar ankylosis of the PDL.

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