Phosphorylation of highly conserved neurofilament medium KSP repeats is not required for myelin-dependent radial axonal growth.
Neurofilament medium (NF-M) is essential for the acquisition of normal axonal caliber in response to a myelin-dependent "outside-in" trigger for radial axonal growth. Removal of the tail domain and lysine-serine-proline (KSP) repeats of NF-M, but not neurofilament heavy, produced axons with impaired radial growth and reduced conduction velocities. These earlier findings supported myelin-dependent phosphorylation of NF-M KSP repeats as an essential component of axonal growth. As a direct test of whether phosphorylation of NF-M KSP repeats is the target for the myelin-derived signal, gene replacement has now been used to produce mice in which all serines of NF-M's KSP repeats have been replaced with phosphorylation-incompetent alanines. This substitution did not alter accumulation of the neurofilaments or their subunits. Axonal caliber and motor neuron conduction velocity of mice expressing KSP phospho-incompetent NF-M were also indistinguishable from wild-type mice. Thus, phosphorylation of NF-M KSP repeats is not an essential component for the acquisition of normal axonal caliber mediated by myelin-dependent outside-in signaling.
Garcia
Michael L
ML
Department of Biological Sciences, Bond Life Sciences Center, University of Missouri-Columbia, Columbia, Missouri 65211, USA.
Rao
Mala V
MV
Fujimoto
Jiro
J
Garcia
Virginia B
VB
Shah
Sameer B
SB
Crum
John
J
Gotow
Takahiro
T
Uchiyama
Yasuo
Y
Ellisman
Mark
M
Calcutt
Nigel A
NA
Cleveland
Don W
DW
D000409:Alanine / Q000235:genetics; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution / Q000235:genetics; D000818:Animals; D001369:Axons / Q000378:metabolism / Q000502:physiology* / Q000648:ultrastructure; D017124:Conserved Sequence / Q000235:genetics; D055879:Gene Knock-In Techniques; D008239:Lysine / Q000378:metabolism; D051379:Mice; D008818:Mice, Neurologic Mutants; D008969:Molecular Sequence Data; D009186:Myelin Sheath / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D009409:Nerve Crush; D009434:Neural Pathways / Q000502:physiology; D016900:Neurofilament Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D010766:Phosphorylation / Q000235:genetics; D011392:Proline / Q000378:metabolism; D020449:Repetitive Sequences, Amino Acid / Q000235:genetics; D012694:Serine / Q000235:genetics
D016900:Neurofilament Proteins; C061195:neurofilament protein M; D012694:Serine; D011392:Proline; D008239:Lysine; D000409:Alanine