bicoid RNA localization requires the trans-Golgi network

Abstract Background The formation of thebicoid(bcd) mRNA gradient is a crucial step for Bcd protein gradient formation inDrosophila. In the past, a microtubule (MT)-based cortical network had been shown to be indispensable forbcdmRNA transport to the posterior. Results We report the identification of a MT-binding protein CLASP/Chb as the first component associated with this cortical MT network. Since CLASPs in vertebrates were shown to serve as an acentriolar microtubule organization center (aMTOC) in concert withtrans-Golgi proteins, we examined the effect of theDrosophila trans-Golgins onbcdlocalization and gradient formation. Using a genetic approach, we demonstrate that theDrosophila trans-GolginsdGCC88,dGolgin97anddGCC185indeed affectbcdmRNA localization during oocyte development. Consequently, thebcdmRNA is already mislocalized before the egg is fertilized. The expression domains of genes downstream of the hierarchy ofbcd, e.g. of the gap geneempty spiraclesor of the pair-rule geneeven-skippedare changed, indicating an altered segmental anlagen, due to a faultybcdgradient. Thus, at the end of embryogenesis,trans-Golgin mutants showbcd-like cuticle phenotypes. Conclusions Our data provides evidence that the Golgi as a cellular member of the secretory pathway exerts control onbcdlocalization which indicates thatbcdgradient formation is probably more intricate than previously presumed.