The role of recombination activating gene (RAG) reinduction in thymocyte development in vivo.
Assembly of T cell receptor (TCR)alpha/beta genes by variable/diversity/joining (V[D]J) rearrangement is an ordered process beginning with recombination activating gene (RAG) expression and TCRbeta recombination in CD4(-)CD8(-)CD25(+) thymocytes. In these cells, TCRbeta expression leads to clonal expansion, RAG downregulation, and TCRbeta allelic exclusion. At the subsequent CD4(+)CD8(+) stage, RAG expression is reinduced and V(D)J recombination is initiated at the TCRalpha locus. This second wave of RAG expression is terminated upon expression of a positively selected alpha/beta TCR. To examine the physiologic role of the second wave of RAG expression, we analyzed mice that cannot reinduce RAG expression in CD4(+)CD8(+) T cells because the transgenic locus that directs RAG1 and RAG2 expression in these mice is missing a distal regulatory element essential for reinduction. In the absence of RAG reinduction we find normal numbers of CD4(+)CD8(+) cells but a 50-70% reduction in the number of mature CD4(+)CD8(-) and CD4(-)CD8(+) thymocytes. TCRalpha rearrangement is restricted to the 5' end of the Jalpha cluster and there is little apparent secondary TCRalpha recombination. Comparison of the TCRalpha genes expressed in wild-type or mutant mice shows that 65% of all alpha/beta T cells carry receptors that are normally assembled by secondary TCRalpha rearrangement. We conclude that RAG reinduction in CD4(+)CD8(+) thymocytes is not required for initial TCRalpha recombination but is essential for secondary TCRalpha recombination and that the majority of TCRalpha chains expressed in mature T cells are products of secondary recombination.
Yannoutsos
N
N
Laboratory of Molecular Immunology, The Rockefeller University, New York, NY 10021, USA. yannoun@mail.rockefeller.edu
Wilson
P
P
Yu
W
W
Chen
H T
HT
Nussenzweig
A
A
Petrie
H
H
Nussenzweig
M C
MC
D000818:Animals; D001483:Base Sequence; D017931:DNA Primers; D005786:Gene Expression Regulation; D016654:Genes, RAG-1 / Q000235:genetics*; D051379:Mice; D008822:Mice, Transgenic; D016693:Receptors, Antigen, T-Cell, alpha-beta / Q000235:genetics; D011995:Recombination, Genetic; D013950:Thymus Gland / Q000166:cytology*
D017931:DNA Primers; D016693:Receptors, Antigen, T-Cell, alpha-beta