Je. Minturn et al., TOAD-64, A GENE EXPRESSED EARLY IN NEURONAL DIFFERENTIATION IN THE RAT, IS RELATED TO UNC-33, A C-ELEGANS GENE INVOLVED IN AXON OUTGROWTH, The Journal of neuroscience, 15(10), 1995, pp. 6757-6766
Using two-dimensional gel electrophoresis we previously identified mem
brane-associated proteins that are upregulated over the course of neur
ogenesis. One of these, TOAD-64 (Turned On After Division, 64 kDa), is
expressed immediately after neuronal birth and is dramatically downre
gulated in the adult. The gene encoding TOAD-64 has now been cloned, a
nd its sequence shows homology to the unc-33 gene from C. elegans, mut
ations in which lead to aberrations in axon outgrowth. Northern and in
situ hybridization show that TOAD-64 mRNA is enriched in the nervous
system and is developmentally regulated in parallel with the protein.
The expression of the TOAD-64 protein and gene coincident with initial
neuronal differentiation and the downregulation when the majority of
axon growth is complete suggests a role in axon elaboration. Three add
itional lines of evidence support this possibility: TOAD-64 is upregul
ated following neuronal induction of pig and PC12 cells; the protein i
s found in lamellipodia and filopodia of growth cones; and axotomy of
the sciatic nerve induces reexpression. While the sequence of TOAD-64
lacks a signal sequence and therefore is likely to encode a cytoplasmi
c protein, biochemical experiments demonstrate that the protein is tig
htly, but noncovalently, associated with membranes. The data presented
here suggest that TOAD-64 could be a central element in the machinery
underlying axonal outgrowth and pathfinding, perhaps playing a role i
n the signal transduction processes that permit growing axons to choos
e correct routes and targets.