Tadpoles are a model system for neural development and have well-characterized retinal ganglion cells that guide axons out of the retina. This is promoted by gradients of the guidance cue netrin. There is a poorly named protein called “deleted in colectoral cancer” (DCC) that acts as the netrin-1 receptor.
Manitt et al used DCC primary antibodies, IgG secondary antibodies coupled to 1 nm gold particles, and then serial section TEM to visualize this system. The picture below shows that DCC is present on presynaptic vescicles (arrows in J + K), the surface of presynaptic membranes (L), and on the surface of axonal filopedia (M). It also indicates synapses via triangles, and has scale bars of 200 nm:
This is consistent with their model that DCC receptor proteins mediate netrin signaling in axon pathfinding and synaptogenesis. BDNF is another molecule that promotes both increased synaptic density and axon branching. But they have slightly different mechanisms, showing that different cues can lead to the subtly differences in neural circuitry that defines the developing brain.
Manitt et al, 2009. doi:10.1523/JNEUROSCI.0947-09.2009. Pubmed here.