The regulation of tyrosine phosphorylation is critical in the growth and guidance of axons during the development of the vertebrate nervous system. Accumulating evidence suggests that receptor-type tyrosine phosphatases (RPTPs) play key roles in the signaling processes underlying axon growth. Several major classes of RPTP possess extracellular domains (ECDs) that are structurally similar to those of cell adhesion molecules (CAMs). Our overall hypothesis is that these CAM-like RPTPs, which are expressed on the surfaces of developing neurons, are involved both as regulatory ligands and as neuronal receptors in the regulation of vertebrate axon growth. Work in the previous granting period has established that 2 vertebrate RPTPs, PTP-delta and PTPRO, are strong candidates for axon growth regulation. In vitro, the ECD of PTP-delta is a neurite-promoting neuronal cell adhesion molecule that mediates attractive growth cone steering. PTP-delta can bind homophilically, and may be both a regulatory ligand and a neuronal receptor for these attractive cues. In contrast, the ECD of PTPRO is a neurite-inhibitory repulsive guidance cue in vitro. Knockdown of PTPRO or of PTP-delta expression in embryonic motor neurons leads to changes in axon growth. This proposal is designed to build on these observations.
In Aim 1, site-directed mutagenesis will be used to determine the regions of the PTP-delta and PTPRO ECDs responsible for functional binding.
In Aim 2, chimeric receptor production, neuronal transfection, and growth cone migration assays will be used to identify and characterize the receptor functions of PTP-delta.
In Aim 3, biochemical and functional approaches will be used to characterize PTPRO/Trk interactions and characterize novel PTPRO substrates. Finally, Aim 4 will use both the mouse and chick systems to characterize the in vivo roles of PTP-delta, PTPRO, and other CAM-like RPTPs in specific vertebrate axon guidance decisions. Our experiments will move the field closer to a molecular understanding of the role of tyrosine phosphorylation in vertebrate axon growth, by elucidating the roles of RPTPs. This is a critical background for efforts to understand how these processes go awry in developmental disorders of the brain and spinal cord.

Agency
National Institute of Health (NIH)
Institute
National Institute of Neurological Disorders and Stroke (NINDS)
Type
Research Project (R01)
Project #
5R01NS038920-08
Application #
7185067
Study Section
Neurodifferentiation, Plasticity, and Regeneration Study Section (NDPR)
Program Officer
Riddle, Robert D
Project Start
1999-07-15
Project End
2009-02-28
Budget Start
2007-03-01
Budget End
2008-02-29
Support Year
8
Fiscal Year
2007
Total Cost
$330,334
Indirect Cost
Name
University of Miami School of Medicine
Department
Pharmacology
Type
Schools of Medicine
DUNS #
052780918
City
Coral Gables
State
FL
Country
United States
Zip Code
33146
Tseng, Leinweih Andrew; Bixby, John L (2011) Interaction of an intracellular pentraxin with a BTB-Kelch protein is associated with ubiquitylation, aggregation and neuronal apoptosis. Mol Cell Neurosci 47:254-64
Kotani, Takenori; Murata, Yoji; Ohnishi, Hiroshi et al. (2010) Expression of PTPRO in the interneurons of adult mouse olfactory bulb. J Comp Neurol 518:119-36
Gonzalez-Brito, Manuel R; Bixby, John L (2009) Protein tyrosine phosphatase receptor type O regulates development and function of the sensory nervous system. Mol Cell Neurosci 42:458-65
Hower, Amy E; Beltran, Pedro J; Bixby, John L (2009) Dimerization of tyrosine phosphatase PTPRO decreases its activity and ability to inactivate TrkC. J Neurochem 110:1635-47
Gonzalez-Brito, Manuel R; Bixby, John L (2006) Differential activities in adhesion and neurite growth of fibronectin type III repeats in the PTP-delta extracellular domain. Int J Dev Neurosci 24:425-9
Chen, Bo; Bixby, John L (2005) Neuronal pentraxin with chromo domain (NPCD) is a novel class of protein expressed in multiple neuronal domains. J Comp Neurol 481:391-402
Chen, Bo; Bixby, John L (2005) A novel substrate of receptor tyrosine phosphatase PTPRO is required for nerve growth factor-induced process outgrowth. J Neurosci 25:880-8
Dimitropoulou, Anastasia; Bixby, John L (2005) Motor neurite outgrowth is selectively inhibited by cell surface MuSK and agrin. Mol Cell Neurosci 28:292-302
Stepanek, Laurie; Stoker, Andrew W; Stoeckli, Esther et al. (2005) Receptor tyrosine phosphatases guide vertebrate motor axons during development. J Neurosci 25:3813-23
Baerwald-de la Torre, Kristine; Winzen, Uwe; Halfter, Willi et al. (2004) Glycosaminoglycan-dependent and -independent inhibition of neurite outgrowth by agrin. J Neurochem 90:50-61

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