Neurofilaments Consist of Distinct Populations That Can Be Distinguished by C-Terminal Phosphorylation, Bundling, and Axonal Transport Rate in Growing Axonal Neurites

摘要: We examined the steady-state distribution and axonal transport of neurofilament (NF) subunits within growing neurites NB2a/d1 cells. Ultrastructural analyses demonstrated a longitudinally oriented “bundle” closely apposed NFs that was surrounded by more widely spaced individual NFs. NF bundles were recovered during fractionation could be isolated from sedimentation through sucrose. Immunoreactivity toward restrictive C-terminal phospho-dependent antibody RT97 significantly prominent on bundled than Microinjected biotinylated subunits, GFP-tagged expressed after transfection, radiolabeled endogenous all associated with before they Biotinylated did not accumulate uniformly along NFs; initially appeared proximal portion bundle only subsequently observed entire length These findings demonstrate are homogeneous but, rather, consist distinct populations. One these is characterized less extensive phosphorylation relative lack NF–NF interactions. The other increased interactions either undergoes markedly slower or does turnover via subunit and/or filament exchange Inhibition phosphatase activities living collectively suggest responsible for slowing transport.