Asynchronous combinatorial action of four regulatory factors activates Bcl11b for T cell commitment

During T cell development, multipotent progenitors relinquish competence for other fates and commit to the T cell lineage by turning on the transcription factor Bcl11b. To clarify lineage commitment mechanisms, we followed developing T cells at single-cell level using Bcl11b knock-in fluorescent reporter mice. Notch signaling and Notch-activated transcription factors collaborate to activate Bcl11b expression, irrespective of Notch-dependent proliferation. These inputs work via three distinct, asynchronous mechanisms: an early locus poising function dependent on TCF-1 and GATA-3; a stochastic permissivity function dependent on Notch signaling; and a separate amplitude-control function dependent on Runx1, a factor already present in multipotent progenitors. Despite all being necessary for Bcl11b activation, these inputs act in a stage specific manner, providing a multi-tiered mechanism for developmental gene regulation.