title: Notch1 and IL-7 receptor interplay maintains proliferation of human thymic progenitors while suppressing non-T cell fates.
abstract: Notch signaling is critical for T cell development of multipotent hemopoietic progenitors. Yet, how Notch regulates T cell fate specification during early thymopoiesis remains unclear. In this study, we have identified an early subset of CD34high c-kit+ flt3+ IL-7Ralpha+ cells in the human postnatal thymus, which includes primitive progenitors with combined lymphomyeloid potential. To assess the impact of Notch signaling in early T cell development, we expressed constitutively active Notch1 in such thymic lymphomyeloid precursors (TLMPs), or triggered their endogenous Notch pathway in the OP9-Delta-like1 stroma coculture. Our results show that proliferation vs differentiation is a critical decision influenced by Notch at the TLMP stage. We found that Notch signaling plays a prominent role in inhibiting non-T cell differentiation (i.e., macrophages, dendritic cells, and NK cells) of TLMPs, while sustaining the proliferation of undifferentiated thymocytes with T cell potential in response to unique IL-7 signals. However, Notch activation is not sufficient for inducing T-lineage progression of proliferating progenitors. Rather, stroma-derived signals are concurrently required. Moreover, while ectopic IL-7R expression cannot replace Notch for the maintenance and expansion of undifferentiated thymocytes, Notch signals sustain IL-7R expression in proliferating thymocytes and induce IL-7R up-regulation in a T cell line. Thus, IL-7R and Notch pathways cooperate to synchronize cell proliferation and suppression of non-T lineage choices in primitive intrathymic progenitors, which will be allowed to progress along the T cell pathway only upon interaction with an inductive stromal microenvironment. These data provide insight into a mechanism of Notch-regulated amplification of the intrathymic pool of early human T cell progenitors.
authors.affiliation: Centro de Biología Molecular Severo Ochoa, Consejo Superior de Investigaciones Científicas, Universidad Autónoma de Madrid, Madrid, Spain.
authors.forename: Marina
authors.initials: M
authors.lastname: García-Peydró
authors.forename: Virginia G
authors.initials: VG
authors.lastname: de Yébenes
authors.forename: María L
authors.initials: ML
authors.lastname: Toribio
mesh_terms: D000818:Animals; D002460:Cell Line; D049109:Cell Proliferation; D002478:Cells, Cultured; D002675:Child, Preschool; D006131:Growth Inhibitors / Q000502:physiology*; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D051379:Mice; D023461:Myeloid Progenitor Cells / Q000166:cytology* / Q000276:immunology / Q000378:metabolism; D009924:Organ Culture Techniques; D019009:Proto-Oncogene Proteins c-kit / Q000096:biosynthesis; D051881:Receptor, Notch1 / Q000378:metabolism / Q000502:physiology*; D020395:Receptors, Interleukin-7 / Q000378:metabolism / Q000502:physiology*; D015398:Signal Transduction / Q000276:immunology; D013601:T-Lymphocytes / Q000166:cytology* / Q000276:immunology* / Q000378:metabolism; D013950:Thymus Gland / Q000166:cytology* / Q000276:immunology / Q000378:metabolism; D051941:fms-Like Tyrosine Kinase 3 / Q000096:biosynthesis
chemical_list: D006131:Growth Inhibitors; C497761:NOTCH1 protein, human; D051881:Receptor, Notch1; D020395:Receptors, Interleukin-7; C497970:FLT3 protein, human; D019009:Proto-Oncogene Proteins c-kit; D051941:fms-Like Tyrosine Kinase 3