RNA Localization Requires the -Golgi Network

Background: The formation of the () mRNA gradient is a crucial step for Bcd protein gradient formation in . In the past, a microtubule (MT)-based cortical network had been shown to be indispensable for mRNA 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 with -Golgi proteins, we examined the effect of the -Golgins on localization and gradient formation. Using a genetic approach, we demonstrate that the -Golgins , and indeed affect mRNA localization during oocyte development. Consequently, the mRNA is already mislocalized before the egg is fertilized. The expression domains of genes downstream of the hierarchy of , e.g. of the gap gene or of the pair-rule gene are changed, indicating an altered segmental anlagen, due to a faulty gradient. Thus, at the end of embryogenesis, -Golgin mutants show -like cuticle phenotypes.

Conclusions: Our data provides evidence that the Golgi as a cellular member of the secretory pathway exerts control on localization which indicates that gradient formation is probably more intricate than previously presumed.