Abstract
The Toll-Dorsal pathway was identified to participate in dorsoventral axis formation of Drosophila embryo. Previous screenings had identified 15 dorsal group genes that were arranged in a linear pathway. Toll is activated by the binding of its ligand Spätzle. Upon Toll activation, it interacts with the adaptor proteins DmMyD88, Tube and the kinase Pelle, and triggers degradation of the inhibitor Cactus, thus allowing the nuclear translocation of the transcription factor Dorsal/Dif. weckle (wek) was previously identified as a new dorsal group gene that encodes a putative zinc-finger transcription factor. However, its role in Toll pathway was unknown. Here, we isolated new wek alleles and demonstrated that wek acts upstream of cactus but downstream of Toll. Although wek encodes a zinc-finger protein, it localizes to the plasma membrane of embryos, independent of Toll signaling. Wek forms homodimer and associates with Toll. Moreover, Wek binds to DmMyD88 and localizes it to the plasma membrane. Thus, Wek acts as an adaptor to assemble/stabilize a Toll/Wek/DmMyD88/Tube complex. The Toll pathway was also identified to involve in the innate immune response of adult fly. However, different from the membrane localization of embryos, Wek localized to the nucleus of fat body cells. Unlike the DmMyD88/tube/pelle/cactus gene cassette of the Toll pathway in embryo, wek plays a minimal role in the immune defense against Gram-positive bacteria and fungi.