Morphogenesis shapes pattern and size during development. The initiation and propagation of morphogenetic processes is led by the integrated activation of signaling cascades. Much is known about regulatory control of signaling cascades in cell culture systems. However, how this regulatory elements act when cells need to behave coordinately is still unknown territory. The morphogenetic process of dorsal closure proceeds through changes in cell shape and polarity under the control of JNK signaling. Amongst other regulatory elements, Puckered, a Drosophila MAPK phosphatase, is involved in a negative feedback loop that controls JNK signaling activity. puckered is expressed in many other tissues, could influence other developmental events and might regulate different signaling cascades. The negative regulatory control of signal transduction pathways could be a general mechanism regulating differentiation and morphogenesis.