ORIGINAL PAPER Med Mol Morphol (2009) 42:212–215 © The Japanese Society for Clinical Molecular Morphology 2009 DOI 10.1007/s00795-009-0464-9 Masato Saitoh · Yoshito Kurashige · Michiko Nishimura Mami Yamazaki · Seiji Igarashi · Tohru Kaku Yoshihiro Abiko Expression of claudin-4 and -7 in porcine gingival junctional epithelium Abstract Junctional epithelium, a nonkeratinized stratified epithelium, extends apically in apposition to the surface of the enamel to form a seal between the epithelium and the tooth. Desmosomes and gap junctions adhere to the junc- tional epithelium through cell–cell contact, but no evidence of tight junctions has been found. Recently, tight junction hallmark proteins and tight junction-related structures have been identified in stratified squamous epithelium. The present study examined whether tight junction proteins were expressed in the junctional epithelium. We used immunohistochemical techniques to observe expression of claudin-1, -4, -5, -7, and occludin in porcine gingival junc- tional epithelium. Claudin-4 exhibited immunoreactivity in the intercellular spaces of all layers of the oral epithelium and the junctional epithelium. Stronger expression was observed in junctional epithelial cells adjacent to the inner and outer basal laminae than in the inner cell layers. Immu- nohistochemical positivity for claudin-7 was clearly observed in the junctional epithelium, but only a faint positivity was observed in the basal layer of the oral epithelium. No immu- nohistochemical positivity for claudin-1, -5, or occludin was observed in the junctional epithelium. RT-PCR assay con- firmed expression of porcine claudin-4 and -7 mRNAs in the junctional epithelium. These findings indicate that M. Saitoh Department of Dental Science, Institute of Personalized Medical Science, Hokkaido, Japan M. Saitoh · Y. Kurashige · S. Igarashi Division of Pediatric Dentistry, Department of Oral Growth and Development, Health Sciences University of Hokkaido, Hokkaido, Japan M. Nishimura · M. Yamazaki · T. Kaku · Y. Abiko Division of Clinical Oral Pathology, Department of Human Biology and Pathophysiology, School of Dentistry, Health Sciences University of Hokkaido, Hokkaido, Japan Y. Abiko (*) Division of Oral Medicine and Pathology, Department of Dental Science, Institute of Personalized Medical Science, Health Sciences University of Hokkaido, 2-5 Ainosato, Kita-ku, Sapporo, Hokkaido 002-8072, Japan Tel. +81-11-778-7557; Fax +81-11-770-5034 e-mail: yoshi-ab@hoku-iryo-u.ac.jp claudin-4 and -7 may play a role in the junctional epithelium even in the absence of tight junctions. Key words Claudin · Tight junction · Stratified squamous epithelium · Oral gingival epithelium · Junctional epithelium Introduction The gingiva is located around the neck of each tooth and resists the forces of mastication. It is composed of gingival epithelium and gingival connective tissue. The gingival epi- thelium is classified into gingival oral epithelium, sulcular epithelium, and junctional epithelium. The junctional epi- thelium, a nonkeratinized epithelium, forms the floor of the gingival sulcus and extends apically in apposition to the surface of the enamel to form a seal between the epithelium and the tooth. The junctional epithelium is characterized by wide intercellular spaces as a result of the reduced number of desmosomes. The intercellular spaces contain varying numbers of neutrophils. In addition to the desmosomes, gap junctions are formed by cell–cell contact of the junctional epithelium. 1 A further type of intercellular junction, the tight junction, is considered less important in stratified squamous epithelia such as epidermis, oral epithelium, and junctional epithelium because the abundance of desmo- somes mediates a firm mechanical stability between the cells. Tight junctions are composed of three major trans- membrane proteins, namely claudin, occludin, and junc- tional adhesion molecules. 2–4 Claudins fulfill a barrier function in epithelial and endothelial tissues as they are thought to be responsible for the variety of electrical resis- tance and paracellular ionic selectivity seen in epithelia and endothelia. 5–7 The claudin family consists of 24 members, and four transmembrane domains have been identified in different species. The claudins show specific patterns of expression in different tissues. 8 Occludin may be more important for cell signaling than for forming the paracellu- lar barrier. 9,10 Recent reports have demonstrated localiza- Received: April 30, 2009 / Accepted: July 17, 2009