Neuronal polarity: establishing and maintaining the axon initial segment
Beuningen, S.F.B. van
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Neurons with their dendrites and axons have a highly polarized morphology. Axons are functionally different from dendrites, as they can generate an action potential, required for fast and consistent electric signal transfer. The axon initial segment (AIS) is a specialized region found at the beginning of the axon close to the cell body. This region is very important for the induction of the action potential. It has also been suggested to form a selective transport filter and diffusion barrier at the beginning of the axon. The AIS is therefore an important region required for maintaining neuron polarity. This thesis discusses briefly the current understanding of molecular mechanisms involved in neuron polarization, like NGF and TGF-β signalling. Both the appearance and the function of major AIS proteins, such as AnkG, NF-186, and voltage-gated sodium channels, are subsequently discussed more extensively in this thesis. These proteins play an important role in the three functions of the AIS, namely action potential generation, selective transport filter, and diffusion barrier. The question remains how the AIS is exactly build and how this relates to the induction of neuron polarization, a question which is examined in the discussion.