Journal of Neuroscience, Vol 8, 4797-4808, Copyright © 1988 by Society for Neuroscience
Expression of two developmentally regulated brain-specific proteins is correlated with late outgrowth of the pyramidal tract
K Kalil and M Perdew
Department of Anatomy, University of Wisconsin, Madison 53706.
The regulation of axon outgrowth is not well understood. In previous
studies, however, axon elongation has been well correlated with expression
of a small number of growth-associated proteins (GAPs). To identify other
proteins whose expression could be correlated with axon outgrowth during
development of CNS pathways, monoclonal antibodies were raised against
growth cone particles isolated from neonatal hamster brains. Two of these
antibodies recognized a brain-specific 33 kDa protein associated with
intracellular membranes of axons and growth cones. Immunoblotting
demonstrated a sharp developmental decline in levels of the protein in
hamster brain during the first postnatal week and a more gradual decline
thereafter. Immunocytochemical studies with the antibodies revealed
ubiquitous staining of the neuropil during the first several days, which by
the end of the first week became restricted to a few later-maturing
pathways. Staining was most intense in the pyramidal tract and was well
correlated with axon outgrowth, which continues until 14 d in this pathway.
These results suggest that the 33 kDa protein may, like previously
identified GAPs, play a role in axon elongation. Late outgrowth of the
hamster pyramidal tract is also correlated with expression of another
developmentally regulated protein, the high-molecular-weight neurofilament
subunit (NF-H). Immunostaining with a monoclonal antibody that recognized
phosphorylated NF-H demonstrated that this subunit does not begin to appear
in the late-maturing pyramidal tract fibers until several weeks after
birth, in striking contrast to intense immunoreactivity of other spinal
cord pathways from postnatal day 1. This finding suggests that specific
pathways may have a highly idiosyncratic time course for expression of
neurofilament subunits.