Analyses performed with mammalian cell cultures have indicated that the Src oncoprotein activates Jun NH2-terminal kinase JNK. However, strong in vivo data have been lacking. Tateno et al. now use Drosophila mutants to support this cell culture observation. A signaling pathway that includes the Drosophila JNK homolog Basket (Bsk) and the factor hemipterous (Hep) is required for the fusion of two epithelial sheets at the dorsal midline of the embryo. Like the known Bsk/Hep pathway components, a c-Src homolog DSrc42 is required to allow cell shape changes for successful embryonic closure. Hence, a physiological link is established between Src and JNK.