Deciphering how an axon grows, forms synaptic connections, and terminates axon outgrowth is essential if we are to understand how a nervous system is built. Such knowledge will be essential in harnessing the robust and resilient nature of the developing nervous system to design novel therapies for treating neurodevelopmental and neurodegenerative diseases. The long-term goal of our research program is to understand the cellular, developmental and molecular mechanisms that regulate synapse formation and axon termination. To this end, we rely upon C. elegans, a powerful model system that can be used to understand the fundamental principles governing construction of neural circuitry. The signaling protein RPM-1 is a key regulator of synapse formation and axon termination. Growing genetic evidence has linked RPM-1 signaling pathways to developmental disorders, such as schizophrenia and intellectual disability. The RPM-1 orthologs Highwire and Phr1 are also central regulators of axon degeneration. Thus, understanding how RPM-1 functions and how RPM-1 is regulated could significantly inform a range of conditions. In this proposal, we will further our understanding of how RPM-1 functions in axon termination and synapse formation on several levels. 1) We aim to understand on a cellular, developmental and molecular level why synapse formation defects occur in rpm-1 mutants. Our approach relies upon developmental time-course and real-time imaging to assess cellular deficits at the presynaptic terminals of rpm-1 mutants in order to test whether RPM-1 regulates synapse assembly or stability. We explore two mechanisms by which RPM-1 potentially affects synapse formation specifically, a putative MIG-15/NSY-1/JKK- 1/JNK-1 MAP kinase pathway and the tubulin acetyltransferase, ATAT-2. 2) We aim to determine whether RPM-1 functions in axon termination by regulating growth cone collapse. To do so, we rely upon in vivo cellular imaging, molecular genetics, and biochemistry. Our preliminary observations suggest that a Rac GTPase, MIG-2, is an important regulator of axon termination and growth cone collapse, which functions in the RPM-1 pathway. This is the first potential link between RPM-1 signaling and an actin regulator. 3) We aim to understand how RPM-1 is regulated. In preliminary studies using pharmacology and genetics to alter microtubule stability, we found evidence that RPM-1 regulates microtubule disassembly. This has revealed the intriguing possibility that a Tau-like protein, PTL-1, is a potential upstream, negative regulator of RPM-1, which we will test. In a complementary approach, we will explore the extracellular cues that regulate axon termination. In doing so, we aim to reveal further upstream regulators of RPM-1. Our observations suggesting that PTL-1 could regulate RPM-1 is particularly interesting given the strong links between the ortholog of PTL- 1, Tau, and neurodegenerative diseases, such as Alzheimer's disease.

Public Health Relevance

Neurodegenerative diseases and trauma to the CNS are major public health issues that afflict more than 50 million Americans yearly. This research program will lay the foundation for broad based and preventative therapies that will reduce the physical, emotional and financial impacts of these diseases on the public.

Agency
National Institute of Health (NIH)
Institute
National Institute of Neurological Disorders and Stroke (NINDS)
Type
Research Project (R01)
Project #
2R01NS072129-06A1
Application #
9237016
Study Section
Neurodifferentiation, Plasticity, and Regeneration Study Section (NDPR)
Program Officer
Talley, Edmund M
Project Start
2011-09-30
Project End
2020-06-30
Budget Start
2016-09-15
Budget End
2017-06-30
Support Year
6
Fiscal Year
2016
Total Cost
$531,005
Indirect Cost
$254,440
Name
Scripps Florida
Department
Type
DUNS #
148230662
City
Jupiter
State
FL
Country
United States
Zip Code
33458
Desbois, Muriel; Crawley, Oliver; Evans, Paul R et al. (2018) PAM forms an atypical SCF ubiquitin ligase complex that ubiquitinates and degrades NMNAT2. J Biol Chem 293:13897-13909
Opperman, Karla J; Mulcahy, Ben; Giles, Andrew C et al. (2017) The HECT Family Ubiquitin Ligase EEL-1 Regulates Neuronal Function and Development. Cell Rep 19:822-835
Baker, Scott T; Grill, Brock (2017) Defining Minimal Binding Regions in Regulator of Presynaptic Morphology 1 (RPM-1) Using Caenorhabditis elegans Neurons Reveals Differential Signaling Complexes. J Biol Chem 292:2519-2530
Borgen, Melissa A; Wang, Dandan; Grill, Brock (2017) RPM-1 regulates axon termination by affecting growth cone collapse and microtubule stability. Development 144:4658-4672
Crawley, Oliver; Giles, Andrew C; Desbois, Muriel et al. (2017) A MIG-15/JNK-1 MAP kinase cascade opposes RPM-1 signaling in synapse formation and learning. PLoS Genet 13:e1007095
Risley, Monica G; Kelly, Stephanie P; Jia, Kailiang et al. (2016) Modulating Behavior in C. elegans Using Electroshock and Antiepileptic Drugs. PLoS One 11:e0163786
Baker, Scott T; Turgeon, Shane M; Tulgren, Erik D et al. (2015) Neuronal development in Caenorhabditis elegans is regulated by inhibition of an MLK MAP kinase pathway. Genetics 199:151-6
Giles, Andrew C; Opperman, Karla J; Rankin, Catharine H et al. (2015) Developmental Function of the PHR Protein RPM-1 Is Required for Learning in Caenorhabditis elegans. G3 (Bethesda) 5:2745-57
Sharma, Jaiprakash; Baker, Scott T; Turgeon, Shane M et al. (2014) Identification of a peptide inhibitor of the RPM-1 ยท FSN-1 ubiquitin ligase complex. J Biol Chem 289:34654-66
Baker, Scott T; Opperman, Karla J; Tulgren, Erik D et al. (2014) RPM-1 uses both ubiquitin ligase and phosphatase-based mechanisms to regulate DLK-1 during neuronal development. PLoS Genet 10:e1004297

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