The long-term goal of our research is to understand molecular mechanisms underlying the formation of the neuromuscular junction, a cholinergic synapse between motoneurons and skeletal muscle fibers. This application focuses on signaling mechanisms in regulation of nicotinic acetylcholine receptor (AChR) synthesis. AChR is a pentameric ligand-gated ion channel that is concentrated at the neuromuscular junction. AChR expression is regulated both spatially and temporally during development. For example, AChR synthesis become confined at adult neuromuscular junction and when the synapse matures, the receptor subunit composition changes from gamma-subunit containing receptor to epsilon-subunit containing receptor. Neuregulin, a factor from motoneurons, increases whereas electrical activity of muscle cells inhibits AChR subunit expression. However, molecular signaling mechanisms in the regulation of AChR synthesis remain largely unknown. Our recent studies demonstrated that although neuregulin increases both epsilon- and gamma-mRNA, the signaling mechanisms involved are different: Neuregulin-mediated epsilon-mRNA increase requires de novo protein synthesis while that of gamma-subunit does not. We have also demonstrated that neuregulin-increased transcription of epsilon-subunit gene requires c-JUN and that neuregulin increases gamma-mRNA stability. Moreover, our results, both published and preliminary, suggest that two kinase signaling pathways are involved in regulating AChR synthesis: ERK activation leads to an increase in all five subunit mRNA whereas expression of gamma-mRNA appears to be inhibited by JNK. Based on these results, we hypothesize that synapse-specific synthesis and gamma-e subunit switch are mediated by integration of ERK and JNK signaling pathways.
The specific aims of the proposed research are designed to test this hypothesis. Specifically, we will 1) determine whether transcriptions of epsilon- and gamma-subunit genes are regulated by different mechanisms; 2) determine which signaling pathways regulate AChR mRNA stability; and 3) study signaling mechanisms of electrical activity to inhibit AChR expression and the cross-talk between neuregulin- and electrical activity-activated signaling pathways. The results of proposed experiments should contribute not only to our understanding of signaling mechanisms in regulation of AChR synthesis, but also to a more general understanding of synapse formation.

Agency
National Institute of Health (NIH)
Institute
National Institute of Neurological Disorders and Stroke (NINDS)
Type
Research Project (R01)
Project #
5R01NS040480-04
Application #
6627701
Study Section
Special Emphasis Panel (ZRG1-MDCN-7 (01))
Program Officer
Porter, Linda L
Project Start
2000-01-11
Project End
2004-09-14
Budget Start
2003-01-01
Budget End
2004-09-14
Support Year
4
Fiscal Year
2003
Total Cost
$319,391
Indirect Cost
Name
University of Alabama Birmingham
Department
Neurosciences
Type
Schools of Medicine
DUNS #
063690705
City
Birmingham
State
AL
Country
United States
Zip Code
35294
Xiong, Wen-Cheng; Mei, Lin (2017) Agrin to YAP in Cancer and Neuromuscular Junctions. Trends Cancer 3:247-248
Legay, Claire; Mei, Lin (2017) Moving forward with the neuromuscular junction. J Neurochem 142 Suppl 2:59-63
Li, Lei; Cao, Yu; Wu, Haitao et al. (2016) Enzymatic Activity of the Scaffold Protein Rapsyn for Synapse Formation. Neuron 92:1007-1019
Shen, Chengyong; Xiong, Wen C; Mei, Lin (2014) Caspase-3, shears for synapse pruning. Dev Cell 28:604-6
Liang, Chuan; Tao, Yanmei; Shen, Chengyong et al. (2012) Erbin is required for myelination in regenerated axons after injury. J Neurosci 32:15169-80
Wu, Haitao; Lu, Yisheng; Shen, Chengyong et al. (2012) Distinct roles of muscle and motoneuron LRP4 in neuromuscular junction formation. Neuron 75:94-107
Zhang, Bin; Xiong, Wen C; Mei, Lin (2009) Get ready to Wnt: prepatterning in neuromuscular junction formation. Dev Cell 16:325-7
Chen, Ping-Chung; Qin, Lu-Ning; Li, Xiao-Ming et al. (2009) The proteasome-associated deubiquitinating enzyme Usp14 is essential for the maintenance of synaptic ubiquitin levels and the development of neuromuscular junctions. J Neurosci 29:10909-19
Dobbins, G Clement; Luo, Shiwen; Yang, Zhihua et al. (2008) alpha-Actinin interacts with rapsyn in agrin-stimulated AChR clustering. Mol Brain 1:18
Zhang, Bin; Luo, Shiwen; Wang, Qiang et al. (2008) LRP4 serves as a coreceptor of agrin. Neuron 60:285-97

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