Figure 8.

A model for GON-1 function in maintaining synapse morphology at the NMJ. A, In wild-type worms, GON-1 may function to degrade collagen IV/EMB-9, which is stabilized by fibulin/FBL-1, or transform it from a pro-growth to a pro-stability conformation. B, In the absence of GON-1, overabundance of pro-growth EMB-9 may lead to an overgrowth of the muscle, including the muscle arms. Since trans-synaptic adhesion molecules reside at synapses (white and black bars), muscle arm overgrowth may pull on presynaptic varicosities causing the presynaptic protrusions exhibited by these mutants. These protrusions are filled with clear-core and dense-core vesicles containing synaptic vesicle and active zone proteins (white and black circles).