DFsn collaborates with Highwire to down-regulate the Wallenda/DLK kinase and restrain synaptic terminal growth.
BACKGROUND
The growth of new synapses shapes the initial formation and subsequent rearrangement of neural circuitry. Genetic studies have demonstrated that the ubiquitin ligase Highwire restrains synaptic terminal growth by down-regulating the MAP kinase kinase kinase Wallenda/dual leucine zipper kinase (DLK). To investigate the mechanism of Highwire action, we have identified DFsn as a binding partner of Highwire and characterized the roles of DFsn in synapse development, synaptic transmission, and the regulation of Wallenda/DLK kinase abundance.


RESULTS
We identified DFsn as an F-box protein that binds to the RING-domain ubiquitin ligase Highwire and that can localize to the Drosophila neuromuscular junction. Loss-of-function mutants for DFsn have a phenotype that is very similar to highwire mutants - there is a dramatic overgrowth of synaptic termini, with a large increase in the number of synaptic boutons and branches. In addition, synaptic transmission is impaired in DFsn mutants. Genetic interactions between DFsn and highwire mutants indicate that DFsn and Highwire collaborate to restrain synaptic terminal growth. Finally, DFsn regulates the levels of the Wallenda/DLK kinase, and wallenda is necessary for DFsn-dependent synaptic terminal overgrowth.


CONCLUSIONS
The F-box protein DFsn binds the ubiquitin ligase Highwire and is required to down-regulate the levels of the Wallenda/DLK kinase and restrain synaptic terminal growth. We propose that DFsn and Highwire participate in an evolutionarily conserved ubiquitin ligase complex whose substrates regulate the structure and function of synapses.
Wu
Chunlai
C
Department of Molecular Biology and Pharmacology, Washington University School of Medicine, St. Louis, MO 63110, USA. cwu@wustl.edu
Daniels
Richard W
RW
DiAntonio
Aaron
A
D000818:Animals; D029742:Caenorhabditis elegans Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D002454:Cell Differentiation / Q000235:genetics*; D017124:Conserved Sequence; D015536:Down-Regulation / Q000235:genetics; D029721:Drosophila Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D004331:Drosophila melanogaster; D019143:Evolution, Molecular; D044783:F-Box Proteins / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D006131:Growth Inhibitors / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D020930:MAP Kinase Kinase Kinases / Q000235:genetics / Q000378:metabolism*; D009154:Mutation / Q000235:genetics; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D009420:Nervous System / Q000166:cytology / Q000378:metabolism*; D009469:Neuromuscular Junction / Q000196:embryology / Q000235:genetics / Q000378:metabolism; D017729:Presynaptic Terminals / Q000378:metabolism / Q000648:ultrastructure; D043743:Ubiquitin-Protein Ligase Complexes / Q000235:genetics / Q000378:metabolism
D029742:Caenorhabditis elegans Proteins; D029721:Drosophila Proteins; D044783:F-Box Proteins; C530278:FSN-1 protein, C elegans; C533256:Fsn protein, Drosophila; D006131:Growth Inhibitors; C409633:HIW protein, Drosophila; D009419:Nerve Tissue Proteins; D043743:Ubiquitin-Protein Ligase Complexes; D020930:MAP Kinase Kinase Kinases; C512899:wnd protein, Drosophila
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