Fine-Scale Staging of T Cell Lineage Commitment in Adult Mouse Thymus

Abstract

T cell development is marked by the loss of alternative lineage choices accompanying specification and commitment to the T cell lineage. Commitment occurs between the CD4 and CD8 double-negative (DN) 2 and DN3 stages in mouse early T cells. To determine the gene regulatory changes that accompany commitment, we sought to distinguish and characterize the earliest committed wild type DN adult thymocytes. A transitional cell population, defined by the first down-regulation of surface c-Kit expression, was found to have lost the ability to differentiate into dendritic cells (DC) and natural killer (NK) cells when cultured without Notch-Delta signals. In the presence of Notch signaling, this subset generates T lineage descendants in an ordered precursor-product relationship between DN2, with the highest levels of surface c-Kit, and c-Kit-low DN3 cells. These earliest committed cells show only a few differences in regulatory gene expression as compared to uncommitted DN2 cells. They have not yet established the full expression of Notch-related and T cell differentiation genes characteristic of DN3 cells before β-selection. Instead, the downregulation of select stem cell and non-T lineage genes appears to be key to the extinction of alternative lineage choices.

SATB1 Plays a Critical Role in Establishment of Immune Tolerance

“…In the thymic microenvironment, Notch signaling is activated in these ETPs, which initiates T cell differentiation and shuts off developmental potential to other lineages (7)(8)(9). T lineage commitment is established during the DN2 stage, more specifically at the transition from the DN2a to the DN2b stage (10,11). Recombination of the TCRb genes is completed in the DN3 stage.…”

Notch Signaling During Human T cell Development

“…Within the CD34 + CD1 -uncommitted pool of progenitors, the thirdand by far largest -subset of thymocytes expresses high levels of CD7 and mainly comprises T/NK progenitors, resembling DN2a cells in the mouse (Yui et al, 2010). During postnatal life, these cells are most likely derived from Notch-primed CD34 + CD1a -CD7 -and/or CD34 + CD1a -CD7 int cells as they do not seem present within the bone marrow or peripheral blood (our own unpublished observations).…”

Bcl11b and combinatorial resolution of cell fate in the T-cell gene regulatory network

“…If the precursors can begin TCR expression successfully in DN3a, they continue through DN3b and DN4 to DP, when the cells finally acquire complete TCR recognition complexes (5,6). Importantly, if individual T-cell precursors in the ETP or DN2a stage are removed from thymic Notch ligands, they can still generate non-T cells, but from the DN2b stage on, they can no longer do this unless genetically manipulated (1,7). This transition defines "commitment.…”