Disruption of type IV intermediate filament network in mice lacking the neurofilament medium and heavy subunits

Citation
H. Jacomy et al., Disruption of type IV intermediate filament network in mice lacking the neurofilament medium and heavy subunits, J NEUROCHEM, 73(3), 1999, pp. 972-984
Citations number
54
Categorie Soggetti
Neurosciences & Behavoir
Journal title
JOURNAL OF NEUROCHEMISTRY
ISSN journal
00223042 → ACNP
Volume
73
Issue
3
Year of publication
1999
Pages
972 - 984
Database
ISI
SICI code
0022-3042(199909)73:3<972:DOTIIF>2.0.ZU;2-N
Abstract
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 re duction 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 twofold, whereas the steady-stale levels of assembl ed NF-L were reduced. Although the NF-M or NF-H subunits are each dispensab le for the formation of intermediate filaments, the absence of both subunit s in double NF-M; NF-H knockout mice led to a scarcity of intermediate fila ment structures in axons and to a marked approximately twofold increase in the number of microtubules. Protein analysis indicated that the levels of N F-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 b ut a weak NF-L staining in axons. In addition, axonal transport studies car ried out by the injection of [S-35]methionine into spinal cord revealed aft er 30 days very low levels of newly synthesized NF-L proteins in the sciati c nerve of NF-M-/-;NF-H-/- mice. The combined results demonstrate a require ment of the high-molecular-weight subunits for the assembly of type IV inte rmediate filament proteins and for the efficient translocation of NF-L prot eins into the axonal compartment.