title: Identification of a bone marrow precursor of the earliest thymocytes in adult mouse.
abstract: The thymus requires continuous replenishment of progenitors from the bone marrow (BM) to sustain T cell development. However, it remains unclear which hematopoietic progenitors downstream from hematopoietic stem cells in the BM home to the thymus in adult mice. In this work, we demonstrate that although multiple BM populations have intrinsic T lineage differentiation potential, a small subset of multipotent progenitors (MPPs) expressing CCR9 preferentially homes to the thymus. These CCR9(+) MPPs are phenotypically similar to the most immature early T lineage progenitors (ETPs) in the thymus and are present in the peripheral blood. Similar to ETPs, CCR9(+) MPPs undergo Notch signaling, as indicated by higher expression of Notch1 and downstream target Hes1 genes compared with other MPP subsets. Furthermore, CCR9(+) MPPs possess differentiation potential similar to that of ETPs, with very limited granulocyte/macrophage differentiation potential, but they can differentiate into T, B, and dendritic cells. These characteristics implicate CCR9(+) MPPs as the BM precursors of the earliest thymic progenitors. In addition, our data suggest that before transition from BM to thymus, MPPs are lymphoid-specified and primed for T lineage differentiation.
authors.affiliation: Department of Immunology, Duke University Medical Center, Durham, NC 27710, USA.
authors.forename: Anne Y
authors.initials: AY
authors.lastname: Lai
authors.forename: Motonari
authors.initials: M
authors.lastname: Kondo
mesh_terms: D000818:Animals; D051792:Basic Helix-Loop-Helix Proteins / Q000378:metabolism; D002454:Cell Differentiation / Q000276:immunology*; D005434:Flow Cytometry; D006412:Hematopoietic Stem Cells / Q000166:cytology*; D018398:Homeodomain Proteins / Q000378:metabolism; D016130:Immunophenotyping; D051379:Mice; D039902:Multipotent Stem Cells / Q000166:cytology*; D051881:Receptor, Notch1 / Q000378:metabolism; D054388:Receptors, CCR; D019707:Receptors, Chemokine / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000276:immunology; D013601:T-Lymphocytes / Q000166:cytology*; D013950:Thymus Gland / Q000166:cytology* / Q000276:immunology; D000072056:Transcription Factor HES-1
chemical_list: D051792:Basic Helix-Loop-Helix Proteins; D018398:Homeodomain Proteins; D051881:Receptor, Notch1; D054388:Receptors, CCR; D019707:Receptors, Chemokine; D000072056:Transcription Factor HES-1; C119309:CC chemokine receptor 9; C489734:Hes1 protein, mouse; C497762:Notch1 protein, mouse