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

Abstract

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.

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

“…Second, Bcl11b up-regulation depends on a stringently combinatorial action of GATA-3, TCF-1 (encoded by Tcf7), Runx1, and Notch signaling. Here, the most collaborative events appear necessary to "prime" the locus during the DN1 phase, before actual transcriptional activation in late DN2a phase (1). New results on E2A targets are considered further below.…”

“…This updated model incorporates recent data on functional impacts of E2A (22), on PU.1 and its interactions with Notch, Myb, and GATA-3 (21,23,24), on Notch blockade of the myeloid program via Hes1 against Cebpa (25, 26), on GATA-3 and its mutual antagonism with the B-cell program (27)(28)(29)(30), and on positive regulators of Bcl11b itself (1,31). Discussed in detail in SI Appendix, Supplementary Text, these results reveal two major switch circuits.…”

“…2A) (1), but the exact role of Bcl11b in this process depends on the unique regulatory context, which is not duplicated in any of the later T-cell contexts where Bcl11b works (reviewed in ref. 10) nor in type 2 ILC, where it also has a role (11,32,33).…”

“…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.…”

The making of a lymphocyte: the choice among disparate cell fates and the IKAROS enigma

“…Induction of TCF-1 and GATA-3 promotes survival and proliferation of early double-negative T-cell precursors (DN1 and DN2) (Germar et al 2011;Weber et al 2011). NOTCH1 signaling, TCF-1, GATA-3, and RUNX1, working together at the DN2 stage, up-regulate BCL11B, which further restricts differentiation into the αβ T-cell lineage (Ikawa et al 2010;Kueh et al 2016).…”