Optic Nerve Regeneration is Enhanced in Dock3 Overexpressing Transgenic Mice

1. Kazuhiko Namekata
2. Chikako Harada
3. Xiaoli Guo
4. Takayuki Harada

Tokyo Metropolitan Institute for Neuroscience, Tokyo, Japan

Purpose: Rho GTPases are required for axonal outgrowth and dendrite formation through rearrangement of actin filaments in neurons. Dock family proteins regulate Rho GTPase activity and are expressed in a variety of tissues. This study was conducted to define the role of Dock3, a neuron specific Dock family protein, in axonal outgrowth and regeneration.

Methods: Dock3 overexpressing transgenic (Tg) mice were generated using a CAG promoter. To measure axonal length in retinal explants, axons were traced and calculated after visualizing with rhodamine-phalloidin staining. Mice optic nerves were exposed intraorbitally and crushed with fine surgical forceps. Fourteen days after surgery, axonal regeneration was quantified by counting GAP43-positive axons that crossed a virtual line parallel to the lesion site. Protein levels of MAG, Nogo and OMgp in optic nerve were determined by immunoblot analysis.

Result & Conclusions: Tg mice showed high expression levels of Dock3 in many tissues, especially in the optic nerve and retina, but the structure of such tissues were normal. In retinal explant culture, the axonal length of Tg mice was greater than that of their WT littermates. In addition, adult Tg mice exhibited enhanced optic nerve regeneration after injury. The expression levels of MAG, Nogo and OMgp were not altered between WT and Tg mice. Thus, Dock3 plays a critical role in axonal outgrowth and regeneration in the adult CNS without affecting Nogo receptor-mediated inhibitory effects.