International Immunology Advance Access originally published online on November 1, 2007
International Immunology 2007 19(12):1421-1430; doi:10.1093/intimm/dxm113
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Constitutive Notch signalling promotes CD4–CD8– thymocyte differentiation in the absence of the pre-TCR complex, by mimicking pre-TCR signals
1 Division of Cancer Sciences and Molecular Pathology, Section of Experimental Haematology, Royal Infirmary, University of Glasgow, Glasgow G31 2ER, UK
2 Telethon Institute for Child Health Research, Cancer Biology Division, 100 Roberts Road, Subiaco, Western Australia 6008, Australia
3 Department of Immunology, Sunnybrook Research Institute, University of Toronto, 2075 Bayview Avenue, Toronto, Ontario M4N 3M5, Canada
4 Rosetta Inpharmatics LLC, 401 Terry Avenue North, Seattle, WA 98109, USA
5 Hopital Necker Enfants malades, INSERM U 768, Développement normal et pathologique du système immunitaire, Batiment KIRMISSON, 149 Rue de Sévres, 75743 Paris cedex 15, France
6 Ludwig Center for Cancer Genetics and Therapeutics, The Johns Hopkins Kimmel Cancer Center, 1650 Orleans Street, CRB 520, Baltimore, MD 21231, USA
7 Department of Pathology and Labortatory Medicine, University of Pennsylvania School of Medicine, 230 John Morgan Building, 36th and Hamilton Walk, Philadelphia, PA 19104-6082, USA
8 Division of Basic Science, Fox Chase Cancer Center, 333 Cottman Avenue, Philadelphia, PA 19111, USA
9 Haematology and Leukaemia, St Vincent's Institute, 9 Princes Street, Fitzroy, Victoria 3065, Australia
Correspondence to: D. J. Izon; E-mail: dizon{at}svi.edu.au
Notch1 signalling is essential for the commitment of multipotent lymphocyte precursors towards the 
ß T-cell lineage and plays an important role in regulating ß-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 ß-selection during early T-cell development by inducing pre-TCR-like signals within a T-cell-promoting environment.
Keywords: Notch, pre-TCR signalling, T-cell development, thymus
Transmitting editor: A. Singer
Received 15 July 2007, accepted 5 October 2007.