title: 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.
abstract: Using two-dimensional gel electrophoresis we previously identified membrane-associated proteins that are upregulated over the course of neurogenesis. One of these, TOAD-64 (Turned On After Division, 64 kDa), is expressed immediately after neuronal birth and is dramatically downregulated in the adult. The gene encoding TOAD-64 has now been cloned, and its sequence shows homology to the unc-33 gene from C. elegans, mutations 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 additional lines of evidence support this possibility: TOAD-64 is upregulated following neuronal induction of P19 and PC12 cells; the protein is 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 cytoplasmic protein, biochemical experiments demonstrate that the protein is tightly, 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 in the signal transduction processes that permit growing axons to choose correct routes and targets.
mesh_terms: D000375:Aging / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D001369:Axons / Q000502:physiology*; D001483:Base Sequence; D017173:Caenorhabditis elegans / Q000235:genetics*; D002454:Cell Differentiation; D002460:Cell Line; D003001:Cloning, Molecular; D003714:Denervation; D015870:Gene Expression; D008565:Membrane Proteins / Q000378:metabolism; D008969:Molecular Sequence Data; D009420:Nervous System / Q000254:growth & development / Q000378:metabolism; D009474:Neurons / Q000166:cytology*; D016716:PC12 Cells; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats
chemical_list: D008565:Membrane Proteins; D012333:RNA, Messenger