Direct comparison of Dll1- and Dll4-mediated Notch activation levels shows differential lympho-myeloid lineage commitment outcomes (36.27)

Abstract In the thymus, Notch signaling is known to be essential for T-lymphopoiesis, with the Notch ligand Delta like 4 (Dll4) being uniquely involved in this process. However, using stromal cell cultures, either Dll4 or Dll1 has been shown to support T-lymphopoiesis. To address which Dll is more effective at inducing hematopoietic progenitor cells to give rise to T-lineage cells in vitro, we generated OP9 cells expressing a series of incrementally discrete and equivalent levels of Dll1 or Dll4. In keeping with previous findings, OP9 cells expressing high levels of either Dll1 or Dll4 gave rise to T-lineage cells with similar efficacy, and prevented the differentiation of B- and myeloid-lineage cells. However, at limiting levels of Dll expression, Dll4 maintained its ability to inhibit B-lineage choice and induce T-lineage commitment and differentiation at lower levels of expression than Dll1. This manifest property of Dll4 is evident despite its lower levels of steady-state surface expression than Dll1 on OP9 cells. The heightened effectiveness of Dll4 over Dll1 also corresponded to the induction of expression of Notch target genes, and inhibition of B- and myeloid-specific transcription factors. Furthermore, OP9 cells expressing levels of Dll4 equivalent to those present in thymic epithelial cells gave rise to T-lineage cells, as expected, but were also permissive for the differentiation of myeloid cells, while still inhibiting the generation of B-lineage cells.