Disruption of the NF-H gene increases axonal microtubule content and velocity of neurofilament transport: relief of axonopathy resulting from the toxin beta,beta'-iminodipropionitrile.
To investigate the role of the neurofilament heavy (NF-H) subunit in neuronal function, we generated mice bearing a targeted disruption of the gene coding for the NF-H subunit. Surprisingly, the lack of NF-H subunits had little effect on axonal calibers and electron microscopy revealed no significant changes in the number and packing density of neurofilaments made up of only the neurofilament light (NF-L) and neurofilament medium (NF-M) subunits. However, our analysis of NF-H knockout mice revealed an approximately 2.4-fold increase of microtubule density in their large ventral root axons. This finding was further corroborated by a corresponding increase in the ratio of assembled tubulin to NF-L protein in insoluble cytoskeletal preparations from the sciatic nerve. Axonal transport studies carried out by the injection of [35S]methionine into spinal cord revealed an increased transport velocity of newly synthesized NF-L and NF-M proteins in motor axons of NF-H knockout mice. When treated with beta,beta'-iminodipropionitrile (IDPN), a neurotoxin that segregates microtubules and retards neurofilament transport, mice heterozygous or homozygous for the NF-H null mutation did not develop neurofilamentous swellings in motor neurons, unlike normal mouse littermates. These results indicate that the NF-H subunit is a key mediator of IDPN-induced axonopathy.
Centre for Research in Neuroscience, McGill University, The Montreal General Hospital Research Institute, Montréal, Qúebec, Canada H3G 1A4.
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Q
Zhu
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Lindenbaum
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Levavasseur
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H
Jacomy
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JP
Julien
D008841:Actin Cytoskeleton / Q000502:physiology / Q000648:ultrastructure; D000818:Animals; D001369:Axons / Q000187:drug effects / Q000502:physiology* / Q000648:ultrastructure; D005091:Exons; D005727:Ganglia, Spinal / Q000502:physiology* / Q000648:ultrastructure; D051379:Mice; D018345:Mice, Knockout; D008870:Microtubules / Q000502:physiology* / Q000648:ultrastructure; D009413:Nerve Fibers, Myelinated / Q000502:physiology* / Q000648:ultrastructure; D016900:Neurofilament Proteins / Q000172:deficiency / Q000235:genetics* / Q000502:physiology*; D009498:Neurotoxins / Q000633:toxicity*; D009570:Nitriles / Q000633:toxicity*
D016900:Neurofilament Proteins; D009498:Neurotoxins; D009570:Nitriles; C044882:neurofilament protein L; C051774:neurofilament protein H; C061195:neurofilament protein M; C008110:3,3'-iminodipropionitrile