Article thumbnail

The Functions of Auxilin and Rab11 in Drosophila Suggest That the Fundamental Role of Ligand Endocytosis in Notch Signaling Cells Is Not Recycling

By Susan M. L. Banks, Bomsoo Cho, Suk Ho Eun, Ji-Hoon Lee, Sarah L. Windler, Xuanhua Xie, David Bilder and Janice A. Fischer


Notch signaling requires ligand internalization by the signal sending cells. Two endocytic proteins, epsin and auxilin, are essential for ligand internalization and signaling. Epsin promotes clathrin-coated vesicle formation, and auxilin uncoats clathrin from newly internalized vesicles. Two hypotheses have been advanced to explain the requirement for ligand endocytosis. One idea is that after ligand/receptor binding, ligand endocytosis leads to receptor activation by pulling on the receptor, which either exposes a cleavage site on the extracellular domain, or dissociates two receptor subunits. Alternatively, ligand internalization prior to receptor binding, followed by trafficking through an endosomal pathway and recycling to the plasma membrane may enable ligand activation. Activation could mean ligand modification or ligand transcytosis to a membrane environment conducive to signaling. A key piece of evidence supporting the recycling model is the requirement in signaling cells for Rab11, which encodes a GTPase critical for endosomal recycling. Here, we use Drosophila Rab11 and auxilin mutants to test the ligand recycling hypothesis. First, we find that Rab11 is dispensable for several Notch signaling events in the eye disc. Second, we find that Drosophila female germline cells, the one cell type known to signal without clathrin, also do not require auxilin to signal. Third, we find that much of the requirement for auxilin in Notch signaling was bypassed by overexpression of both clathrin heavy chain and epsin. Thus, the main role of auxilin in Notch signaling is not to produce uncoated ligand-containing vesicles, but to maintain the pool of free clathrin. Taken together, these results argue strongly that at least in some cell types, the primary function of Notch ligand endocytosis is not for ligand recycling

Topics: Research Article
Publisher: Public Library of Science
OAI identifier:
Provided by: PubMed Central

To submit an update or takedown request for this paper, please submit an Update/Correction/Removal Request.

