The turnout gene acts cell non-autonomously.

(A, B, C) Donor cells are labeled with rhodamine dextran (red), and host embryos were stained with SV2 antibody (green) to reveal all motor axonal trajectories. (A) Wild-type donor-derived neurons (red) in a wild-type host display no guidance or branching defects (0/20). (B) Wild-type donor-derived neurons in a mutant host display precocious branching upon exiting the spinal cord (arrow, 9/18). (C) Mutant donor-derived motor axons display no defects in a wild-type host environment (0/6). Scale bar, 15 µm.