Context-Dependent Functional Divergence of the Notch Ligands DLL1 and DLL4 In Vivo

Abstract

Notch signalling is a fundamental pathway that shapes the developing embryo and sustains adult tissues by direct communication between ligand and receptor molecules on adjacent cells. Among the ligands are two Delta paralogues, DLL1 and DLL4, that are conserved in mammals and share a similar structure and sequence. They activate the Notch receptor partly in overlapping expression domains where they fulfil redundant functions in some processes (e.g. maintenance of the crypt cell progenitor pool). In other processes, however, they appear to act differently (e.g. maintenance of foetal arterial identity) raising the questions of how similar DLL1 and DLL4 really are and which mechanism causes the apparent context-dependent divergence. By analysing mice that conditionally overexpress DLL1 or DLL4 from the same genomic locus (Hprt) and mice that express DLL4 instead of DLL1 from the endogenous Dll1 locus (Dll1Dll4ki), we found functional differences that are tissue-specific: while DLL1 and DLL4 act redundantly during the maintenance of retinal progenitors, their function varies in the presomitic mesoderm (PSM) where somites form in a Notch-dependent process. In the anterior PSM, every cell expresses both Notch receptors and ligands, and DLL1 is the only activator of Notch while DLL4 is not endogenously expressed. Transgenic DLL4 cannot replace DLL1 during somitogenesis and in heterozygous Dll1Dll4ki/+ mice, the Dll1Dll4ki allele causes a dominant segmentation phenotype. Testing several aspects of the complex Notch signalling system in vitro, we found that both ligands have a similar trans-activation potential but that only DLL4 is an efficient cis-inhibitor of Notch signalling, causing a reduced net activation of Notch. These differential cis-inhibitory properties are likely to contribute to the functional divergence of DLL1 and DLL4.

Excitable Dynamics and Yap-Dependent Mechanical Cues Drive the Segmentation Clock

“…Notch1 and DLL1 oscillations could underlie the pulse dynamics (Bone et al, 2014; Kim et al, 2011; Liao et al, 2016; Shimojo and Kageyama, 2016). However, restoration of non-oscillatory expression of DLL1 in the mouse PSM leads to the formation of normal somites (Preusse et al, 2015). Our data suggest that in the excitable regime, Notch signaling is required both for the initiation ( i.e.…”

Cell autonomous and nonautonomous requirements for Delltalike1 during early mouse retinal neurogenesis

“…In the optic cup, Dll1 mRNA is first detectable at E10.5, just ahead of the first wave of neurons at E11.0 (Bao and Cepko, ; Rocha et al, ; Luo et al, ). By midgestation, about 80% of Dll4 + retinal cells coexpress Dll1 , suggesting that Dll1 activity starts earlier and acts more broadly (Rocha et al, ; Preusse et al, ). It further implies that Dll1 and Dll4 laterally inhibit neighboring RPCs, largely by signaling from postmitotic cells.…”

“…By comparison, Notch1 receptor mutants have a profound reduction of proliferating RPCs (Jadhav et al, 2006;Yaron et al, 2006). A recent study also showed that Dll4 substitution into the Dll1 locus fully rescued the Dll1 RPC phenotype (Preusse et al, 2015). Thus, in the early retina it seems clear that Dll1 and Dll4 redundancy reinforces the lateral inhibition signal (in trans) to neighboring Notchþ, Hes1þ RPCs.…”

DLL4+ dendritic cells: Key regulators of Notch Signaling in effector T cell responses

“…15,17,56 Besides, DLL4 is ~50% identical to DLL1 at the amino acid level. 57 These structure differences and the dramatic difference of amino acid sequence among Notch ligands may explain their functional differences.…”