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Hedgehog signaling controls thymocyte progenitor homeostasis and differentiation in the thymus


Commitment of hematopoietic progenitors to the T cell lineage requires the integration of multiple signaling pathways. Evidence has suggested involvement of hedgehog (Hh) signaling in T cell differentiation through its signal transducer smoothened (Smo). However, the precise function of the Hh pathway remains controversial, mainly because T cell–specific in vivo genetic models have not been used. Using pre–T cell–specific, mature T cell–specific and poly(I)·poly(C)-inducible deletions of Smo and antagonists of Smo signaling, we report here that Hh is an essential positive regulator of T cell progenitor differentiation. Furthermore, we localize Hh function to a stage preceding pre–T cell receptor signaling, connect Smo signaling to the activity of the Gli1 and Gli2 transcription factors and demonstrate that Hh affects regulators of thymocyte survival and proliferation.

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We thank A. McMahon for Smoflox mice; J. McMahon for technical support; H. von Boehmer for support; H. Petrie, H. Nakase, W. Du, J. Pogoriler, J.-C. Zuniga-Pflucker, R. Wechsler-Reya, M. Allegre, F. Gounari, N. Liu and P. Ashton-Rickard for mice and materials; and B. Kee, J. Crispino and A. Wilson for discussions and critical review of the project. Supported by the Cancer Research Institute, the 'V' Foundation for Cancer Research, the Sidney Kimmel Foundation for Cancer Research (I.A.), the University of Chicago Medical Scientist Training Program (S.G.), the University of Chicago Committee on Cancer Biology (M.M.) and the Leukemia Research Foundation (M.M.).

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Competing interests

The authors declare no competing financial interests.

Correspondence to Iannis Aifantis.

Supplementary information

  1. Supplementary Fig. 1

    Shh expression in the adult thymus. (PDF 2569 kb)

  2. Supplementary Fig. 2

    Pre-T cell specific Smo deletion. (PDF 213 kb)

  3. Supplementary Fig. 3

    Effect of Smo deletion on thymic B and TCRγδ cell populations. (PDF 199 kb)

  4. Supplementary Fig. 4

    In vitro inhibition of Smo signaling affects development of (DN2) pro-T cells. (PDF 457 kb)

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Figure 1: Expression of Hh pathway elements in the thymus.
Figure 2: Efficient Smo deletion and Hh inhibition in the thymi of Smo−/floxLck-Cre+ mice.
Figure 3: Lck-Cre–mediated Smo deletion affects T cell differentiation.
Figure 4: T cell progenitors cannot differentiate in the absence of Hh signaling.
Figure 5: Mx1-Cre–induced Smo deletion affects thymic development.
Figure 6: Smo deficiency affects progenitor homeostasis and the expression of regulators of cell cycle and apoptosis.
Figure 7: Smo deficiency does not affect pre-TCR assembly or function.
Figure 8: 'Late', CD4-Cre–mediated Smo deletion fails to hinder T cell differentiation.