Figure 7.

slpr, encoding Drosophila MLK, is the MKKK for the Jun kinase pathway during dorsal closure in the fly. A canonical signaling pathway is indicated at left. Examples of mammalian proteins participating at each step are indicated at right. In Drosophila, dorsal closure involves signaling through the JNK pathway to control gene expression and cell sheet morphogenesis. Although the initiating signal is not known, it is likely that an early event is activation of dRac1, which by analogy to signal transduction with mammalian MKKKKs, participates with Msn to activate Slpr, the JNKKK. Sequential phosphorylation events through the kinase module, Slpr, Hep, and Bsk, lead to activation of dJun, regulation of gene expression, and cell sheet movement.