title: Mechanisms for the maintenance and eventual degradation of neurofilament proteins in the distal segments of severed goldfish mauthner axons.
abstract: Cellular mechanisms that might affect the degradation of neurofilament proteins (NFPs) were examined in the distal segments of severed goldfish Mauthner axons (M-axons), which do not degenerate for more than 2 months after severance. Calpain levels, as determined by reactivity to a polyclonal antibody, remained constant for 80 d postseverance in distal segments of M-axons and then declined from 80 to 85 d postseverance. Calpain activity in rat brain, as determined by a spectrophotometric assay, was much higher than calpain activity in control and severed goldfish brain, spinal cord, muscle, or M-axons. Calpain activity was extremely low in M-axons compared with that in all other tissues and remained low for up to 80 d postseverance in distal segments of M-axons. Phosphorylated NFPs, as determined by Stains-All treatment of SDS gels, were maintained for up to 72 d postseverance and then decreased noticeably at 75 d postseverance when NFP breakdown products appeared on silver-stained gels. By 85 d post-severance, phosphorylated NFPs no longer were detected, and NFP breakdown products were the most prominent bands on silver-stained gels. These results suggest that the distal segments of M-axons survive for months after severance, because NFPs are maintained in a phosphorylated state that stabilizes and protects NFPs from degradation by low levels of calpain activity in the M-axon; the distal segments of severed M-axons degenerate eventually when NFPs no longer are maintained in a phosphorylated state and become susceptible to degradation, possibly by low levels of calpain activity in the M-axon.
authors.affiliation: Department of Zoology, University of Texas at Austin 78712-1064, USA.
authors.forename: T D
authors.initials: TD
authors.lastname: Raabe
authors.forename: T
authors.initials: T
authors.lastname: Nguyen
authors.forename: C
authors.initials: C
authors.lastname: Archer
authors.forename: G D
authors.initials: GD
authors.lastname: Bittner
mesh_terms: D000818:Animals; D001369:Axons / Q000378:metabolism*; D002154:Calpain / Q000378:metabolism; D003714:Denervation; D006054:Goldfish; D009419:Nerve Tissue Proteins / Q000378:metabolism; D016900:Neurofilament Proteins / Q000378:metabolism*; D010766:Phosphorylation; D013997:Time Factors; D014018:Tissue Distribution
chemical_list: D009419:Nerve Tissue Proteins; D016900:Neurofilament Proteins; D002154:Calpain