Divergent functions and distinct localization of the Notch ligands DLL1 and DLL3 in vivo

Abstract

The Notch ligands Dll1 and Dll3 are coexpressed in the presomitic mesoderm of mouse embryos. Despite their coexpression, mutations in Dll1 and Dll3 cause strikingly different defects. To determine if there is any functional equivalence, we replaced Dll1 with Dll3 in mice. Dll3 does not compensate for Dll1; DLL1 activates Notch in Drosophila wing discs, but DLL3 does not. We do not observe evidence for antagonism between DLL1 and DLL3, or repression of Notch activity in mice or Drosophila. In vitro analyses show that differences in various domains of DLL1 and DLL3 individually contribute to their biochemical nonequivalence. In contrast to endogenous DLL1 located on the surface of presomitic mesoderm cells, we find endogenous DLL3 predominantly in the Golgi apparatus. Our data demonstrate distinct in vivo functions for DLL1 and DLL3. They suggest that DLL3 does not antagonize DLL1 in the presomitic mesoderm and warrant further analyses of potential physiological functions of DLL3 in the Golgi network.

Canonical and Non-Canonical Notch Ligands

“…Mutational and structural studies indicate a contributory role for the DOS domain in Notch binding and signaling distinguishing them from the remaining EGF-like repeats (Cordle et al, 2008; Komatsu et al, 2008; Parks et al, 2006; Shimizu et al, 1999). In particular, the sequence and spacing within the DOS are important for signaling (Geffers et al, 2007). Furthermore, mutations associated with Alagille syndrome and the congenital disorder Tetralogy of Fallot map to the DOS motif of Jagged1, highlighting the importance of this region in Notch signaling (Eldadah et al, 2001; Guarnaccia et al, 2009; Warthen et al, 2006).…”

“…Although these structural features are critical for ligand signaling activity, losses in Dll3 are associated with vertebral segmentation and rib malformations similar to those caused by defects in Notch signaling (Dunwoodie, 2009). Dll3, however, does not bind Notch in trans or activate Notch signaling (Ladi et al, 2005), and the majority of Dll3 is detected in the Golgi, with relatively little, if any, cell surface expression (Geffers et al, 2007). Gene replacement studies in mice clearly show that Dll3 cannot substitute for the loss of Dll1 (Geffers et al, 2007), indicating that these DSL ligands are not functionally equivalent.…”

“…Dll3, however, does not bind Notch in trans or activate Notch signaling (Ladi et al, 2005), and the majority of Dll3 is detected in the Golgi, with relatively little, if any, cell surface expression (Geffers et al, 2007). Gene replacement studies in mice clearly show that Dll3 cannot substitute for the loss of Dll1 (Geffers et al, 2007), indicating that these DSL ligands are not functionally equivalent. In contrast to Dll1 that both activates and inhibits Notch signaling, Dll3 functions exclusively as a Notch antagonist (Ladi et al, 2005).…”

A DLL3-targeted antibody-drug conjugate eradicates high-grade pulmonary neuroendocrine tumor-initiating cells in vivo

“…The mammalian Notch family ligands DLL1, DLL4, JAG1, and JAG2 each activate Notch receptor signaling in trans (26). In contrast, the related ligand delta-like 3 (DLL3) predominantly localizes to the Golgi apparatus and is unable to activate Notch signaling (27, 28). DLL3 shares only 36% homology with DLL1 and differs from other deltatype DSL (Delta/Serrate/LAG-2) proteins, DLL1 and DLL4, in both its reduced number of epidermal growth factor (EGF)–like repeats and spacing of the cysteine residues within its DSL domain, which is required for Notch binding (29).…”

“…DLL3 shares only 36% homology with DLL1 and differs from other deltatype DSL (Delta/Serrate/LAG-2) proteins, DLL1 and DLL4, in both its reduced number of epidermal growth factor (EGF)–like repeats and spacing of the cysteine residues within its DSL domain, which is required for Notch binding (29). Normal tissue expression of DLL3 is highest in fetal brain, and DLL3 plays a key role in somitogenesis in the paraxial mesoderm (27, 28, 30–32). Although Notch pathway activation acts as an oncogenic stimulus in some tumor types (33), Notch activation in neuroendocrine tumors suppresses tumor growth (34).…”