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T Cell Lineage Determination Precedes the Initiation of TCR Gene Rearrangement¹

Kyoko Masuda^*,, Kiyokazu Kakugawa^*, Toshinori Nakayama, Nagahiro Minato, Yoshimoto Katsura and Hiroshi Kawamoto^2,*

^* Laboratory for Lymphocyte Development, RIKEN Research Center for Allergy and Immunology, Yokohama, Japan; Department of Immunology and Cell Biology, Graduate School of Biostudies, Kyoto University, Kyoto, Japan; Department of Immunology, Graduate School of Medicine, Chiba University, Chiba, Japan; and Division of Cell Regeneration and Transplantation, Advanced Medical Research Center, Nihon University School of Medicine, Tokyo, Japan

Loss of dendritic cell potential is one of the major events in intrathymic T cell development, during which the progenitors become determined to the T cell lineage. However, it remains unclear whether this event occurs in synchrony with another important event, TCR chain gene rearrangement, which has been considered the definitive sign of irreversible T cell lineage commitment. To address this issue, we used transgenic mice in which GFP expression is controlled by the lck proximal promoter. We found that the double-negative (DN) 2 stage can be subdivided into GFP^– and GFP⁺ populations, representing functionally different developmental stages in that the GFP^–DN2, but not GFP⁺DN2, cells retain dendritic cell potential. The GFP⁺DN2 cells were found to undergo several rounds of proliferation before the initiation of TCR rearrangement as evidenced by the diversity of D-J rearrangements seen in T cells derived from a single GFP⁺DN2 progenitor. These results indicated that the determination step of progenitors to the T cell lineage is a separable event from TCR rearrangement.

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¹ This work was supported by the Special Coordination Funds for Promoting Science and Technology from the Ministry of Education, Culture, Sports, Science and Technology of Japan.

² Address correspondence and reprint requests to Dr. Hiroshi Kawamoto, Laboratory for Lymphocyte Development, RIKEN Research Center for Allergy and Immunology, 1-7-22, Suehiro-cho, Tsurumi-ku, Yokohama 230-0045, Japan. E-mail address: kawamoto{at}rcai.riken.jp

³ Abbreviations used in this paper: DC, dendritic cell; DN, double negative; dpc, days post coitum; rm, recombinant murine; SCF, stem cell factor; Flt3L, Flt3 ligand; FT, fetal thymus; dGuo, deoxyguanosine; PI, propidium iodide; AT, adult thymus; DP, double positive; SP, single positive.