Ameloblastic fibroma (AF) and calcifying odontogenic cyst (COC, calcifying cystic odontogenic tumor according to WHO’s classification of 2005) are tumors that contain odontogenic epithelium and odontogenic ectomesenchyme

Background: Ameloblastin (AMBN) gene expresses an important protein that acts as a cell adhesion molecule. This protein plays an important role in maintaining the ameloblast secretory stage of differentiation by binding to them and inhibiting their proliferation. Due to the relationship of this protein in the differentiation and proliferation of odontogenic cells, here, we investigated this gene in different types of odontogenic tumors. Materials and Methods: Sequencing of the all encoding region of AMBN gene was carried out in four frozen cases of odontogenic tumors: one case of calcifying epithelial odontogenic tumor (CEOT), two calcifying odontogenic cysts (COC) and one ameloblastic fibroma (AF). Results: DNA sequencing was modified in an important domain of the AMBN only in the CEOT. Conclusion: The present study suggests that AMBN gene alterations may be relevant to the pathogenesis of CEOT. The presence of odontogenic epithelium and/or odontogenic ectomesenchyme is important in the classification of odontogenic tumors. The calcifying epithelial odontogenic tumor (CEOT) is a benign epithelial odontogenic tumor characterized by a locally invasive behavior and affects individuals ranging from 30 to 50 years of age (1). However, the molecular mechanisms associated with its development have not been established. Ameloblastic fibroma (AF) and calcifying odontogenic cyst (COC, calcifying cystic odontogenic tumor according to WHO’s classification of 2005) are tumors that contain odontogenic epithelium and odontogenic ectomesenchyme (2). AF occurs mainly in the first and second decades of life, affecting mandible rather than the maxilla (3). COC is a cystic odontogenic tumor with an epithelial lining containing ghost cells which may undergo calcification, closely resembling an ameloblastoma (4). Although the underlying genetic alterations are poorly understood in AF, mutations in the β catenin gene were described in COC (5). Some proteins of the enamel matrix have important roles in initiating cytodifferentiation of the dental tissue (6). Ameloblastin (AMBN) is the most important protein involved in these processes and is highly expressed during the differentiation of inner enamel epithelium (6, 7). The AMBN protein is a cell adhesion molecule essential for amelogenesis. It is localized near the cell surface and helps maintaining the ameloblast secretory stage of differentiation by binding to them and inhibiting their proliferation (8). The human AMBN gene has been cloned and comprises a singlecopy gene containing 13 exons with an open reading frame of 1,341 bp that encodes 447 amino acid 11 and maps to chromosome 4q21 (9). We have previously demonstrated that AMBN gene mutations are associated with the development of ameloblastoma, adenomatoid odontogenic tumor and squamous odontogenic tumor (10). As AMBN protein has an important role in the differentiation of ameloblasts and epithelium-mesenchyme signaling during odontogenesis, we prompted to investigate this gene in CEOT, COC and AF. Materials and Methods In this report, we studied one CEOT, two COC and one AF. Fragments of these tumors were obtained during surgical removal procedure, after an informed written consent was signed by all patients. The University Ethics Committee approved this work. One fragment was fixed in 10% formalin buffer and paraffinembedded tissue blocks were used for routine histological staining to confirm the clinical diagnosis. All four tumors studied showed typical histological features described in the literature (2, 4, 11). Specimen samples were immediately stored at –70 ̊C for subsequent molecular analyses. In addition, contra-lateral oral 3065 Correspondence to: Ricardo Santiago Gomez, Faculdade de Odontologia, Universidade Federal de Minas Gerais, Av. Antonio Carlos, 6627 Belo Horizonte, CEP 31270-901 MG, Brazil. Tel: +55 3134092477, Fax: +55 3134092430, e-mail: [email protected]