Kephalaea is a novel modulator of decapentaplegic signaling and defines requirements for signaling during head involution in Drosophila

Dorsal closure is the morphogenetic process by which the Drosophila melanogaster embryo becomes completely encased in cuticle-secreting epidermis. Epithelial cells on either side of the embryo spread dorsally and replace the amnioserosa, meeting and fusing along the dorsal midline to create a continuous epidermal sheet. Failure of this process results in embryonic lethality characterized by defects in the dorsal epidermis most often manifest as a single large hole in the dorsal cuticle. Dorsal-open group genes define two groups of molecules: those that contribute to closure as components of signaling cascades and those that act as mechanical effectors of closure. Cell shape changes are mediated by the mechanical effectors (cytoskeletal, junction and adhesion molecules) and are controlled by the Jun N-terminal Kinase (JNK) and Decapentaplegic (Dpp) signaling pathways. The JNK cascade is required for activation of the Dpp pathway, but both signals contribute to morphogenesis independently. The links between signaling events and cell shape change have not been identified. Here I describe the identification and characterization of a novel dorsal closure locus, kephalaea keph. Genetic evidence places keph in the Dpp signaling pathway. However, keph also interacts with JNK signaling components and mechanical effectors, suggesting that Keph may function in the integration of the JNK and Dpp signals or in the transmission of signaling to the mechanical effectors. The keph locus encodes a novel protein with no characterized domains or motifs that would suggest a biochemical function for the protein. I propose that Keph functions downstream of Dpp and JNK to link signaling events to morphogenesis driven by the mechanical effectors. In addition to its role in dorsal closure, Keph also functions in head involution, and identifies a requirement for Dpp signaling in this morphogenetic process.