Fig. 5. FGF is required for rosette assembly, a prerequisite for primordium migration. Primordia of cxcr4b mutant embryos treated with DMSO (A) or SU5402 (B), showing the complete disappearance of rosettes after blocking the FGF pathway for 6 hours. (C,D) Time-lapse analysis and corresponding kymograph showing the progressive melting of rosettes after treatment with 80 µM SU5402. The migration speed is normal (70 µm/hour) and remains constant during this phase. Scale bar: 50 µm. (E,F) Time-lapse analysis and corresponding kymograph of a washout experiment showing that five rosettes (red arrows in E,F) simultaneously reassemble before migration resumes. Three phases can be distinguished on the kymograph: (1) uncoordinated migration, (2) rosette reassembly, and (3) migration recovery. (G,H) Expression of Fgf ligands in cldnb:gfp embryos treated for 6 hours with SU5402. Lower panels are transmission images of NBT/BCIP stainings. fgf3 (G) and fgf10 (H) are strongly expressed throughout the primordium when Fgfr is blocked. Scale bars: 20 µm (unless stated otherwise).