title: A Cul-3-BTB ubiquitylation pathway regulates junctional levels and asymmetry of core planar polarity proteins.
abstract: The asymmetric localisation of core planar polarity proteins at apicolateral junctions is required to specify cell polarity in the plane of epithelia. This asymmetric distribution of the core proteins is proposed to require amplification of an initial asymmetry by feedback loops. In addition, generation of asymmetry appears to require the regulation of core protein levels, but the importance of such regulation and the underlying mechanisms is unknown. Here we show that ubiquitylation acts through more than one mechanism to control core protein levels in Drosophila, and that without this regulation cellular asymmetry is compromised. Levels of Dishevelled at junctions are regulated by a Cullin-3-Diablo/Kelch ubiquitin ligase complex, the activity of which is most likely controlled by neddylation. Furthermore, activity of the deubiquitylating enzyme Fat facets is required to maintain Flamingo levels at junctions. Notably, ubiquitylation does not alter the total cellular levels of Dishevelled or Flamingo, but only that of the junctional population. When junctional core protein levels are either increased or decreased by disruption of the ubiquitylation machinery, their asymmetric localisation is reduced and this leads to disruption of planar polarity at the tissue level. Loss of asymmetry by altered core protein levels can be explained by reference to feedback models for amplification of asymmetry.
authors.affiliation: Department of Biomedical Science, University of Sheffield, Western Bank, Sheffield S10 2TN, UK. d.strutt@sheffield.ac.uk
authors.forename: Helen
authors.initials: H
authors.lastname: Strutt
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Searle
authors.forename: Victoria
authors.initials: V
authors.lastname: Thomas-Macarthur
authors.forename: Rosalind
authors.initials: R
authors.lastname: Brookfield
authors.forename: David
authors.initials: D
authors.lastname: Strutt
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism; D000818:Animals; D015153:Blotting, Western; D015820:Cadherins / Q000378:metabolism; D016764:Cell Polarity / Q000502:physiology*; D044842:Cullin Proteins / Q000378:metabolism*; D000072261:Dishevelled Proteins; D004330:Drosophila; D029721:Drosophila Proteins / Q000378:metabolism*; D010450:Endopeptidases / Q000378:metabolism; D004847:Epithelial Cells / Q000502:physiology*; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D007365:Intercellular Junctions / Q000502:physiology*; D010750:Phosphoproteins / Q000378:metabolism; D034622:RNA Interference; D015398:Signal Transduction / Q000502:physiology*; D054875:Ubiquitination / Q000502:physiology*
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D015820:Cadherins; C503647:Cul3 protein, Drosophila; D044842:Cullin Proteins; D000072261:Dishevelled Proteins; D029721:Drosophila Proteins; D010750:Phosphoproteins; C000606588:dsh protein, Drosophila; C485184:enhanced green fluorescent protein; C121420:stan protein, Drosophila; D049452:Green Fluorescent Proteins; D010450:Endopeptidases; C059237:ubiquitin-Nalpha-protein hydrolase