Comparative gene-expression analysis of dental follicle and periodontal ligament in humans

Abstract

AbstractComparative gene-expression analysis ofdental follicle and periodontal ligament in humansJongeun LeeDeptartment of Dental Science, The Graduate School, Yonsei University(Directed by professor Byung Jai Choi, D.D.S., M.S., Ph.D.)The human dental follicle (hDF) surrounds the developing tooth germ and it contains the progenitor cells of periodontium that is composed of the periodontal ligament (PDL), alveolar bone, and the mineralized bone-like cementum covering the tooth root surface. One of the biological functions of the dental follicle is the coordination of tooth eruption. Moreover this tissue harbours progenitor cells for the periodontium. The PDL tissue is one of the components of the periodontium that connects the tooth to the alveolar jaw bone in the area surrounding the root surfaces. The functions of PDL are to support the tooth, to maintain homeostasis and to absorb mechanical stress during traumatic tooth injury.Although, several studies about gene expression and differentiation of hDF already exist, there is no comparative study of hDF and PDL as yet. For that reason this study was conducted to compare the gene expression profile of hDF with PDL and to evaluate the functions of these by using cDNA microarray, quantative real-time polymerase chain reaction (RT-PCR) and immunohistochemical staining. Microarray analysis has identified 490 genes with a twofold or greater difference in expression level between hDF and PDL, 365 and 125 of which were more abundant in hDF and PDL, respectively. Genes related to enamel matrix formation and mineralization such as those encoding ameloblastin (AMBN) and amelotin (AMTN) and to the regulation of cell cycle, proliferation, and developmental processes such as encoding EGF-like-domain, multiple 6 (EGFL6) and to promoting the migration of B lymphocytes, such as chemokine (C-X-C motif) ligand 13 (CXCL13), were more strongly expressed in dental follicle than periodontal ligament in humans. Quantative RT-PCR analysis was conducted for six selected genes. The expressions of AMTN, EGFL-6, CXCL13, and MMP8 were up-regulated in dental follicle tissue. DMP1, WIF1, and CD36 were up-regulated in PDL tissue. These results were consistent with the microarray results.Immunohistochemical (IHC) staining results were as follows: AMTN was stained only in reduced enamel epithelium of dental follicle. CXCL13 was broadly stained in the outer area of dental follicles and also stained in Hertwig’s epithelial root sheath (HERS). DMP1 was not stained in dental follicles but stained around the cementoblasts layer. WIF1 was not stained in dental follicles, but strongly stained in permanent PDL tissues, especially the cementoblasts layer. MMP9 was broadly stained in the outer area of dental follicles but also strongly stained in total layers of permanent PDL tissues. The results were consistent with those of the cDNA microarray analysis in the protein level.