Interleukin-7 co-ordinates proliferation, differentiation and Tcra recombination during thymocyte β-selection

pre-T cell receptor (TCR) and Notch signaling induce transient self-renewal or “β-selection” of TCRβ(+) CD4 CD8 double-negative-3 (DN3) and DN4 progenitors that differentiate into CD4 CD8 double positive (DP) thymocytes which then rearrange Tcra. Interleukin-7 (IL-7) promotes Bcl2-dependent survival of TCRβ(−) DN thymocytes, but IL-7 functions during β-selection remain unclear. Here, we show that IL-7 signals TCRβ(+) DN3 and DN4 thymocytes to upregulate genes involved in cell growth and represses Bcl6. Accordingly, IL-7-deficient DN4 cells lacked trophic receptors and did not proliferate, but rearranged Tcra prematurely and differentiated rapidly. Bcl6 deletion, but not BCL2 over-expression, partially restored DN4 self-renewal in the absence of IL-7. Thus, IL-7 critically collaborates with pre-TCR and Notch signaling to coordinate proliferation, differentiation and Tcra recombination during β-selection.