The formation of the neuromuscular synapse requires a complex exchange of signals between the presynaptic nerve terminal and the postsynaptic muscle fiber. The genes essential for neuromuscular synapse formation remain incompletely characterized. One gene, Dok-7, is essential for neuromuscular synapse formation. However, how Dok-7 regulates synapse formation is poorly understood. This thesis is divided into four chapters. Chapters 1 and 2 are aimed at elucidating how Dok-7 mediates synapse formation. Chapter 3 and 4 explore the function of Abl tyrosine kinases in mammalian neuromuscular synapse formation and muscle patterning within the diaphragm muscle.
Agrin, released by motor neurons, promotes neuromuscular synapse formation by stimulating MuSK, a receptor tyrosine kinase expressed in skeletal muscle. Phosphorylated MuSK recruits docking protein-7 (Dok-7), an adaptor protein that is expressed selectively in muscle. In the absence of Dok-7, neuromuscular synapses fail to form, and mutations that impair Dok-7 are a major cause of congenital myasthenia in humans. How Dok-7 stimulates synaptic differentiation is poorly understood. Once recruited to MuSK, Dok-7 directly stimulates MuSK kinase activity. This unusual activity of an adapter protein is mediated by the N-terminal region of Dok-7, whereas most mutations that cause congenital myasthenia truncate the C-terminal domain. Here, we demonstrate that Dok-7 also functions downstream from MuSK, and we identify the proteins that are recruited to the C-terminal domain of Dok-7. We show that Agrin stimulates phosphorylation of two tyrosine residues in the C-terminal domain of Dok-7, which leads to recruitment of two adapter proteins: Crk and Crk-L. Furthermore, we show that selective inactivation of Crk and Crk-L in skeletal muscle leads to severe defects in neuromuscular synapses in vivo, revealing a critical role for Crk and Crk-L downstream from Dok-7 in presynaptic and post-synaptic differentiation.
|Advisor:||Burden, Steven J.|
|Commitee:||Chao, Moses V., Dasen, Jeremy S., Desplan, Claude, Sanes, Joshua R.|
|School:||New York University|
|Department:||Basic Medical Science|
|School Location:||United States -- New York|
|Source:||DAI-B 72/06, Dissertation Abstracts International|
|Subjects:||Neurosciences, Developmental biology|
|Keywords:||Acetylcholine receptors, Muscle-specific receptor tyrosine kinases, Neuromuscular junction, Neuromuscular synapses|
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