Acetylcholine receptors are required for postsynaptic aggregation driven by the agrin signalling pathway

Area of Science:

• Muscle cell biology
• Neuroscience
• Molecular biology

Background:

• Postsynaptic scaffolds assemble at neuromuscular junctions, requiring acetylcholine receptors (AChRs) and agrin signaling.
• Agrin signaling involves muscle-specific kinase (MuSK) and AChR beta subunit phosphorylation.
• The precise role of AChRs in postsynaptic molecule aggregation remains unclear.

Purpose of the Study:

• To investigate the role of acetylcholine receptors (AChRs) in postsynaptic molecule aggregation on muscle cells.
• To determine if AChRs are required for spontaneous or agrin-induced aggregation of postsynaptic molecules.

Main Methods:

• Utilized the 1R- genetic variant of C2 muscle cells with minimal AChR expression.
• Observed spontaneous and agrin-induced aggregation and colocalization of postsynaptic scaffold molecules.
• Assessed tyrosine phosphorylation of MuSK and the AChR beta subunit.

Main Results:

• Some postsynaptic scaffold molecules (including beta-dystroglycan and MuSK) spontaneously aggregated at low frequency in the absence of significant AChRs.
• Agrin did not increase the frequency of these spontaneous aggregations but induced MuSK tyrosine phosphorylation.
• AChRs were required for high-frequency aggregation driven by the agrin signaling pathway.

Conclusions:

• Postsynaptic scaffold molecules can form aggregates independently of AChRs.
• AChRs are essential for efficient, agrin-induced postsynaptic molecule aggregation.
• MuSK tyrosine phosphorylation likely precedes an AChR-dependent event necessary for robust postsynaptic assembly.