Traction on immobilized netrin-1 is sufficient to reorient axons

Abstract

During embryonic development, axons are guided to their target by patterning proteins encountered along their trajectory. These cues can be linked to the cells that produce them or secreted into the extracellular matrix. Whether secreted cues, like netrin-1, provide traction for the growth cone when they become attached to the extracellular matrix is unclear. Advancing spinal commissural neuron growth cones were shown to generate local forces of 4 to 15 piconewtons but, when confronted with immobilized netrin-1, generated traction forces in excess of 63 piconewtons on netrin-1 that can redirect the trajectory of the axon.

Fig. 1

(A) A netrin-1 bead is presented and released upon contact on one side of the growth cone. After 22 min., another bead is presented, but this time it is attached to the substrate (marked ‘X’). Scale bar = 10μm. (B) Traces of axons confronted with unrestrained or immobilized netrin-1 beads. Vertical axis is the initial trajectory of the axon, while the dotted line marks a 20° angle. None of the 13 axons assayed turned at an angle >20° when unrestrained, while 10 of the 15 axons reoriented to immobilized beads. (C) Percent of beads pulled with >63 pN within 8 min (Ab = unspecific antibodies). The number of growth cones assayed is indicated above or within each bar. Error bars are S.E.M and ** = p<0.01 relative to netrin-1 (Tukey).