Movie 4.

Shh-mRuby3-positive particles released by the floorplate move retrogradely along axons and reach the soma of dI1 neurons. 150-min time-lapse sequence showing Shh-mRuby3-positive particles (magenta, white arrows) released from the floorplate, moving retrogradely along dI1 axons (magenta) and reaching the soma level of dI1 neurons in co-cultures of dorsal spinal cord- and floorplate explants. Maximum projections of z-stacks taken every 5 minutes. dI1 neurons were labelled by in ovo electroporation of Math1::EGFP-F and floorplate (FP) cells by Hoxa1::EGFP-F.