Suggested articles


  1. (2000). A yeast DNA J protein required for uncoating of clathrin coated vesicles in vivo.
  2. (1999). Asymmetric activation specifies photoreceptors R3 and R4 and planar polarity in the Drosophila eye.
  3. (2005). Asymmetric Rab11 endosomes regulate Delta recycling and specify cell fate in the Drosophila nervous system.
  4. (2008). Auxilin is essential for Delta signaling.
  5. (1987). Cell fate in the Drosophila ommatidium.
  6. (1991). Characterization and spatial distribution of the ELAV protein during Drosophila melanogaster development.
  7. (2005). Clathrinindependent endocytosis of ubiquitinated cargos.
  8. (1999). Decoding vectorial information from a gradient: sequential roles of the receptors Frizzled and Notch in establishing planar polarity in the Drosophila eye.
  9. (2010). Disruption of zebrafish cyclin G-associated kinase (GAK) function impairs the expression of Notch-dependent genes during neurogenesis and causes defects in neuronal development.
  10. (2005). Distinct roles for Mind bomb, Neuralized, and epsin in mediating DSL endocytosis and signaling in Drosophila.
  11. (2004). Drosophila epsin mediates a select endocytic pathway the DSL ligands must enter to activate Notch.
  12. (2006). Drosophila melanogaster auxilin regulates the internalization of Delta to control activity of the Notch signaling pathway.
  13. (2001). Drosophila Neuralized is a ubiquitin ligase that promotes the internalization and degradation of Delta.
  14. (2007). DSL ligand endocytosis physically dissociates Notch1 heterodimers before activating proteolysis can occur.
  15. (2009). Embryonic arrest at midgestation and disruption of Notch signaling produced by the absence of both epsin 1 and epsin 2 in mice.
  16. (2010). Endocytic internalization routes required for Delta/ Notch signaling.
  17. (2009). Endocytic regulation of Notch signaling during development.
  18. (2008). Endosomal entry regulates Notch receptor activation in Drosophila melanogaster
  19. (1998). Epsin is an EHdomain-binding protein implicated in clathrin-mediated endocytosis.
  20. (2007). Epsin: inducing membrane curvature.
  21. (2004). Fat facets and Liquid facets promote Delta endocytosis and Delta signaling in the signaling cells.
  22. (1999). Frizzled regulation of Notch signaling polarizes cell fate in the Drosophila eye.
  23. (2007). Identification of genes that interact with Drosophila liquid facets.
  24. (2009). Interaction with Notch determines endocytosis of specific Delta ligands in zebrafish neural tissue.
  25. (1995). Ligand endocytosis drives receptor dissociation and activation in the Notch pathway.
  26. (2003). Mind bomb is a ubiquitin ligase that is essential for efficient activation of Notch signaling by Delta.
  27. (2007). Multiple roles of auxilin and Hsc70 in clathrinmediated endocytosis.
  28. (2001). Neuralized functions as an E3 ubiquitin ligase during Drosophila development.
  29. (2010). Neuralized promotes basal to apical transcytosis of Delta in epithelial cells.
  30. (2007). Notch signaling – constantly on the move.
  31. (2006). Notch signaling: a simple pathway becomes complex.
  32. (2009). Notch signaling: the core pathway and its posttranslational regulation.
  33. (2009). Pattern formation in the Drosophila eye disc.
  34. (2007). Pattern formation in the Drosophila eye.
  35. (1993). Pattern formation in the Drosophila retina.
  36. (1996). Proneural function of neurogenic genes in the developing Drosophila eye.
  37. (2009). Rab GTPases as coordinators of vesicle traffic.
  38. (2005). Rab11 is required during Drosophila eye development.
  39. (2005). Rab11 mediates post-Golgi trafficking of rhodopsin to the photosensitive apical membrane of Drosophila photoreceptors.
  40. (2006). Regulation of Notch signaling by endocytosis and endosomal sorting.
  41. (2005). Sec15, a component of the exocyst, promotes Notch signaling during the saymmetric division of Drosophila sensory organ precursors.
  42. (1997). Secreted forms of Delta and Serrate define antagonists of Notch signaling in Drosophila.
  43. (2007). Structural basis for autoinhibition of Notch.
  44. (2009). The Arp2/3 complex and WASp are required for apical trafficking of Delta into microvilli during cell fate specification of sensory organ precursors.
  45. (2005). The association of epsin with ubiquitinated cargo along the endocytic pathway is negatively regulated by its interaction with clathrin.
  46. (2000). The auxilin-like phosphoprotein Swa2p is required for clathrin function in yeast.
  47. (2008). The clathrin-binding motif and the Jdomain of Drosophila auxilin are essential for facilitating Notch ligand endocytosis.
  48. (2010). The endocytic matrix.
  49. (1992). The fat facets gene is required for Drosophila eye and embryo development.
  50. (2000). The function of the Drosophila Fat facets deubiquitinating enzyme in limiting photoreceptor cell number is intimately associated with endocytosis.
  51. (2005). The interplay between DSL proteins and ubiquitin ligases in Notch signaling.
  52. (2008). The intracellular region of Notch ligands
  53. (2005). The roles of receptor and ligand endocytosis in regulating Notch signaling.
  54. (2005). The ubiquitin ligase Drosophila Mindbomb promotes Notch signaling by regulating the localization and activity of Serrate and Delta.
  55. (2005). Two distinct E3 ubiquitin ligases have complementary function in the regulation of Delta and Serrate signaling in Drosophila.
  56. (1996). Undifferentiated cells in the developing Drosophila eye influence facet assembly and require the Fat facets deubiquitinating enzyme.
  57. (2006). Why is Delta endocytosis required for effective activation of Notch?
  58. (2001). Xenopus Neuralized is a ubiquitin ligase that interacts with XDelta1 and regulates Notch signaling. Dev Cell 1: 795–806. Notch Ligand Endocytosis Not Mainly for Recycling PLoS