Vertebrate Fidgetin Restrains Axonal Growth by Severing Labile Domains of Microtubules.
Bottom Line: In Drosophila, fidgetin behaves in this fashion, with targeted knockdown resulting in neurons with a higher fraction of acetylated (stable) MT mass in their axons.Concomitantly, there are more minor processes and a longer axon.Together with experimental data showing that vertebrate fidgetin targets unacetylated tubulin, these results indicate that vertebrate fidgetin (unlike its fly ortholog) regulates neuronal development by tamping back the expansion of the labile domains of MTs.
Affiliation: Department of Neurobiology and Anatomy, Drexel University College of Medicine, Philadelphia, PA 19129, USA.Show MeSH
Related in: MedlinePlus
Mentions: The effects of knocking down Drosophila Fgn from fly neurons in the neuromuscular junction (NMJ) were investigated first. The Gal4/UAS system (Brand and Perrimon, 1993) was used to express an RNAi hairpin targeting the Drosophila Fgn gene (CG3326, or Fgn) under UAS control (UAS:Fgn-RNAi). Expression was limited to post-mitotic neurons using the Elav-gal4 driver (Campos et al., 1987). The total number of synaptic contacts (boutons) was significantly higher in Fgn-knockdown animals (Figures 1B and 1E) compared to outcrossed control (Ctl) animals (Figures 1A and 1E). The number of satellite boutons, which are small growths of presynaptic membranes that extend out from axonal terminal arbors, in Fgn-knockdown animals (arrows in Figures 1D and 1E) was greater than that of Ctls (Figures 1C and 1E). An increased number of satellite boutons has been observed in flies bearing mutations to other MT-severing proteins (Sherwood et al., 2004; Mao et al., 2014). A significant increase in the ratio of acetylated to total tubulin (measured by quantifying fluorescence intensity) was observed in the axonal shaft and distal synapse, compared to two independent control RNAi lines (Ctl1 and Ctl2) (Figure 1F). This was due to a significant increase in MT acetylation in these areas, as total tubulin levels remained relatively unchanged (Figure 1F). A similar result has been reported in Drosophila neurons with compromised katanin (Mao et al., 2014). These results are consistent with Drosophila Fgn behaving similarly to traditional MT-severing proteins in the neurons of the fly.
Affiliation: Department of Neurobiology and Anatomy, Drexel University College of Medicine, Philadelphia, PA 19129, USA.