During Drosophila embryogenesis, the ventral epidermis dorsally expands and the left and right epithelial sheets meet and fuse along the dorsal midline. For this dorsal closure to occur, two PDZ domain proteins, Cno and ZO-1, are required. The dorsal epidermis remains open when the expression of ZO-1 and Cno are reduced simultaneously by hypomorphic mutations in the relevant loci. ZO-1 and Cno colocalize at adherens junctions in embryonic epithelia, and form a protein complex upon binding to each other. Genetic analysis showed that Cno is involved in the Jun N-terminal kinase (JNK) pathway for dorsal closure, as a modulator acting upstream of, or in parallel with, the small GTPase Drac1. The ZO-1-Cno complex may be involved in dynamic changes in cytoskeletal organization and cell adhesion during morphogenetic events associated with dorsal closure in the Drosophila embryo.
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