The ubiquitin ligase Phr1 regulates axon outgrowth through modulation of microtubule dynamics

Neuron. 2007 Nov 21;56(4):604-20. doi: 10.1016/j.neuron.2007.09.009.


To discover new genes involved in axon navigation, we conducted a forward genetic screen for recessive alleles affecting motor neuron pathfinding in GFP reporter mice mutagenized with ENU. In Magellan mutant embryos, motor axons were error prone and wandered inefficiently at choice points within embryos, but paradoxically responded to guidance cues with normal sensitivity in vitro. We mapped the Magellan mutation to the Phr1 gene encoding a large multidomain E3 ubiquitin ligase. Phr1 is associated with the microtubule cytoskeleton within neurons and selectively localizes to axons but is excluded from growth cones. Motor and sensory neurons from Magellan mutants display abnormal morphologies due to a breakdown in the polarized distribution of components that segregate between axons and growth cones. The Magellan phenotype can be reversed by stabilizing microtubules with taxol or inhibiting p38MAPK activity. Thus, efficacious pathfinding requires Phr1 activity for coordinating the cytoskeletal organization that distinguishes axons from growth cones.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cell Differentiation / genetics
  • Cells, Cultured
  • Efferent Pathways / abnormalities
  • Efferent Pathways / cytology
  • Efferent Pathways / metabolism
  • Enzyme Inhibitors / pharmacology
  • Gene Expression Regulation, Developmental / genetics
  • Genetic Testing
  • Growth Cones / metabolism*
  • Growth Cones / ultrastructure
  • MAP Kinase Signaling System / drug effects
  • MAP Kinase Signaling System / genetics
  • Male
  • Mice
  • Mice, Inbred C57BL
  • Mice, Inbred DBA
  • Mice, Transgenic
  • Microtubules / metabolism*
  • Microtubules / ultrastructure
  • Motor Neurons / cytology
  • Motor Neurons / metabolism*
  • Mutation / genetics
  • Paclitaxel / pharmacology
  • Spinal Cord / abnormalities*
  • Spinal Cord / cytology
  • Spinal Cord / metabolism*
  • Tubulin Modulators / pharmacology
  • p38 Mitogen-Activated Protein Kinases / antagonists & inhibitors
  • p38 Mitogen-Activated Protein Kinases / metabolism
  • ral Guanine Nucleotide Exchange Factor / genetics
  • ral Guanine Nucleotide Exchange Factor / metabolism*


  • Enzyme Inhibitors
  • Rgl3 protein, mouse
  • Tubulin Modulators
  • ral Guanine Nucleotide Exchange Factor
  • p38 Mitogen-Activated Protein Kinases
  • Paclitaxel