Movie 6.

Artery-directed reverse migration of ECs is defective in cxcr4a^um20 mutants. Maximum intensity projections of confocal z-stacks of Tg(fli1a:nEGFP)^y7; Tg(-0.8flt1:RFP)hu⁵³³³ double transgenic cxcr4a^um20 mutants, labelling all EC nuclei (green) and all arterial ECs (red). White arrowheads with numbers mark individual ECs. Note accumulation of arterialised ECs at the tip of the sprout and absence of reverse migration.