PF06260933 (Sigma-Aldrich) was added immediately following embryo collection to a final concentration of 1, 5, or 10 μM. Water was changed on the second day, with fresh drug applied. For inhibition of MEK, PD0325901 (Sigma-Aldrich) in dimethyl sulfoxide (DMSO) was added to a final concentration of 1 μM, while the FGFR inhibitor SU5402 (Sigma-Aldrich) in DMSO was used at a concentration of 5 μM. These concentrations were previously shown to rescue embryo elongation caused by MEK (43 (link), 44 (link)). Control embryos were treated with an equivalent amount of DMSO. Both drugs were applied from 4.5 hpf until imaging (35 (link)).