Molecules microinjected in the yolk sac are rapidly delivered into the embryo. (A) Schematic representation of the site of injection in one-cell zebrafish embryo. (B) Visualization of FITC labelled EcLPS upon microinjection into the yolk sac. Embryos were microinjected with 3.5 ng LPS from E. coli strains 0111:B4 conjugated with FITC and examined at the indicated times with a LUMAR stereomicroscope. hpi, hours post-injection.