Conditional NF-L transgene expression in mice for in vivo analysis of turnover and transport rate of neurofilaments.
We generated mice with doxycycline control of a human neurofilament light (NF-L) transgene in the context of the absence (tTA;hNF-L;NF-L(-/-)) or presence (tTA;hNF-L;NF-L(+/-)) of endogenous mouse NF-L proteins. Doxycycline treatment caused the rapid disappearance of human NF-L (hNF-L) mRNA in tTA;hNF-L mice, but the hNF-L proteins remained with a half-life of 3 weeks in the brain. In the sciatic nerve, the disappearance of hNF-L proteins after doxycycline treatment occurred in synchrony along the sciatic nerve, suggesting a proteolysis of NF proteins along the entire axon. The presence of permanent NF network in tTA;hNF-L;NF-L(+/-) mice further stabilized and extended longevity of hNF-L proteins by several months. Surprisingly, after cessation of doxycycline treatment, there was no evidence of leading front of newly synthesized hNF-L proteins migrating into sciatic nerve axons devoid of NF structures. The hNF-L proteins detected at weekly intervals reappeared and accumulated in synchrony at similar rate along nerve segments, a phenomenon consistent with a fast hNF-L transport into axons. We estimated the hNF-L transport rate to be of approximately 10 mm/d in axons devoid of NF structures based on the use of an adenovirus encoding tet-responsive transcriptional activator to transactivate the hNF-L transgene in hypoglossal motor neurons. These results provide in vivo evidence that the stationary NF network in axons is a key determinant of half-life and transport rate of NF proteins.
Millecamps
Stéphanie
S
Centre de Recherche du Centre Hospitalier de l'Université Laval, Department of Anatomy and Physiology of Laval University, Quebec, Canada.
Gowing
Geneviève
G
Corti
Olga
O
Mallet
Jacques
J
Julien
Jean-Pierre
JP
D000818:Animals; D001370:Axonal Transport / Q000235:genetics*; D005786:Gene Expression Regulation / Q000502:physiology*; D006207:Half-Life; D006801:Humans; D051379:Mice; D008809:Mice, Inbred C3H; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008822:Mice, Transgenic; D016900:Neurofilament Proteins / Q000096:biosynthesis* / Q000235:genetics* / Q000378:metabolism / Q000502:physiology; D021381:Protein Transport / Q000235:genetics
D016900:Neurofilament Proteins; C044882:neurofilament protein L