Anterior-posterior (AP) axis patterning in Drosophila embryos requires the posterior localization of the translational regulator Nanos,which is brought about by the prior posterior localization of nanosmRNA. This localization process is mediated by a signal in the 3′untranslated region of nanos, which, because of its complexity, has hindered the identification of the trans-acting factors that drive nanos mRNA localization. Now, Roshan Jain and Elizabeth Gavis have discovered that Rumpelstiltskin (Rump), a Drosophila heterogeneous nuclear ribonucleoprotein (hnRNP) M homolog, regulates nanos mRNA localization (see ). The researchers identified Rump as a protein that binds to the nanos +2′ localization element by RNA-affinity purification. They show that Rump recognizes two CGUU motifs in this element in vitro that are needed for posterior localization by this element in vivo. Finally,analysis of a rump-null mutant shows that Rump regulates AP patterning by playing a direct role in localizing nanos RNA, thus providing the first example of an hnRNP M homolog regulating mRNA localization.
