K+Channel Kv3.4 Is Essential for Axon Growth by Limiting the Influx of Ca2+into Growth Cones.
Membrane excitability in the axonal growth cones of embryonic neurons influences axon growth. Voltage-gated K+(Kv) channels are key factors in controlling membrane excitability, but whether they regulate axon growth remains unclear. Here, we report that Kv3.4 is expressed in the axonal growth cones of embryonic spinal commissural neurons, motoneurons, dorsal root ganglion neurons, retinal ganglion cells, and callosal projection neurons during axon growth. Ourin vitro(cultured dorsal spinal neurons of chick embryos) andin vivo(developing chick spinal commissural axons and rat callosal axons) findings demonstrate that knockdown of Kv3.4 by a specific shRNA impedes axon initiation, elongation, pathfinding, and fasciculation. In cultured dorsal spinal neurons, blockade of Kv3.4 by blood depressing substance II suppresses axon growth via an increase in the amplitude and frequency of Ca2+influx through T-type and L-type Ca2+channels. Electrophysiological results show that Kv3.4, the major Kv channel in the axonal growth cones of embryonic dorsal spinal neurons, is activated at more hyperpolarized potentials and inactivated more slowly than it is in postnatal and adult neurons. The opening of Kv3.4 channels effectively reduces growth cone membrane excitability, thereby limiting excessive Ca2+influx at subthreshold potentials or during Ca2+-dependent action potentials. Furthermore, excessive Ca2+influx induced by an optogenetic approach also inhibits axon growth. Our findings suggest that Kv3.4 reduces growth cone membrane excitability and maintains [Ca2+]iat an optimal concentration for normal axon growth.SIGNIFICANCE STATEMENTAccumulating evidence supports the idea that impairments in axon growth contribute to many clinical disorders, such as autism spectrum disorders, corpus callosum agenesis, Joubert syndrome, Kallmann syndrome, and horizontal gaze palsy with progressive scoliosis. Membrane excitability in the growth cone, which is mainly controlled by voltage-gated Ca2+(Cav) and K+(Kv) channels, modulates axon growth. The role of Cav channels during axon growth is well understood, but it is unclear whether Kv channels control axon outgrowth by regulating Ca2+influx. This report shows that Kv3.4, which is transiently expressed in the axonal growth cones of many types of embryonic neurons, acts to reduce excessive Ca2+influx through Cav channels and thus permits normal axon outgrowth.
Institute of Neuroscience, Brain Research Center, National Yang-Ming University, Taipei 112, Taiwan.
Chia-Yi
0000-0003-1126-6990
CY
Huang
Institute of Neuroscience, Brain Research Center, National Yang-Ming University, Taipei 112, Taiwan.
Cheng-Chang
0000-0002-6692-9942
CC
Lien
Institute of Neuroscience, Brain Research Center, National Yang-Ming University, Taipei 112, Taiwan.
Chau-Fu
CF
Cheng
Institute of Neuroscience, Brain Research Center, National Yang-Ming University, Taipei 112, Taiwan.
Ting-Yun
0000-0002-1946-5532
TY
Yen
Institute of Neuroscience, Brain Research Center, National Yang-Ming University, Taipei 112, Taiwan.
Chieh-Ju
CJ
Chen
Institute of Neuroscience, Brain Research Center, National Yang-Ming University, Taipei 112, Taiwan mltsaur@ym.edu.tw.
Meei-Ling
0000-0002-2874-5034
ML
Tsaur
D000200:Action Potentials / Q000502:physiology; D000818:Animals; D001369:Axons / Q000502:physiology*; D002118:Calcium / Q000378:metabolism*; D002642:Chick Embryo; D003337:Corpus Callosum / Q000166:cytology / Q000378:metabolism; D018274:Electroporation; D005727:Ganglia, Spinal / Q000166:cytology / Q000378:metabolism; D055785:Gene Knockdown Techniques; D020439:Growth Cones / Q000378:metabolism*; D009046:Motor Neurons / Q000378:metabolism; D009474:Neurons / Q000378:metabolism; D024642:Potassium Channels, Voltage-Gated / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D012165:Retinal Ganglion Cells / Q000378:metabolism
D024642:Potassium Channels, Voltage-Gated; D002118:Calcium
Ca2+ influx; axon growth; growth cone; membrane excitability; voltage-gated K+ channels