A wave-based mechanism to connect two distinct cytoskeletons in neurons

  Yu-Hsuan Lin(林彧亘)1, Yuang-An Huang1, Chih-Hsuan Hsu2 ,Eric Hwang1,2,3,4

   1. Dept Biol Sci and Technol, Nat’l Yang Ming Chiao Tung Univ, Hsinchu, Taiwan

   2. Inst Mol Med and Bioeng, Nat’l Yang Ming Chiao Tung Univ, Hsinchu, Taiwan

   3. Inst Bioinform and Syst Biol, Nat’l Yang Ming Chiao Tung Univ, Hsinchu, Taiwan

   4. Center for Intell Drug Syst and Smart Bio-devices, Nat’l Yang Ming Chiao Tung Univ, Hsinchu, Taiwan

Microtubule (MT) and actin are vital components of the cytoskeleton in neurons, playing important roles in morphogenesis, motility, and connectivity. While MT-organizing centers (MTOCs) are typically located in the centrosome of mitotic cells,  non-centrosomal MTOCs exist in post-mitotic neurons that contribute to MT formation and organization. We have shown that one important location of active non-centrosomal MTOCs is at the tip of the neurite. Targeting protein for Xklp2 (TPX2) plays an important role in the organization of MTs at these non-centrosomal MTOCs: it can associate with existing MTs to promote the nucleation of new one. However, TPX2 is normally bound by the importin α/β heterodimer, and its activity is inhibited. GTP-bound Ran (RanGTP) binds to importin-β, and releases TPX2 from the inhibitory importin heterodimer, allowing TPX2 to initiate MT nucleation. Our previous research has shown that actin waves transport RanGTP from the cell body to the tips of neurites and promote the formation of non-centrosomal MTs. This demonstrates a functional interplay between the MT and actin cytoskeleton to facilitate MT formation at the tip of the neurite. However, the specific adapter protein linking actin waves and RanGTP is still unknown. Through co-immunoprecipitation and quantitative mass spectrometry, we identified numerous neuronal proteins that have a higher affinity toward RanGTP than RanGDP. We then screened for proteins associated with actin waves, which resulted in a handful of candidate proteins, one of which was the small G-protein RhoA. We are investigating the possibility that RhoA acts as an adapter protein linking RanGTP to actin waves. We will present data examining the effects of RhoA phosphorylation mutations and PKA inhibitors/activators on the enrichment of RanGTP at neurite tips.