Fig. 6: Oskar linker region controls Smaug localization and nanos translation.
From: Direct observation of translational activation by a ribonucleoprotein granule
a, AlphaFold structure model of short Oskar protein, with LOTUS domain in red, SGNH-like domain in blue and linker region in green. b, Percentage of glutamine (Q) and asparagine (N) in three regions of short Oskar proteins from 11 Drosophila species. Each dot represents the Oskar protein of a particular Drosophila species. c, Embryos expressing Oskar-WT/NQmut-bcd 3′ UTR are immunostained with anti-Oskar antibody. d, Distribution of Smaug in germplasm. Images of germplasm induced by ectopic Oskar-WT or Oskar-NQmut at the anterior pole. Germ granules are labelled by Vasa–mApple (magenta). Smaug is visualized with Smaug–GFP (green). e, Intensity profiles of Vasa–mApple (magenta) and Smaug–GFP (green) along the lines across the germ granules induced by Oskar-WT or Oskar-NQmut. The data are the mean ± s.d. of 20 germ granules from 3 embryos for each genotype. f, Representative images showing the translation of suntag-nanos mRNA in germplasm induced by Oskar-WT or Oskar-NQmut. Blue, Vasa; magenta, suntag smFISH; green, anti-GCN4. g, Fraction of suntag-nanos-WT or suntag-nanos-SREmut mRNA translated in anterior germplasm induced by Oskar-WT or Oskar-NQmut. Each dot represents the normalized measurement of an embryo where the translating fraction in the anterior germplasm is divided by the translating fraction in the native germplasm at the posterior. Statistical comparisons between Oskar-WT and NQmut were performed by two-tailed t-test. nnanosWT-OskarWT = 7, nnanosWT-OskarNQ = 6, nnanosSRE-OskarWT = 7, nnanosSRE-OskarNQ = 5. The data are the mean ± s.d. h, Cuticle phenotypes generated by Oskar-WT/NQmut-bcd 3′ UTR. The images show a range of cuticle phenotypes corresponding to different levels of anteriorly expressed Nanos protein. The bar graph shows the frequency of each cuticle phenotype caused by Oskar-WT/NQmut-bcd 3′ UTR expression. Statistical comparison was performed using chi-square test. i, Oskar mediates Smaug localization and translational derepression of nanos mRNA. With wild-type Oskar, Smaug, but not its co-factors for translational repression (Cup/CCR4-NOT), localized to germ granules. Localized Smaug is dysfunctional in translational repression, allowing the translation of nanos mRNA. In Oskar-NQmut germplasm, Smaug loses localization in germ granules but gains functionality inside germ granules, thus repressing the translation of nanos mRNA.
