Constitutive Notch signalling promotes CD4 CD8 thymocyte differentiation in the absence of the pre TCR complex, by mimicking pre TCR signals.
Notch1 signalling is essential for the commitment of multipotent lymphocyte precursors towards the alphabeta T cell lineage and plays an important role in regulating beta selection in CD4( )CD8( double negative (DN) thymocytes. However, the role played by Notch in promoting the development of CD4()CD8( double positive (DP) thymocytes is poorly characterized. Here, we demonstrate that the introduction of a constitutively active Notch1 (ICN1) construct into RAG( lymphocyte precursors resulted in the generation of DP thymocytes in in vitro T cell culture systems. Notably, developmental rescue was dependent not only on the presence of an intact Notch1 RAM domain but also on Delta like signals, as ICN1 induced DP development in RAG( thymocytes occurred within an intact thymus or in OP9 DL1 co cultures, but not in OP9 control co cultures. Interestingly, ICN1 expression in SLP 76( precursors resulted in only a minimal developmental rescue to the immature CD8( single positive stage, suggesting that Notch is utilizing the same signalling pathway as the pre TCR complex. In support of this, ICN1 introduction resulted in the activation of the ERK MAPK signalling cascade in RAG( thymocytes. Taken together, these studies demonstrate that constitutive Notch signalling can bypass beta selection during early T cell development by inducing pre TCR like signals within a T cell promoting environment.
International immunology