CELLULAR IMMUNOLOGY 169, 309–312 (1996) ARTICLE NO. 0123 SHORT COMMUNICATION Characterization of Cadherins Expressed by Murine Thymocytes SANDRA B. MUNRO,ALAIN J. DUCLOS,* ANDREW R. JACKSON, MALCOLM G. BAINES,* AND OREST W. BLASCHUK 1 Division of Urology, Department of Surgery, McGill University, Royal Victoria Hospital, 687 Pine Avenue West, Montreal, Quebec, Canada H3A 1A1; and *Department of Microbiology and Immunology, McGill University, 3775 University Street, Montreal, Quebec, Canada H3A 2B4 Received December 19, 1995; accepted February 18, 1996 transmembrane domain, and two cytoplasmic domains. In addition, they all contain the cell adhesion recogni- Thymocytes develop in close apposition to the stro- tion (CAR) sequence His-Ala-Val (HAV) in their first mal cells of the thymus. The ontogeny of thymocytes extracellular domain. The structural features of a sec- is dependent on intimate interactions between these ond group of cadherins, known as the atypical cadher- cells and the stromal cells. The molecular mechanisms involved in regulating thymocyte – stromal cell inter- ins (e.g., OB-cadherin), resemble those of the classical actions remain to be clearly defined. In this study, we cadherins, with the exception that the atypical cadher- utilized a polymerase chain reaction strategy to iden- ins lack the CAR sequence HAV in their first extracel- tify members of the cadherin family of cell adhesion lular domain (1–4). molecules that are expressed by CD4 / CD8 / thymo- Multiple biological functions have been attributed cytes, the major cell type in the thymus. One classical to the classical cadherins (reviewed in ref. 1). For ex- cadherin (E-cadherin), three atypical cadherins (OB- ample, the classical cadherins have been shown to be cadherin, K-cadherin, and cadherin-8), and two novel capable of promoting calcium-dependent cell adhe- cadherins (T1-cadherin and T2-cadherin) were found sion, the formation of intercellular junctions, the es- to be expressed by the CD4 / CD8 / thymocytes. The tablishment of cell polarity, and cell sorting during discovery that these cells display multiple cadherins development. In contrast, the biological properties of opens a new area of investigation concerning the adhe- the atypical cadherins have not yet been elucidated, sive mechanisms involved in modulating thymocyte – nor has their tissue distribution been thoroughly doc- stromal cell interactions. We speculate that cadherins umented. will prove to play an essential role in the ontogeny of A recent study revealed the presence of the classical thymocytes.  1996 Academic Press, Inc. cadherin, known as E-cadherin, in the thymus (5). This cell adhesion molecule (CAM) was found to be INTRODUCTION displayed by the thymocytes and stromal (epithelial) cells of this tissue. Furthermore, the levels of E-cad- The cadherins are a gene superfamily of calcium- herin in the thymus were shown to be developmen- binding, membrane glycoproteins (reviewed in ref. 1). tally regulated, with early immature thymocytes Members of this superfamily can be placed into one of (characterized by the lack of the cell surface antigens nine groups. The most intensively studied group of CD4 and CD8) expressing high levels of this CAM, in these membrane glycoproteins is known as the classical comparison to thymocytes of intermediate maturity cadherins (e.g., E-cadherin). These cadherins mediate (characterized by the presence of CD4 and CD8; desig- cell adhesion by a homophilic mechanism. All of the nated as CD4 / CD8 / thymocytes). Based on these ob- classical cadherins are integral membrane glycopro- servations, the hypothesis was presented that E- teins composed of five extracellular domains, a single cadherin may play a role in regulating adhesive inter- actions between these two cell types. Cadherins may therefore prove to be important regulators of thymo- 1 To whom correspondence and reprint requests should be ad- dressed. Fax: (514) 843-1457. E-mail: mdob@musica.mcgill.ca. cyte development, as the ontogeny of these cells is 309 0008-8749/96 $18.00 Copyright  1996 by Academic Press, Inc. All rights of reproduction in any form reserved.