文摘
Netrins are secreted molecules that can attract or repel growth cones from a variety of organisms. In order to clarify the extent and scope of the effects of netrins for guiding growth cones, we have analyzednetrin-1awithin the relatively simple and well-characterized nervous system of zebrafish embryos.netrin-1ais expressed in dynamic patterns that suggest that it guides the growth cones of a wide variety of neurons. The spatiotemporal relationship ofnetrin-1aexpression and extending growth cones further suggests that netrins may act to delineate specific pathways and stimulate axonal outgrowth in addition to attracting and repelling growth cones. Furthermore, aberrant outgrowth by commissural growth cones in the spinal cords offloating headmutants, in whichnetrin-1aexpression is altered, is consistent with anin vivo,chemoattractive action ofnetrin-1a.These data suggest that netrins act on many growth cones and influence their behavior in a variety of ways.