Wnt proteins regulate acetylcholine receptor clustering in muscle cells.
BACKGROUND
The neuromuscular junction (NMJ) is a cholinergic synapse that rapidly conveys signals from motoneurons to muscle cells and exhibits a high degree of subcellular specialization characteristic of chemical synapses. NMJ formation requires agrin and its coreceptors LRP4 and MuSK. Increasing evidence indicates that Wnt signaling regulates NMJ formation in Drosophila, C. elegans and zebrafish.


RESULTS
In the study we systematically studied the effect of all 19 different Wnts in mammals on acetylcholine receptor (AChR) cluster formation. We identified five Wnts (Wnt9a, Wnt9b, Wnt10b, Wnt11, and Wnt16) that are able to stimulate AChR clustering, of which Wnt9a and Wnt11 are expressed abundantly in developing muscles. Using Wnt9a and Wnt11 as example, we demonstrated that Wnt induction of AChR clusters was dose-dependent and non-additive to that of agrin, suggesting that Wnts may act via similar pathways to induce AChR clusters. We provide evidence that Wnt9a and Wnt11 bind directly to the extracellular domain of MuSK, to induce MuSK dimerization and subsequent tyrosine phosphorylation of the kinase. In addition, Wnt-induced AChR clustering requires LRP4.


CONCLUSIONS
These results identify Wnts as new players in AChR cluster formation, which act in a manner that requires both MuSK and LRP4, revealing a novel function of LRP4.
Department of Neurology and Institute of Molecular Medicine and Genetics, Georgia Health Sciences University, Augusta, Georgia 30912, USA.
Bin
B
Zhang
Chuan
C
Liang
Ryan
R
Bates
Yiming
Y
Yin
Wen-Cheng
WC
Xiong
Lin
L
Mei
D018171:Agrin / Q000494:pharmacology; D000818:Animals; D016000:Cluster Analysis; D057809:HEK293 Cells; D006801:Humans; D026502:LDL-Receptor Related Proteins; D051379:Mice; D032342:Muscle Cells / Q000187:drug effects / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D011485:Protein Binding / Q000187:drug effects; D055503:Protein Multimerization / Q000187:drug effects; D020794:Receptor Protein-Tyrosine Kinases / Q000378:metabolism; D011950:Receptors, Cholinergic / Q000378:metabolism*; D011973:Receptors, LDL / Q000378:metabolism; D051153:Wnt Proteins / Q000378:metabolism*
D018171:Agrin; D026502:LDL-Receptor Related Proteins; C116415:Lrp4 protein, mouse; D011950:Receptors, Cholinergic; D011973:Receptors, LDL; D051153:Wnt Proteins; C511695:MuSK protein, mouse; D020794:Receptor Protein-Tyrosine Kinases