Differential dynamics of neurofilament-H protein and neurofilament-L protein in neurons.
Neurofilaments (NFs) are composed of triplet proteins, NF-H, NF-M, and NF-L. To understand the dynamics of NFs in vivo, we studied the dynamics of NF-H and compared them to those of NF-L, using the combination of microinjection technique and fluorescence recovery after photobleaching. In the case of NF-L protein, the bleached zone gradually restored its fluorescence intensity with a recovery half time of approximately 35 min. On the other hand, recovery of the bleached zone of NF-H was considerably faster, taking place in approximately 19 min. However, in both cases the bleached zone was stationary. Thus, it was suggested that NF-H is the dynamic component of the NF array and is interchangeable, but that it assembles with the other neurofilament triplet proteins in a more exchangeable way, implying that the location of NF-H is in the periphery of the core NF array mainly composed of NF-L subunits. Immunoelectron microscopy investigations of the incorporation sites of NF-H labeled with biotin compounds also revealed the lateral insertion of NF-H subunits into the preexisting NF array, taking after the pattern seen in the case of NF-L. In summary, our results demonstrate that the dynamics of the L and H subunit proteins in situ are quite different from each other, suggesting different and separated mechanisms or structural specialization underlying the behavior of the two proteins.
Takeda
S
S
Department of Anatomy and Cell Biology, Faculty of Medicine, University of Tokyo, Japan.
Okabe
S
S
Funakoshi
T
T
Hirokawa
N
N
D000818:Animals; D001369:Axons / Q000378:metabolism; D002417:Cattle; D002478:Cells, Cultured; D005727:Ganglia, Spinal / Q000166:cytology; D051379:Mice; D008845:Microinjections; D008856:Microscopy, Fluorescence / Q000379:methods; D016253:Microscopy, Immunoelectron; D016900:Neurofilament Proteins / Q000378:metabolism* / Q000648:ultrastructure; D009475:Neurons, Afferent / Q000378:metabolism*; D010777:Photochemistry
D016900:Neurofilament Proteins; C044882:neurofilament protein L; C051774:neurofilament protein H