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Published February 1, 2001 | public
Journal Article

Differential Transcriptional Regulation of Individual TCR V Segments Before Gene Rearrangement


The promoter sequences of individual murine TCR Vβ segments are dissimilar, but any functional differences between them are masked after productive gene rearrangement by the dominance of the TCRβ 3′ enhancer. However, thymocytes of recombination-activating gene-2 (Rag2)-deficient mice allow the transcriptional activity of Vβ promoters to be studied before rearrangement. Here we report that many Vβ segments are detectably transcribed in Rag2^(−/−) thymocytes and that there are significant differences in expression among different Vβ segments. Primer extension and characterization of cDNA clones from SCID thymocytes suggest that these germline Vβ transcripts generally use the same start sites as those previously determined in mature T cells. The strength of expression before rearrangement does not correlate with proximity to the known enhancer, because members of the most distal Vβ cluster (Vβ2.1, Vβ1.1, Vβ4.1) are relatively strongly expressed and more proximal Vβ segments (Vβ14.1, Vβ3.1, Vβ7.1, Vβ6.1) are only weakly expressed. Different Vβ segments also show different developmental programs of activation in different thymocyte subsets, with the Vβ5.1(L)-8.2(V) spliced transcript expressed earliest as well as most strongly overall. Comparison with Rag^+ MHC class I^(−/−) and class II^(−/−) thymocytes confirms that many of these expression differences are leveled by rearrangement and/or by β selection, before MHC-dependent selection. However, the expression pattern of Vβ2.1 is highly distinctive and includes cell types apparently outside the T lineage, suggesting potential acquisition of specialized roles.

Additional Information

© 2001 The American Association of Immunologists. Received for publication October 10, 2000. Accepted for publication November 15, 2000. This work was supported by the DNA Sequencer Royalty Fund at Caltech. We thank Michele Anderson for the arrayed cDNA library from SCID thymocytes; Hua Wang for samples of sorted mutant thymocyte populations; Rochelle Diamond for expert assistance with the cell separations; Janice Telfer and Mary Yui for samples of fresh and IL-2 stimulated NK cells; Gabriela Hernandez-Hoyos for transgenic T cells expressing the AND-TCR; and members of the Rothenberg laboratory for valuable advice and suggestions. We also thank Ellen Robey (University of California, Berkeley, CA) for the gift of the MHC-deficient mouse breeding stock. This work was also made possible by the Caltech Biopolymer Synthesis Facility; by the Caltech Flow Cytometry and Cell Sorting Facility; and by Dana Miller and, later, employees of the Office of Laboratory Animal Research at Caltech who provided excellent care of the immunodeficient mice.

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