Mutual interference of Staufen and Egl during oskar mRNA localization. (A–F) Representative micrographs of the distribution of endogenous oskar mRNA (detected by smFISH; blue—low intensity RNA signal, yellow—high intensity RNA signal, see scale in F) in stage 9 oocytes (anterior to the left, posterior to the right) showing ectopic anterior accumulation of oskar mRNA in oocytes lacking Staufen protein (B; see also Fig. 1 A′), overexpressing Egl (C) or heterozygous for one copy of the dominant, hyperactive BicD¹ allele (E). Anterior accumulation of oskar is not observed in wild-type oocytes (A), or upon Staufen overexpression in Egl-overexpressing oocytes (D) or BicD¹/+ oocytes (F). Scale bar represents 20 μm.