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Lai, E. C., Roegiers, F., Qin, X., Jan, Y. N. & Rubin, G. M. The ubiquitin ligase Drosophila Mind bomb promotes Notch signaling by regulating the localization and activity of Serrate and Delta. Development 132, 2319-2332

Fox Chase Cancer Center, Filadelfia, Pennsylvania, United States
Development (Impact Factor: 6.27). 06/2005; 132(10):2319-32. DOI: 10.1242/dev.01825
Source: PubMed

ABSTRACT The receptor Notch and its ligands of the Delta/Serrate/LAG2 (DSL) family are the central components in the Notch pathway, a fundamental cell signaling system that regulates pattern formation during animal development. Delta is directly ubiquitinated by Drosophila and Xenopus Neuralized, and by zebrafish Mind bomb, two unrelated RING-type E3 ubiquitin ligases with common abilities to promote Delta endocytosis and signaling activity. Although orthologs of both Neuralized and Mind bomb are found in most metazoan organisms, their relative contributions to Notch signaling in any single organism have not yet been assessed. We show here that a Drosophila ortholog of Mind bomb (D-mib) is a positive component of Notch signaling that is required for multiple Neuralized-independent, Notch-dependent developmental processes. Furthermore, we show that D-mib associates physically and functionally with both Serrate and Delta. We find that D-mib uses its ubiquitin ligase activity to promote DSL ligand activity, an activity that is correlated with its ability to induce the endocytosis and degradation of both Delta and Serrate (see also Le Borgne et al., 2005). We further demonstrate that D-mib can functionally replace Neuralized in multiple cell fate decisions that absolutely require endogenous Neuralized, a testament to the highly similar activities of these two unrelated ubiquitin ligases in regulating Notch signaling. We conclude that ubiquitination of Delta and Serrate by Neuralized and D-mib is an obligate feature of DSL ligand activation throughout Drosophila development.

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    • "In the first, we asked whether ectopic expression of Dl in the larval wing epithelium can induce wingless (wg), a Notch target gene normally found in the DV boundary (de Celis et al., 1996; Doherty et al., 1996; Neumann and Cohen, 1996). This event is known to be dependent on mib1 (Lai et al., 2005; Le Borgne et al., 2005; Pitsouli and Delidakis, 2005; Wang and Struhl, 2005), which is ubiquitously expressed in the wing disk. "
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    ABSTRACT: DSL proteins are transmembrane ligands of the Notch receptor. They associate with a RING (really interesting new gene) family E3 ubiquitin ligase, either Neuralized (Neur) or Mindbomb 1 (Mib1), as a prerequisite to signaling. Although Neur and Mib1 stimulate internalization of DSL ligands, it is not known how ubiquitylation contributes to signaling. We present a molecular dissection of the intracellular domain (ICD) of Drosophila melanogaster Delta (Dl), a prototype DSL protein. Using a cell-based assay, we detected ubiquitylation of Dl by both Neur and Mib1. The two enzymes use distinct docking sites and displayed different acceptor lysine preferences on the Dl ICD. We generated Dl variants that selectively perturb its interactions with Neur or Mib1 and analyzed their signaling activity in two in vivo contexts. We found an excellent correlation between the ability to undergo ubiquitylation and signaling. Therefore, ubiquitylation of the DSL ICD seems to be a necessary step in the activation of Notch.
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    • "molecular detail, as fundamental elements of the endocytic pathway have been shown to influence Delta function. A key set of observations centres on the requirements for the E3 ubiquitin ligases Neuralized (Neur) and Mind Bomb, which are thought to mono-ubiquitinate Delta (as well as Serrate, a second membrane-bound Notch ligand), thereby priming the ligands for endocytosis (Deblandre et al, 2001; Lai et al, 2001; Pavlopoulos et al, 2001; Yeh et al, 2001; Itoh et al, 2003; Lai et al, 2005; Le Borgne et al, 2005; Pitsouli and Delidakis, 2005; Wang and Struhl, 2005; Commisso and Boulianne, 2007). Two distinct, yet not necessarily exclusive models have been proposed to explain the involvement of endocytosis in potentiating Notch ligand function. "
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    ABSTRACT: Universal trafficking components within the cell can be recruited to coordinate and regulate the developmental signalling cascades. We will present ways in which the intracellular trafficking machinery is used to affect and modulate the outcome of signal transduction in developmental contexts, thus regulating multicellular development. Each of the signalling components must reach its proper intracellular destination, in a form that is properly folded and modified. In many instances, the ability to bring components together or segregate them into distinct compartments within the cell actually provides the switch mechanism to turn developmental signalling pathways on or off. The review will begin with a focus on the signal-sending cells, and the ways in which ligand trafficking can impinge on the signalling outcome, via processing, endocytosis and recycling. We will then turn to the signal-receiving cell, and discuss mechanisms by which endocytosis can affect the spatial features of the signal, and the compartmentalization of components downstream to the receptor.
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    • "It has also been suggested that differential expression of Drosophila Neur and Mib1 accounts for the requirements for these genes in distinct developmental events. In fact, we now know that Neur-independent Notch activation is due to the presence of Mib1, and in situations where both E3 ligases are expressed, simultaneous depletion of both Mib1 and Neur are required to produce loss-of-Notch phenotypes (Lai et al., 2005; Le Borgne et al., 2005; Pitsouli and Delidakis, 2005; Wang and Struhl, 2005). The finding that Neur and Mib1 function similarly in Drosophila provides strong support for ligand ubiquitylation as an absolute requirement for ligand signaling activity, rather than as a regulator of ligand levels or activity in limited developmental contexts. "
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    ABSTRACT: In the first volume of Developmental Cell, it was reported that the classic Drosophila neurogenic gene neuralized encodes a ubiquitin ligase that monoubiquitylates the Notch ligand Delta, thus promoting Delta endocytosis. A requirement for ligand internalization by the signal-sending cell, although counterintuitive, remains to date a feature unique to Notch signaling. Ten years and many ubiquitin ligases later, we discuss sequels to these three papers with an eye toward reviewing the development of ideas for how ligand ubiquitylation and endocytosis propel Notch signaling.
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