Table 1

Partial listing of molecules contributing to RGC axon guidance

Guidance family	Mode of action	Reported effect on RGC axons	Location in developing visual system	Remarks	Known receptors	Selected references
Netrins	Secreted	Attractive	Optic disc, optic nerve	Homology to laminin	DCC, UNC5	12

Semaphorins	Secreted and membrane bound	Inhibitory?	Retina?	Large family (>20 members) semaphorin domain	Neuropilins plexins	28, 29

Slits	Secreted	Inhibitory	Retina, optic nerve, optic chiasm, optic tract	Form boundaries for RGC axons	Robos	20, 21, 22

Ephrins	Secreted and membrane bound	Inhibitory	Retina, superior colliculus	Two subclasses: ephrin-A and ephrin-B form gradients in retina and tectum	EphA receptors EphB receptors	34, 35

EphB proteins	Membrane bound	Inhibitory	Retina	“Reverse” signalling through ephrins	Ephrin B proteins	39, 40

L1	Membrane bound	Attractive	Expressed on RGC axons	Ig superfamily member maintains RGC axon fasiculation	Homophilic binding	7, 8, 60

Laminin	Extracellular matrix	Growth promoting	Retina	Commonly used as substrate for RGC axon growth in vitro	Integrins	61, 62
Tenascin	Extracellular matrix	Inhibitory	Optic nerve	Expression begins after embryogenesis	Unknown	55
Chondroitin sulphate	Extracellular matrix	Inhibitory	Retina	Inhibitory ring in outer retina	Unknown	13, 14