Conserved signals and machinery for RNA transport in Drosophila oogenesis and embryogenesis.

Localization of cytoplasmic messenger RNA transcripts is widely used to target proteins within cells. For many transcripts, localization depends on cis-acting elements within the transcripts and on microtubule-based motors; however, little is known about other components of the transport machinery or how these components recognize specific RNA cargoes. Here, we show that in Drosophila the same machinery and RNA signals drive specific accumulation of maternal RNAs in the early oocyte and apical transcript localization in blastoderm embryos. We demonstrate in vivo that Egalitarian (Egl) and Bicaudal D (BicD), maternal proteins required for oocyte determination, are selectively recruited by, and co-transported with, localizing transcripts in blastoderm embryos, and that interfering with the activities of Egl and BicD blocks apical localization. We propose that Egl and BicD are core components of a selective dynein motor complex that drives transcript localization in a variety of tissues.