A direct interaction of axonin-1 with NgCAM-related cell adhesion molecule(NrCAM) results in guidance, but not growth of commissural axone

An interaction of growth cone axonin-1 with the floor-plate NgCAM-related c ell adhesion molecule (NrCAM) was shown to play a crucial role in commissur al axon guidance across the midline of the spinal cord. We now provide evid ence that axonin-1 mediates a guidance signal without promoting axon elonga tion. In an in vitro assay, commissural axons grew preferentially on stripe s coated with a mixture of NrCAM and NgCAM. This preference was abolished i n the presence of anti-axonin-1 antibodies without a decrease in neurite le ngth. Consistent with these findings, commissural axons in vivo only fail t o extend along the longitudinal axis when both NrCAM and NgCAM interactions , but not when axonin-1 and NrCAM or axonin-1 and NgCAM interactions, are p erturbed. Thus, we conclude that axonin-1 is involved in guidance of commis sural axons without promoting their growth.