Disruption of type IV intermediate filament network in mice lacking the neurofilament medium and heavy subunits.
To clarify the role of the neurofilament (NF) medium (NF-M) and heavy (NF-H) subunits, we generated mice with targeted disruption of both NF-M and NF-H genes. The absence of the NF-M subunit resulted in a two- to threefold reduction in the caliber of large myelinated axons, whereas the lack of NF-H subunits had little effect on the radial growth of motor axons. In NF-M-/- mice, the velocity of axonal transport of NF light (NF-L) and NF-H proteins was increased by about two-fold, whereas the steady-state levels of assembled NF-L were reduced. Although the NF-M or NF-H subunits are each dispensable for the formation of intermediate filaments, the absence of both subunits in double NF-M; NF-H knockout mice led to a scarcity of intermediate filament structures in axons and to a marked approximately twofold increase in the number of microtubules. Protein analysis indicated that the levels of NF-L and alpha-internexin proteins were reduced dramatically throughout the nervous system. Immunohistochemistry of spinal cord from the NF-M-/-;NF-H-/- mice revealed enhanced NF-L staining in the perikaryon of motor neurons but a weak NF-L staining in axons. In addition, axonal transport studies carried out by the injection of [35S]methionine into spinal cord revealed after 30 days very low levels of newly synthesized NF-L proteins in the sciatic nerve of NF-M-/-;NF-H-/- mice. The combined results demonstrate a requirement of the high-molecular-weight subunits for the assembly of type IV intermediate filament proteins and for the efficient translocation of NF-L proteins into the axonal compartment.
Jacomy
H
H
Montreal General Hospital Research Institute, Québec, Canada.
Zhu
Q
Q
Couillard-Després
S
S
Beaulieu
J M
JM
Julien
J P
JP
D000818:Animals; D001369:Axons / Q000502:physiology; D002352:Carrier Proteins / Q000096:biosynthesis / Q000235:genetics; D004591:Electrophoresis, Polyacrylamide Gel; D015151:Immunoblotting; D007150:Immunohistochemistry; D007381:Intermediate Filament Proteins / Q000235:genetics / Q000502:physiology*; D051379:Mice; D018345:Mice, Knockout; D008854:Microscopy, Electron; D008970:Molecular Weight; D016900:Neurofilament Proteins / Q000737:chemistry / Q000172:deficiency* / Q000235:genetics / Q000378:metabolism; D012313:RNA / Q000032:analysis / Q000235:genetics
D002352:Carrier Proteins; D007381:Intermediate Filament Proteins; D016900:Neurofilament Proteins; C046643:alpha-internexin; C044882:neurofilament protein L; C051774:neurofilament protein H; C061195:neurofilament protein M; D012313:RNA