MAGI1 Recruits Dll1 to Cadherin-based Adherens Junctions and Stabilizes It on the Cell Surface

Abstract

Delta-Notch signaling plays an essential role in cell fate determination in many tissue types, including the central nervous system. Although the signaling mechanism of Notch has been extensively studied, the behaviors of its ligands are not well understood. In the present study, we found that, in the developing neural tube, Dll1(Delta-like 1) was mainly localized on the processes extending from nascent neurons toward both the pia and the ventricle and accumulated at apical termini, where adherens junctions (AJs) were formed. To understand the mechanism of Dll1 localization, we searched for binding proteins for Dll1 and identified a scaffolding molecule, MAGI1. In the developing spinal cord, MAGI1 mRNA was highly expressed in the ventricular zone, where Dll1 mRNA was expressed. MAGI1 protein accumulated at the AJs formed around the termini of apically extending processes and was partially colocalized with Dll1. MAGI1 bound not only to Dll1 but also to N-cadherin-␤-catenin complexes. In cultured AJ-forming fibroblasts, MAGI1 was localized at AJs, and Dll1 was recruited to these AJs through binding to MAGI1. In addition, Dll1 was stabilized on the cell surface by MAGI1. Taken together, these results suggest that Dll1 is presented on the surface of AJs formed at the apical termini of processes through interaction with MAGI1 to activate Notch on neighboring cells in the developing central nervous system.

Selective regulation of Notch ligands during angiogenesis is mediated by vimentin

“…S2A). Vimentin interacts with membrane-tethered proteins through PDZ motifs (48) and Jagged and Dll carry distinct PDZ sequences in their ICDs (49)(50)(51). Whereas the ECDs are important for receptor binding, the ICDs play important roles in signal activation through posttranslational modifications (37,52) and interactions with endocytic regulators (41)(42)(43).…”

“…The molecular basis requires further investigation but might involve specific sets of interacting proteins. Although the Jagged and Dll interactomes remain to be elucidated, the different ligands may have distinct links to the cytoskeleton (51,71). Vimentin interacts with membrane tethered proteins through PDZ motifs (48) and Jagged and Dll ligands carry distinct PDZ sequences in their intracellular domains (49)(50)(51).…”

“…Although the Jagged and Dll interactomes remain to be elucidated, the different ligands may have distinct links to the cytoskeleton (51,71). Vimentin interacts with membrane tethered proteins through PDZ motifs (48) and Jagged and Dll ligands carry distinct PDZ sequences in their intracellular domains (49)(50)(51). Clathrinmediated endocytosis (CME) of Dll depends on Epsin 1 and 2, together with the alternative adaptor protein clathrin assembly lymphoid myeloid leukemia protein (CALM), rather than AP2, which is central to CME of most proteins (42).…”

Delta expression in post‐mitotic neurons identifies distinct subsets of adult‐specific lineages in Drosophila

“…The challenge for future studies is to characterize the biological activity of Delta that is specific to neurite morphogenesis. The high degree of functional conservation of Delta seen across species so far, together with data that demonstrate a restricted pattern of Delta expression in nascent neuronal projections in the mouse neural tube (Mizuhara et al, 2005), are impetus for investigating a similar developmental program in the vertebrate CNS.…”

Endocytosis in Notch Signaling Activation

“…Starting from the N-terminus, the domain structure of the Notch ligands can be outlined as follows ( Fig.1): (i) a module at the N-terminus of Notch ligands (also known as the MNNL domain) of unknown structure but functionally relevant since Jag-1 mutations in this region are present in a subset of patients with the Alagille syndrome [99,100]; (ii) a DSL domain; (iii) a number of EGF-like repeats (ranging in number from 16 in the Jagged family to 5-9 in the Delta-like family); (iv) a cysteine-rich domain (CRD) present in Jagged but not in Dll ligands; (v) a transmembrane domain and (vi) an intracellular domain, highly divergent among Notch ligands, but with a conserved PDZ-binding domain in the mammalian Jagged-1, Delta-like-1 and -4. The function of this latter domain is unknown, although there is some evidence that its interaction with PDZ-containing adherens-junction proteins inhibits cell motility and favors epithelial cell assembly [101][102][103]. Similar to Notch receptors, Notch ligands undergo ectodomain shedding by ADAM metalloproteases [104,105] and RIP) by the presenilin/ -secretase complex [104] with the release of a C-terminal intracellular fragment (CTIF).…”