Journal of Neuroscience, Vol 8, 4445-4454, Copyright © 1988 by Society for Neuroscience
Changes in rapidly transported proteins in developing hamster retinofugal axons
KL Moya, LI Benowitz, S Jhaveri and GE Schneider
Department of Brain and Cognitive Sciences, Whitaker College, Massachusetts Institute of Technology, Cambridge 02139.
Proteins synthesized in retinal ganglion cells and conveyed to the
terminals of optic tract axons in the rapid phase of axonal transport were
analyzed at different developmental stages in the hamster. Animals between
2 d of age and adulthood were labeled intraocularly with 35S- methionine,
and after a 4 hr survival time, the superior colliculus was dissected out,
subjected to subcellular fractionation, and radiolabeled proteins in the
particulate fraction analyzed by 2-dimensional gel electrophoresis and
fluorography. The previously identified growth- associated phosphoprotein,
GAP-43 (GAP-48, B-50, F1, pp46), was synthesized and transported at high
levels in the neonate, but these levels declined precipitously after the
second postnatal week. Immunohistochemical studies using a monospecific
antibody showed that GAP-43 was localized along the entire length of
retinal axons in the optic tract and target areas in P2 animals but was
virtually absent in the adult visual pathway. By metabolic labeling, 2
proteins with molecular weights of about 230 kDa also showed a sharp
decrease during development. In contrast, acidic proteins of 27 and 64 kDa,
which were barely detectable in the neonate, increased steadily to become
the most heavily labeled proteins of rapid axonal transport by the second
postnatal week. Another group of proteins, of about 94-110 kDa, also rose
to peak levels after birth but then declined. Temporal correlations between
the molecular changes described here and the known anatomical events in
optic tract development suggest that the synthesis and transport of
particular membrane proteins may be directly related to the sequence of
morphological changes.