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Table 1.

In vivo experiments supporting a role for morphogens in axon guidance

Morphogen pathwaysGenesSpeciesExperimentsPhenotypesReferences
Hedgehog Smo Mouse Conditional inactivation of Smo in commissural neurons Commissural axons invade the motor columns Charron et al., 2003  
 Shh Chick Ectopic expression of Shh in the optic chiasm Retinal axons are prevented from crossing the chiasm Trousse et al., 2001  
 Shh Chick Silencing of Shh by RNA interference Commissural axons stall at the contraiateral floor plate border, with some axons randomly turning caudally or rostrally Bourikas et al., 2005  
TGFβ/BMP Bmp7 and Gdf7 Mouse Bmp7 and Gdf7 gene inactivation Initial trajectory of commissural axons aberrant, axons invade the roof plate Augsburger et al., 1999; Butler and Dodd, 2003  
 unc-129 C. elegans unc-129 mutation Defects in the dorsally oriented trajectories of motor axons Colavita and Culotti, 1998; Colavita et al., 1998  
Wnt drl Drosophila drl mutation Axons that normally project into the anterior commissure now project into the posterior commissure Bonkowsky et al., 1999  
 drl Drosophila Ectopic expression of Drl in posterior commissure neurons Forces posterior commissure neurons to cross in the anterior commissure Bonkowsky et al., 1999  
 wnt5 Drosophila wnt5 mutation Axons that normally project into the anterior commissure project into the posterior commissure Yoshikawa et al., 2003  
 wnt5 Drosophila Ectopic expression of Wnt5 throughout the CNS midline Prevents the anterior commissure from forming Yoshikawa et al., 2003  
 Fz3 Mouse Fz3 gene inactivation Defects in anteroposterior guidance of commissural axons after midline crossing Lyuksyutova et al., 2003  
Morphogen pathwaysGenesSpeciesExperimentsPhenotypesReferences
Hedgehog Smo Mouse Conditional inactivation of Smo in commissural neurons Commissural axons invade the motor columns Charron et al., 2003  
 Shh Chick Ectopic expression of Shh in the optic chiasm Retinal axons are prevented from crossing the chiasm Trousse et al., 2001  
 Shh Chick Silencing of Shh by RNA interference Commissural axons stall at the contraiateral floor plate border, with some axons randomly turning caudally or rostrally Bourikas et al., 2005  
TGFβ/BMP Bmp7 and Gdf7 Mouse Bmp7 and Gdf7 gene inactivation Initial trajectory of commissural axons aberrant, axons invade the roof plate Augsburger et al., 1999; Butler and Dodd, 2003  
 unc-129 C. elegans unc-129 mutation Defects in the dorsally oriented trajectories of motor axons Colavita and Culotti, 1998; Colavita et al., 1998  
Wnt drl Drosophila drl mutation Axons that normally project into the anterior commissure now project into the posterior commissure Bonkowsky et al., 1999  
 drl Drosophila Ectopic expression of Drl in posterior commissure neurons Forces posterior commissure neurons to cross in the anterior commissure Bonkowsky et al., 1999  
 wnt5 Drosophila wnt5 mutation Axons that normally project into the anterior commissure project into the posterior commissure Yoshikawa et al., 2003  
 wnt5 Drosophila Ectopic expression of Wnt5 throughout the CNS midline Prevents the anterior commissure from forming Yoshikawa et al., 2003  
 Fz3 Mouse Fz3 gene inactivation Defects in anteroposterior guidance of commissural axons after midline crossing Lyuksyutova et al., 2003  
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