Zelin Jia**Phosphorylation-induced variation of NF kinetics and morphology of axon**Zelin Jia1, Yinyun Li1*1. School of Systems Science, Beijing Normal University, Beijing, 100875, China* yinyun@bnu.edu.cnAbstractNeurofilaments(NFs) are transported along microtubule tracks in the axons, and are gradually phosphorylated in this process. At the node of Ranvier, the axon is not encased by myelin sheath. It is indicated that phosphorylation of NFs can reduce the transport rate of NFs, and therefore influence the formation of axon morphology. In the theory of slow axonal transport, the “stop-and-go” model can well describe the random kinetic behavior of NFs in axons. On the basis of “stop-and-go” model, we introduce the conversion between phosphorylation and dephosphorylation of neurofilaments and build the “eight- state” model. We assume that the phosphorylation and dephosphorylation of NFs has different “on-track” rate (γon), so as to achieve the effect of phosphorylation on the transport. Through our theoretical derivation and simulation, we draw the conclusion that the modification on the “on-track” rate and the conversion between phosphorylation and dephosphorylation can both slow down the NFs transport along the axon. Our conclusion is also consistent with the Continuity equation that flux by the multiplication of the number of NFs and average velocity is constant at equilibrium state.**Key words** : axonal transport, phosphorylation, “eight-state” modelReference[1] Nixon, R(1994) Phosphorylation on carboxyl terminus domains of neurofilament proteins in retinal ganglion cell neurons in vivo: influences on regional neurofilament accumulation, interneurofilament spacing, and axon caliber. J. Cell Biol[2] Wang L and Brown, A (2001) Rapid intermittent movement of axonal neurofilaments observed by fluorescence photobleaching Mol. Biol. Cell 12 3257–67[3] Jung, C., Yabe, J.T. & Shea, T.B. (2000b) C-terminal phosphorylation of theheavy molecular weight neurofilament subunit is inversely correlated with neurofilament axonal transport velocity. Brain Res., 856, 12–19.[4] Yabe, J.T., Pimenta, A. & Shea, T.B. (1999) Kinesin-mediated transport of neurofilament protein oligomers in growing axons. J. Cell Sci., 112, 3799-3814.[5] Yabe, J.T., Chan, W. & Shea. T.B. (2000) Phospho-dependent association ofneurofilament proteins with kinesin in situ. Cell Motil. Cytoskel., 42, 230–240.
